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How to avoid specific complications of total ankle replacement
Foot Ankle Clin N Am 7 (2002) 765 – 789
How to avoid specific complications of total ankle replacement Emmanouil D. Stamatis, MDa, Mark S. Myerson, MDb,* a
Department of Orthopaedic Surgery, The Union Memorial Hospital, Union Memorial Orthopaedics, The Johnston Professional Building, #400, 3333 North Calvert Street, Baltimore, MD 21218, USA b Institute for Foot and Ankle Reconstruction, Mercy Hospital, 301 St. Paul Place, Baltimore, MD 21202, USA
Degenerative arthritis of the ankle joint, whether idiopathic, traumatic, or from a systemic process, presents a significant orthopedic problem. Orthopedic surgeons have traditionally performed ankle arthrodesis, but this procedure is associated with considerable morbidity, potential complications, and long-term adverse effects. It has been assumed that improved arthrodesis techniques would bring improved outcomes, but this has not been the case at all. After arthrodesis, prolonged immobilization leads to a marked loss of subtalar motion, partly from the arthrodesis itself and partly from prolonged immobilization [1]. Although some investigators have reported a high rate of union [2,3], nonunion has been reported in the recent literature as high as 41% [4]. There are also other issues that are not always taken into consideration, including persistent pain and an abnormal gait in a high percentage of patients even after a successful arthrodesis [5]. Perhaps the most important aspect of ankle arthrodesis is not whether fusion occurs, but what the effect of the arthrodesis is on the remaining function of the foot. The increased stress on adjacent joints, with subsequent increased rates of degenerative arthritis, is worrisome [1,6]. Although issues like nonunion are a complication of the procedure itself, other issues occur because adjacent joints are affected by ankle motion limitations. This concern raises questions related to the routine use of ankle arthrodesis in younger patients. Alternative surgical procedures have emerged over the past decade as viable options for the treatment of ankle joint arthritis, including supramalleolar osteotomy, distraction ankle arthroplasty, allograft joint replacement, and total ankle replacement. Supramalleolar osteotomy has played a role in the management of ankle arthritis, particularly in the presence of distal tibial malalignment that was either * Corresponding author. E-mail address: [email protected] (M.S. Myerson). 1083-7515/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S 1 0 8 3 - 7 5 1 5 ( 0 2 ) 0 0 0 5 7 - 8
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idiopathic [7] or secondary to trauma [8,9]. There are also a few reports on the role of the supramalleolar osteotomy for the treatment of other types of arthritis [10,11], but in these limited series the investigators tried to create a plantigrade foot rather than to treat the ankle joint arthritis itself. We have been encouraged by the use of supramalleolar osteotomy at our institution, but we have found that this procedure has a predominant role in the presence of mechanical malalignment. Distraction ankle arthroplasty has been reported by Van Valburg et al [12] as an alternative method of treatment for ankle arthritis. In an earlier report of our experience with this technique [13], our results were disappointing in that most of these patients reported little functional improvement. Since that time we have initiated an alternative method of distraction including the use of fascial interposition arthroplasty; however, the results of this newer technique have yet to be examined. The first total ankle replacement was performed in 1970 by Lord and Marrott [14], but the results were unsatisfactory and the implant was abandoned. Other total ankle implants were released in the early 1970s, but these were all associated with significant complications and long-term unpredictability, and the procedure was abandoned by most surgeons [15 – 19]. Inappropriate patient selection, implant design problems, poor cement technique, lack of adequate and accurate instrumentation, and lack of adequate revision options caused by significant amounts of bone resection during the initial procedure were some of the most significant problems with the first-generation implants. Despite these disappointing results, the deleterious long-term side effects of ankle arthrodesis along with the potential complications refueled the continued search for a reliable implant. The second generation of ankle implants has relied on metallurgy improvements, more sophisticated instrumentation, and a better understanding of ankle joint biomechanics. There has also been a trend for prostheses that use biologic fixation, which has also been shown to give better results than cemented implants [20,21]. Despite these improvements, for many surgeons total ankle replacement remains a complex procedure with an unpredictable outcome. For most surgeons familiar with ankle replacement, this procedure is indicated for patients with low demands and minimal tibiotalar deformity. As noted by Conti and Wong [22], the published results of second-generation ankle replacement systems are limited [20,23 – 26] and the data presented are retrospective and often anecdotal. The science behind the ankle implants has evolved tremendously during the last 15 years, as has the experience and the recognition of the crucial factors predisposing to an unsuccessful outcome. It is now accepted that total ankle replacement is a technically difficult procedure that demands foot and ankle expertise. The learning curve is long and steep, and meticulous attention to detail is required. Complications and intraoperative difficulties with total ankle replacement have been well described, and the possible pitfalls and their solutions have been discussed. After the accumulated experience of the senior author with more than 200 total ankle replacement procedures using the Agility prosthesis (DePuy,
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Warsaw, IN), we have found that many of the technical problems and errors experienced earlier are no longer as much of an issue. The potential successful outcome of this procedure mainly depends on the elimination of complications such as inadequate postoperative range of motion, inadequate fixation of the implant with late subsidence, and inadequate correction of preoperative foot and ankle deformities that create an unfavorable mechanical environment for the prosthesis. Thus, this article focuses on the factors affecting postoperative range of motion, our technique to enhance the union rate of the distal tibiofibular or syndesmosis arthrodesis, and our approach to correction of the varus-valgus deformities of the ankle joint and any other concomitant deformities of the hindfoot and midfoot.
Ankle gait and clinical implications of the stiff total ankle replacement The total range of motion of the ankle joint in the sagittal plane is approximately 45, but there is great variation among patients, because dorsiflexion ranges between 10 and 23 and plantarflexion between 25 and 35 [27]. Several researchers have studied the range of motion of the ankle joint in normal gait and found dorsiflexion averaged 10 and plantarflexion averaged 20 [28]. Stauffer et al [29] reported that the range of motion averaged 24 during normal gait, 10 of this motion dorsiflexion and 14 plantarflexion. Approximately 37 of motion is used for ascending stairs and 56 for descending stairs. Approximately 14 of motion is used in the stance phase of gait, with reduced dorsiflexion mainly affecting the midstance phase and reduced plantarflexion affecting the heel strike and toe-off phases. Interestingly, similar amounts of dorsiflexion and even less plantarflexion are adequate for walking at a pace 50% faster than normal walking speed [29]. Inadequate dorsiflexion during the midstance phase leads to a recurvatum thrust on the knee joint, inadequate propelling of the leg over the foot, an uneven gait, and increased stress concentration across the midfoot. Inadequate plantarflexion leads to increased pressure on the heel during heel strike and weak toe-off. These same parameters of movement apply to total ankle replacement, but even more importantly, decreased mobility of the total ankle replacement transforms it into a constrained construct, increasing undesirable stresses across the bond between prosthesis and bone. Although the design of the Agility prosthesis permits a total of 60 of motion [14], any total ankle replacement should attempt to achieve at least the normal range of motion that occurs during walking, which is approximately 24 [29]. As Alvine noted [14], the success of such a procedure probably should not be measured in comparison with a normal joint. Full range of motion after a total ankle replacement is unlikely and probably is not necessary because 20 – 25 of ankle motion facilitates walking without a limp on a level surface and relieves stresses on the adjacent joints and the interface between the implant and host bone [30].
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Factors predisposing to postoperative stiffness—an approach to the problem Preoperative factors and ankle motion One of the most critical factors affecting the postoperative range of motion is a pre-existing contracture, which is almost always present with post-traumatic arthritis. The soft tissue envelope around the post-traumatic and arthritic ankle joint is usually scarred, and at times significantly so. Long periods of immobilization leading to tendon contractures, chronic pain syndromes, inadequate rehabilitation, and secondary osteophyte formation further adversely affect ankle joint mobility. In these patients, we have found it more difficult to obtain a satisfactory range of motion even intraoperatively, despite an aggressive soft tissue release. One should be able to recognize preoperatively that with severe ankle ankylosis, an acceptable range of motion may not be attainable. For these patients, arthrodesis may not be perceived as disabling (compared with those who have reasonable but painful motion preoperatively). The authors always carefully evaluate the patient preoperatively to identify the true range of motion of the ankle joint. Clinical examination may reveal what seems to be adequate range of ankle joint motion, but this may actually represent mobility of the transverse tarsal joints. We therefore routinely use dynamic lateral plantarflexion and dorsiflexion views of the ankle during the preoperative evaluation (Fig. 1). These radiographs clearly identify exactly where the sagittal plane motion is occurring. Another important issue during the preoperative evaluation of a stiff arthritic ankle is the adequate assessment of any gastrocnemius-soleus tightness. This is best done using the Silverskjold test. With the patient seated in front of the examiner, the knee is brought to full extension. Then the foot is supinated and dorsiflexed. The amount of dorsiflexion is estimated, and then the knee is flexed to 90 and the foot is again supinated and dorsiflexed. If there is an increase in dorsiflexion with the knee flexed, there is a gastrocnemius contracture. If the knee flexion does not increase the amount of dorsiflexion, then gastrocnemius-soleus tightness is diagnosed. This is not as accurate as in the patient with unrestricted ankle motion, because osteophytes in the arthritic ankle mechanically block dorsiflexion. In such a case, the test is repeated intraoperatively after thorough removal of any osteophytes and the decision for any lengthening is made at that time. Anecdotally, the authors find that we lengthen the Achilles tendon in most patients undergoing total ankle replacement. The preoperative evaluation regarding the range of motion is completed by evaluating the mobility of the adjacent joints. This has particular relevance with respect to the talonavicular and subtalar joint, because stiffness with or without arthritis in these joints will likely adversely affect the outcome of ankle arthroplasty. Intraoperative factors affecting range of motion Attention to intraoperative details is important to maintain the potential postoperative range of motion after a total ankle replacement. After the skin
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Fig. 1. (A) Plantarflexion and (B) dorsiflexion preoperative views of an arthritic ankle. Note the presence of talar neck and anterior tibial lip osteophytes causing impingement and reducing dorsiflexion.
incision, the extensor retinaculum is carefully incised to create two flaps for adequate repair at the end of the procedure. The retinaculum functions as an important pulley for the tibialis anterior, and if not tensioned will lead to a bowstring effect of the tendon in the subcutaneous tissues, which will affect the power and excursion of ankle dorsiflexion. Careful and adequate distraction with the joint in the neutral position using an external fixator will stretch the contracted soft tissue envelope around the ankle joint, restoring the appropriate length of ligaments and capsule. It is important to avoid overdistraction of the joint, because this leads to inadequate bone removal with subsequent ‘‘overstuffing’’ of the joint and inevitable stiffness. Intraoperative determination of the deltoid endpoint is useful to evaluate the amount of distraction. Once the desired distraction has been achieved, it should still be possible to manually distract the joint using an osteotome as a lever to feel a firm endpoint of the medial collateral ligament.
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Insufficient distraction of the joint results in an inadequate soft tissue envelope, and excessive bone will be removed from the talus or the tibia. Because the prosthesis is inserted deeply into the joint and the malleoli retain their position, the malleoli will abut inferiorly and cause impingement, stiffness, and pain. Clearly, excessive bone removal is precarious, with an increased risk for subsequent subsidence and secondary impingement. Adequate removal of any scar tissue and hypertrophic synovium from the anterior aspect of the joint and the gutters is of great importance to enhance the potential for increased range of motion postoperatively. Following the bone cuts, the posterior aspect of the joint is easily visualized, but complete debridement must be performed. Perhaps even more important is adequate debridement of the medial and lateral joint gutters, with a chamfer cut on the talus to prevent later impingement. Although there are times at which it may be desirable to remove more of the tibia as compared with the talus, this may lead to proximal translation of the center of rotation of the ankle, functional lengthening of the gastrocnemius and soleus, and decreased plantar flexion. Additionally the tips of the malleoli, which remain in their anatomic position, abut against the corners of the proximally translated talus, creating a mechanical block. Finally, seating of the tibial component on the softer metaphyseal bone may lead to later subsidence and secondary impingement, which interferes with the range of motion. Jig positioning distal to the appropriate site leads to a distal translation of the joint line and the center of rotation with subsequent overtensioning of the gastrocnemius-soleus complex. This results in decreased dorsiflexion. For these reasons, seating the talar component too distal may be even worse than too proximal as a result of the subsidence and secondary impingement associated with distal positioning. Liberal use of fluoroscopy and use of an unmounted saw blade through the cutting jig slots are mandatory to avoid misplacement of the bone cuts. After the cuts have been completed and the appropriate size trial prosthesis has been inserted, the range of motion of the ankle joint should be assessed before insertion of the final prosthesis. This step helps determine whether there is any residual bony impingement or stiffness. In the presence of bone loss (such as with revision surgery or avascular necrosis of the distal tibia or talus) that leads to less than optimal implant positioning with respect to the original joint line, a polyethylene component 2 mm thicker than the usual component is used to avoid impingement. At that point the Silverskjold test is repeated, and either a gastrocnemius recession or a percutaneous lengthening of the Achilles tendon is done using a triple hemi section step-cut (Hoke) technique. If the desired range of motion (usually of dorsiflexion) has not been obtained, then the surgeon should proceed to correct this. The components are removed, and careful stripping of the posterior capsule from the distal tibia is performed. With the trial prosthesis in place, the foot is brought into dorsiflexion and the posterior oblique portion of the deltoid ligament is palpated just posterior to the medial malleolus using a small curved osteotome. If it is felt to be tight, it is gently released to further improve the amount of dorsiflexion. The authors find it
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useful to estimate the amount of contracture of the posterior soft tissues by evaluating the range of motion of the joint under fluoroscopy. Uneven joint motion with opening of the anterior aspect of the joint like an open book during plantarflexion implies some residual imbalance or posterior tightness and must be corrected. The size of the prosthesis clearly affects motion, and the authors have changed the prosthesis size when necessary. This is particularly the case when there is an ‘‘in-between’’ size. When adequate motion is not obtained, the authors downsize the prosthesis in an effort to improve the range of motion. The surgeon should select the smaller prosthesis only if it adequately covers the cortical rims of talus and distal tibia, however, and provides sufficient clearance of the malleoli from the talar body, thus preventing late component subsidence and impingement, respectively. If motion is still restricted, then further bone cuts may be made. Here the authors prefer to remove another 1 –2 mm from the talus, although this depends on the available bone in the distal tibia and the talus. If more bone is to be removed from the talus, the amount of bone to be removed should be projected fluoroscopically to ensure that the posterior subtalar joint is not compromised. Any further cuts on the talus must therefore be made with the ankle fully dorsiflexed. Postoperative factors affecting range of motion Initial splinting of the ankle joint in slight dorsiflexion is essential to avoid creating an equinus contracture, because dorsiflexion is difficult to regain later on. Early initiation of range of motion exercises is recommended. The authors use a fracture boot locked in extension to immobilize the joint during the periods when exercise is not performed. Control of postoperative swelling minimizes patient discomfort and increases the ability to perform exercises. Although the authors now use a continuous passive motion device postoperatively, we cannot determine at this stage whether there is any significant advantage to its routine use. The bearing of weight is contraindicated, but we permit the patient to begin swimming and walking in a pool once the incisions are fully healed. Progressive resistance exercises are gradually added to the postoperative rehabilitation regimen. Although severe pain is rare, one should recognize and treat any such pain that could develop into a sympathetically mediated chronic pain syndrome. Early protected weightbearing, pool therapy, and avoidance of prolonged periods of immobilization are crucial. If the syndrome occurs postoperatively, aggressive treatment using range of motion exercises, protected weightbearing, lumbar sympathetic blocks, and various medication programs are initiated. Postoperative heterotopic bone formation can be a significant problem in some patients and may cause severe restriction of motion (Fig. 2). The authors do not have any personal experience with the use of bone wax, although some surgeons have used this routinely to apply to the exposed cut surfaces of the talus. If not recognized, heterotopic bone formation can severely limit motion, requiring
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Fig. 2. Postoperative heterotopic bone formation. The ankle is fixed in slight equinus.
revision, removal, and exchange of the prosthesis, and aggressive removal of the periarticular bone.
Biomechanics and prosthetic design characteristics affecting implant stability Adequate mechanical support and bonding between the host bone and implant are fundamental to the success of total ankle replacement. Unfortunately, the biomechanics of the ankle joint present a unique set of challenges for arthroplasty surgery [31]. The axis of rotation is not constant, but rather is a dynamic entity that changes during motion [28]. Stauffer et al reported that the compressive forces of the ankle reach approximately 5.5 times body weight during normal gait [29]. Additionally, these forces are not consistently perpendicular to the prosthesis but, depending on the variability of human activity and the instant axis of rotation, may be angular or shearing at the prosthesis base plate and the implant-host bone interface, respectively. Hvid et al [32] studied the bone strength of the ankle joint and reported marked reduction in subchondral bone strength as sections were taken farther from the articular surface. They concluded that the residual tibial surface might be too weak to support the loads imposed by the implants. Alvine [14] refers to a similar study in which it was found that the subchondral bone has an elastic modulus of 300 –450 MPa. After removal of 1 cm of subchondral bone, compressive resistance was lowered 30% –50% [14]. Another interesting point reported by Hvid et al is the eccentricity of the area of maximal bone strength of the distal tibia. According to his description, there is a threefold to fourfold increase in the compressive resistance of the subchondral bone in the medial aspect of the distal tibia compared with that of the lateral aspect [32]. The designs of the second-generation implants have been markedly improved in an effort to address these challenges. The phase-five version of the Agility prosthesis has a semi-constrained two-component design that allows for changes
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in the axis of motion and medial-lateral shifting, minimizing side impact and shearing forces that predispose to loosening [33]. The tibial component is metalbacked, which reduces the compressive stresses in the distal tibial subchondral bone by 25% and also reduces shear stresses as compared with an all-polyethylene component [34]. Enlargement of the posterior rim of the tibial component, widening of the base of the talar component, and development of a wider variety of the available sizes of implants has markedly improved the biomechanic environment of the prosthesis. There is more effective transfer of loads from prosthesis to bone through a more extensively covered subchondral bone. There is now more adequate support of the prosthesis on the cortical rim of the distal tibia and proximal talus [33]. The most unique characteristic of the Agility prosthesis, however, is that it takes advantage of arthrodesis of the distal tibiofibular syndesmosis. This fusion converts a three-bone joint to a two-bone joint, which theoretically should simplify the mechanical loads about the ankle joint. The arthrodesis also eliminates the normal fibular motion during gait, which is a potential source of shearing forces across the implant-bone interface [33]. Finally, successful tibiofibular arthrodesis leads to maximum expansion of the surface area for support of the tibial component. A considerable decrease of load per unit area is achieved by expanding the supportive surface, an extremely important consideration for the lateral aspect of the ankle joint, where the subchondral bone strength is normally considerably reduced [32]. Obviously, these design improvements can only be maximized with an appropriate surgical technique.
Clinical and radiographic implications of unsuccessful distal tibiofibular fusion—a modified approach to enhance the rate of healing Careful preparation of the tibiofibular syndesmosis and adequate fixation is of great importance to enhance the potential for healing. Pyevich et al [26] reported that 29% of the patients in their series had a delayed union (radiographic union was not apparent by 6 months), and 9% had a nonunion. The authors have found that delayed union or nonunion of the syndesmosis correlates with radiographic changes of the tibial component position and ballooning lysis (a radiolucent area greater than 2 mm in width) at the interface between the bone and the implant. Pyevich et al [26] also reported that 8 out of the total 12 migrated tibial components in their series were associated with a delayed union or nonunion. The incidence of ballooning lysis in ankles with a nonunion was significantly higher than that in the ankles with a delayed or solid union (P < 0.0001). Similarly, the incidence of ballooning lysis in the ankles with delayed union was significantly higher than that in the ankles with a solid union (P < 0.05) [26]. This lysis almost always occurs at the interface between the fibula and the prosthesis and probably represents bone absorption in an area of high shear stresses that result from continuous motion of the fibula. One can assume that this bone absorption may adversely affect the stability of the tibial component because it reduces the supportive surface of the component with a
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Fig. 3. (A) Severe post-traumatic ankle arthritis with valgus deformity caused by malunion and avascular necrosis of the distal tibial subchondral bone. (B) A medial closing wedge supramalleolar osteotomy was used to correct the deformity. Note that the ankle joint line is parallel to the ground. (C) A total ankle replacement was performed as a staged procedure. (D) Plantarflexion and (E) dorsiflexion views demonstrating good range of motion.
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Fig. 3 (continued).
subsequent increase in the load per unit area. These radiographic data emphasize the importance of syndesmotic arthrodesis, which may be seen as an important factor in component survival with further follow up of this patient group [33]. The authors had noted similar clinical and radiographic problems with syndesmosis fusion failure and modified our approach to fusion. In a 5-year period (1996 to September 2000), the authors performed 134 Agility total ankle replacements, using the recommended method of Alvine [14] for the syndesmosis arthrodesis. Our incidence of delayed and nonunion during that period was 32% (unpublished results). After September 2000 we modified our previous approach to this joint, which had been through a single anterior incision to expose and prepare the distal tibiofibular syndesmosis. We instead inserted a five-hole semi-
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Fig. 4. Avascular necrosis of the talus after a talar neck fracture treated with open reduction and internal fixation. Note the varus deformity in the (A) anteroposterior view and the degenerative arthritis of the talonavicular joint in the (B) lateral view. (C) Anteroposterior and (D) lateral views showing satisfactory alignment of the prosthesis. A talonavicular fusion and a biplane calcaneal osteotomy were performed at the time of the prosthetic implantation.
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Fig. 4 (continued).
tubular plate on the lateral aspect of the fibula using two screws for fixation. Between September 2000 and February 2002, 72 total ankle replacements were implanted, and with the modification of Alvine’s technique described later, the authors have identified 4/72 patients (5%) with a delayed union or nonunion of the syndesmosis (unpublished results). Through the anterior exposure and after adequate removal of the hypertrophic joint capsule, the tubercle of Chaput is used as a landmark to identify the level of the syndesmosis, especially in cases in which the presence of osteophytes and scar tissue has altered the local anatomy. A periosteal elevator is used to expose the anterior aspect of the fibula up to a level 6 cm above the joint line. A rongeur is used to remove the anterior tibiofibular ligament and is then inserted into the syndesmosis. This step is performed taking into account the orientation of the syndesmosis level, which lies slightly obliquely to the coronal plane from anterolateral to posteromedial. By a gentle twisting of the rongeur and levering against the tibia, the syndesmosis is gradually loosened. A laminar spreader is inserted proximal to the ankle joint level at the interosseous space, and the syndesmosis is further distracted. Flexible chisels are used for aggressive decortication and roughening of the bony surfaces up to 2 cm proximal to the tibiofibular groove. After insertion of the tibial component, the plate is inserted laterally onto the fibula through a 2-cm incision and only the middle holes are used. Two fully threaded cancellous screws purchase all four cortices, positioned just above the fin of the tibial component. Cancellous bone graft from the resected tibia and talus is inserted to fill the area of the tibiofibular groove before compressing the plate. With these modifications, the authors are able to avoid unnecessary soft tissue stripping on the lateral side of the fibula. As the screw heads engage the plate,
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Fig. 5. Severe rheumatoid arthritis with valgus ankle joint and flatfoot deformity treated with triple arthrodesis and total ankle replacement as a staged procedure. (A) Anteroposterior and (B) lateral views after the triple arthrodesis. Note the severe valgus deformity of the ankle joint. (C) Postoperative anteroposterior and (D) lateral views of the total ankle performed 3 months later. Note the lateral displacement of the talar component and the medial displacement calcaneal osteotomy performed at the time of the prosthetic implantation.
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Fig. 5 (continued).
there seems to be a considerable compression effect across the total length of the syndesmosis. Additionally, the plate acts as a buttress preventing any springing of the fibula below the level of the screw insertion. The authors are now able to more aggressively decorticate the fibula without the fear of fibular fracture. If a fracture should occur, the plate can easily maintain the stability of the fibula. Finally, a laterally malpositioned prosthesis that causes widening of the syndesmosis during insertion of the prosthesis may adversely affect the healing of the syndesmosis. Lateral translational malposition of the tibial component can occur when trying to minimize the medial bone cut. The fin is precisely positioned on the cutting jig, and theoretically lateral translation malposition should not occur if the cuts are carefully planned and the correct prosthesis size is selected. In our clinical experience, however, the authors have sometimes found that the mediolateral position of the component is not ideal, though the procedure was done in accordance with guidelines. This problem commonly occurs if a conservative initial medial cut is made. To avoid this pitfall, we do not cut the slot for the fin of the tibial component during the initial bone cut. Careful templating of a trial tibial component over the initial bone cuts indicates whether further medial or lateral displacement is necessary, and then any complementary cuts and the fin slot are completed freehand.
Force in the normal and prosthetic ankle—implications of mechanical malalignment and ligament imbalance Several studies using mathematical models [35] or force analysis methods on normal volunteers during normal gait [29] have shown that compressive forces of the normal ankle joint during normal gait are greater than five times body weight.
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Fig. 6. (A) Preoperative radiograph of an arthritic ankle joint. Note the varus deformity mainly below the ankle joint. (B) Lateral view of a total ankle replacement with a concomitant subtalar arthrodesis performed at another institution. The deformity recurred, and a revision was performed at the same institution. (C) Anteroposterior and (D) lateral views of the revised total ankle replacement. Note the oblique cut on talus caused by inadequate medial soft tissue release and the calcaneal osteotomy involving only a small part of the tuberosity and providing inadequate correction. The deformity recurred immediately in the postoperative period. (E) Anteroposterior and (F) lateral radiographs of the second revision procedure at our institution. Note the excellent alignment of the prosthesis after revision cut of the talus, medial displacement of the talar component, revision of the calcaneal osteotomy, and lateral ligament reconstruction.
Demottaz et al [16] reported that in a group of patients with total ankle replacement and documented muscle weakness, the forces in the ankle joint were reduced but were still approximately three times greater than body weight. During normal gait, a tangential or shear force is generated across the ankle joint as a result of the combination of internal tendon forces and the external inertial forces of the body moving over the foot [29]. Hvid et al [32] documented that the distal tibial subchondral bone strength is eccentric and that the compressive force vector is often eccentric. The human ankle joint has a large surface area of approximately 12 cm2. Depending on the prosthetic design, the contact area for implant support is approximately one half of the available total surface area of the ankle joint. For a given load, reducing the area of support increases the load per unit area, so that the normal forces across the prosthetic ankle joint during ambulation are high. This increased magnitude of the normal force in the ankle joint, the variety of joint vectors, and the small area of its application place the implant-host bone
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Fig. 6 (continued).
area under considerable loads. Even a slight degree of mechanical malalignment leads to a higher rate of failure. A high eccentric force consistently placed on the tibial component leads to increased moment arm with a tendency for proximal displacement on one side and a corresponding lift-off on the other side. Depending on the strength of the subchondral bone, this subsequently leads to subsidence
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Fig. 6 (continued).
or micromotion. Micromotion in excess of 150 mm prevents bony ingrowth into the prosthesis and leads to a high rate of failure [36]. Any malalignment in the coronal plane can also lead to line loading (force transmitted to the fixed polyethylene bearing along an edge of the talar component), which accelerates the rate of polyethylene wear with subsequent increased production of wear particles. The inflammatory reaction triggered by these particles eventually leads to considerable osteolysis and increased risk for revision surgery [37]. Another important issue with respect to the Agility implant is that the locking mechanism for the polyethylene insert does not have the expanded surface area for improved locking, as seen with the new designs of hip and knee implants. This potentially leads to increased contact stresses on the polyethylene, especially in the presence of mechanical malalignment, and subsequent wear [38]. Unbalanced ligament tensioning is another concern. In a chronically deformed ankle, collateral ligaments at the apex of the deformity are usually insufficient and the ligaments on the opposite side are contracted. The talus not only dorsiflexes and plantarflexes, but also internally rotates approximately 10 during gait. Controlled motion in the sagittal plane, rotation, and joint stability during gait are provided by balanced ligamentous restraint. Clearly the unbalanced ligaments of the chronically deformed ankle alter the normal kinematics of the joint, inducing abnormal forces across the implant-host bone interface.
Correction of foot and ankle deformity during a total ankle replacement The surgeon should reconstruct the ankle joint by placing the prosthesis parallel to the ground. Adequate soft tissue balancing and complete ankle and
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hindfoot alignment are crucial. Planning the correction of a deformity starts with thorough preoperative clinical and radiographic evaluation. Understanding of the mechanical axis is critical. If there is a significant varus or valgus deformity in the hip or knee, even a well aligned ankle prosthesis will not be ideal if these deformities were subsequently corrected. The patient is observed standing to identify the presence of any obvious mechanical malalignment. A malaligned knee, the presence of tibia vara, or other deformity from a previous fracture malunion are recorded. If necessary, full-length weightbearing radiographs of the lower extremity are obtained to further evaluate the mechanical axis. The patient is also observed walking with and without footwear to evaluate any tendency for instability or malalignment, especially at the ankle and hindfoot. Additionally, any gait abnormalities or compensatory mechanisms used by the patient to improve the gait are recorded. The whole lower extremity is also assessed to determine the active and passive range of motion of hip, knee, and foot and ankle joints. A total ankle replacement cannot compensate for a lack of motion in the joints above and below it. If foot and ankle deformity is present, the surgeon identifies whether these deformities are passively correctable and to what degree they are correctable. For example, in a patient with a varus ankle, the hindfoot attempts to compensate by increasing valgus. Reducing and stabilizing the ankle deformity, the surgeon should evaluate whether the hindfoot remains in valgus or is reduced to a plantigrade position. Unfortunately, there are cases in which the deformity in the tibiotalar joint itself is fixed and it is difficult to adequately determine the plantigrade position of the hindfoot. The ankle joint is manually assessed for the presence or absence of ligament instability, and the motor strength of the major muscle groups is also carefully recorded. Standing radiographs of the ankle are obtained, and in the presence of deformity additional stress views are obtained to determine if the deformity is correctable and to what degree. Stress views also provide significant information for the status of the ligaments on the opposite side of the deformity. In cases with hindfoot deformity, a modified Buck view is obtained, which provides adequate information regarding the degree of malalignment through the subtalar joint. Standard ankle radiographs are evaluated for the presence and degree of degenerative changes in the adjacent joints. Any radiographic findings with concomitant clinical findings suggesting involvement of other joints in the degenerative process should be taken into account in planning any other procedures in addition to the ankle replacement. Patients with significant mechanical malalignment of the knee or tibia should be considered for reconstructive procedures of these deformities before a total ankle replacement. For example, the authors would routinely perform a supramalleolar osteotomy as a staged procedure before a total ankle replacement where necessary (Fig. 3). Most additional procedures below the ankle joint can be performed simultaneously with the ankle replacement or as a staged procedure. As a generalization, the authors prefer to preserve foot flexibility and to avoid hindfoot arthrodesis. If staged procedures are indicated, the intervals between them and the ankle
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Fig. 7. Preoperative (A) anteroposterior and (B) lateral views of a patient with cavovarus deformity. (C) Postoperative anteroposterior view of the same patient showing excellent alignment of the prosthesis. Note the medial displacement of the talar component. (D) Lateral view of the same patient. Because of severe deformity, a biplane calcaneal osteotomy and a modified Chrisman-Snook procedure were performed at the time of prosthetic implantation.
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Fig. 7 (continued).
replacement should be reduced to avoid osteopenia that may jeopardize future implant support. There are valid reasons to perform the surgery simultaneously, such as to avoid the stiff fibrosis of the soft tissues following staged procedures. Generally, however, the authors wait approximately 3 months. The authors perform a talonavicular or a subtalar arthrodesis at the same time as the ankle replacement (Fig. 4), whereas a triple arthrodesis is performed as a staged procedure approximately 3 – 6 months before the ankle replacement. The triple arthrodesis is done to adequately correct any hindfoot and midfoot deformities and to create a plantigrade foot (Fig. 5). This restores more normal bone anatomy, which minimizes incorrect cuts especially on the talus. For example, in the presence of a severe acquired flatfoot deformity, trying to make the horizontal cut on the talus, which has an increased declination angle, leads to unnecessary increased bone resection from its posterior aspect and potential inadvertent entry into the posterior facet of the subtalar joint. In the case of varus ankle deformity, a wide spectrum of pathology ranges from a slightly deformed ankle joint with minimal soft tissue contracture to a severely deformed cavovarus foot and ankle with lateral ligament and peroneus brevis insufficiency. Depending on the severity and the nature of the deformity, one must address the contracted deltoid ligament, lateral ankle ligament insufficiency, motor deficit of the peroneus brevis, focal bone loss on the medial aspect of the distal tibial articular surface, varus heel, and medially displaced Achilles tendon. The first step during correction of the varus deformity is adequate restoration of the soft tissue length using the external fixator, inserted perpendicular to the plane of the deformity. With the foot in a plantigrade position, gradual distraction is applied to restore adequate soft tissue length. The clear space created should be rectangular and not trapezoidal, which would lead to an oblique cut of the talus.
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The surgeon should resist the temptation to perform such a cut to compensate for any residual medial contracture because this leads to altered kinematics of the ankle, generating undesirable forces across the contact surfaces. Additionally, because the medial structures remain stiff, the residual varus moment will lead to recurrent deformity, regardless of any other procedures performed (Fig. 6). Usually the deltoid ligament is contracted, at times markedly so, and a release is required. The authors perform the release through the joint in a stepwise fashion, trying to identify which part of the ligament is responsible for the deformity. The deep portion is initially released, and then the other portions are palpated and sequentially released while a valgus force is applied to the ankle. After adequate medial release, the efficiency of the lateral structures is assessed. If necessary, a nonanatomic lateral ligament reconstruction is performed using the Myerson modification of the Chrisman-Snook procedure [39]. Adequate debridement of the lateral gutter from scar tissue and osteophytes is critical to allow rotation of the talar body in the mortise. In some patients, a slight chamfer cut at the lateral edge of the talar body is required to allow talar rotation. It is actually easier to align the prosthesis where the varus is associated with bone loss on the medial distal tibial plafond. This deformity is corrected by applying the cutting jig perpendicular to the limb axis, thereby removing slightly more bone from the lateral than the medial distal tibia. If the preoperative varus
Fig. 8. (A) Preoperative anteroposterior view of an arthritic ankle with valgus deformity. (B) Excellent alignment of the prosthesis after adequate soft tissue balancing and lateral displacement of the talar component.
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deformity is more marked, then the talar component is positioned slightly more medially on the talar body. This displacement lateralizes the ground reaction force pushing the ankle into valgus and compensating for any residual varus moment. Here the authors also use a revision talar component with its broader base, increasing the contact area with the talus. Finally, a lateral displacement calcaneal osteotomy is done to alter the weightbearing axis and the ground reaction force. The translated tuberosity also moves the Achilles tendon laterally, removing its inverting effect (Fig. 7). In cases of more severe cavovarus deformity with an increased pitch angle of the calcaneus, proximal translation of the calcaneus is added to a biplanar wedge and lateral translation (a triplane osteotomy). Finally, in these cases of cavovarus deformity, a peroneus longus to brevis tendon transfer is performed. A valgus ankle deformity is associated with a contracted lateral ligament, deltoid ligament insufficiency, a valgus heel, a laterally displaced Achilles tendon that acts as a hindfoot evertor, a shortened and deformed fibula caused by chronic impingement, and spring ligament and posterior tibial tendon rupture. Although the pathologic anatomy is different, the same treatment philosophy applies for the correction of the valgus deformity (Fig. 8). The basic steps include correction of any deformities above and below the ankle before the prosthetic implantation using a variety of procedures (osteotomies, fusions, posterior tibial tendon reconstruction), adequate soft tissue balancing using an external fixator, lateral displacement of the talar component, medial displacement calcaneal osteotomy, and use of the broad-based revision talar component in cases with more severe deformity. Perhaps the most significant issue in the correction of the valgus deformity is the completely torn or severely stretched deltoid ligament. When the deltoid ligament is completely torn, adequate reconstruction can be performed only by using a tendon graft. We use a hamstring allograft for this procedure. When the ligament is present but attenuated, it is carefully mobilized and the bone surface on the medial malleolus is roughened. The ligament is then reattached with the proper tension using suture anchors. One must be careful with correction of the valgus ankle deformity, and staged correction of the hindfoot may be prudent for some of these patients.
Summary The design of the Agility total ankle replacement (DePuy, Warsaw, IN) has improved in an effort to address the biomechanic challenges of the ankle joint. Certainly further laboratory investigation and clinical trials with ankle replacement are needed to improve its position as the major alternative to ankle arthrodesis. As the science behind the ankle implants has evolved during the last 15 years, so has our experience and understanding of some crucial factors predisposing to an unsuccessful outcome. Complications such as postoperative stiffness, prosthesis subsidence, and residual deformity along with infection and wound healing
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problems jeopardize a successful outcome. Adequate knowledge of anatomy and biomechanics, careful preoperative evaluation and planning, and strict attention to operative details help minimize the incidence of these complications.
References [1] Coester LM, Saltzman CL, et al. Long-term results following ankle arthrodesis for post-traumatic arthritis. J Bone Joint Surg 2001;83A:219 – 28. [2] Miller SD, Paremain GD, Myerson MS. The miniarthrotomy technique of ankle arthrodesis: a cadaver study of operative vascular compromise and early clinical results. Orthopedics 1996; 19:425 – 30. [3] Paremain GD, Miller SD, Myerson MS. Ankle arthrodesis: results after the miniarthrotomy technique. Foot Ankle Int 1996;17(5):247 – 52. [4] Frey C, Halikus MN, VuRose T, et al. A review of ankle arthrodesis: predisposing factors to nonunion. Foot Ankle Int 1994;15(11):581 – 4. [5] Morrey BF, Wiedeman GP. Complications and long term results of ankle arthrodesis following trauma. J Bone Joint Surg 1980;62A:777 – 84. [6] Mazur JM, Schwartz E, Simon SR. Ankle arthrodesis. Long-term follow-up with gait analysis. J Bone Joint Surg 1979;61A:964 – 75. [7] Takakura Y, Tanaka Y, Kumai T, et al. Low tibial osteotomy for osteoarthritis of the ankle: results of a new operation in 18 patients. J Bone Joint Surg 1995;77B:50 – 4. [8] Graehl P, Hersh M, et al. Supramalleolar osteotomy for the treatment of symptomatic tibial malunion. J Orthop Trauma 1998;1(4):281 – 92. [9] Takakura Y, Takaoka T, Tanaka Y, et al. Results of opening-wedge osteotomy for the treatment of a post-traumatic varus deformity of the ankle. J Bone Joint Surg 1998;80A:213 – 8. [10] Heywood AWB. Supramalleolar osteotomy in the management of the rheumatoid hindfoot. Clin Orthop 1983;177:76 – 81. [11] Pearce M, Smith M, et al. Supramalleolar tibial osteotomy for hemophilic arthropathy of the ankle. J Bone Joint Surg 1994;76B:947 – 50. [12] Van Valburg AA, Van Roermund PM, Lammens J, et al. Can Ilizarov joint distraction delay the need for an arthrodesis of the ankle? A preliminary report. J Bone Joint Surg 1995;77B:720 – 5. [13] Acevedo J, Myerson M. Reconstructive alternatives for ankle arthritis. Foot Ankle Clin 1999; 4(2):409 – 30. [14] Alvine FG. Total ankle arthroplasty. In: Myerson MS, editor. Foot and ankle disorders. Philadelphia: WB Saunders; 2000. p. 1085 – 102. [15] Bolton-Maggs BG, Sudlow RA, Freeman MA. Total ankle arthroplasty. A long-term review of the London Hospital experience. J Bone Joint Surg 1985;67B:785 – 90. [16] Demottaz JD, Mazur JM, Thomas WH, et al. Clinical study of total ankle replacement with gait analysis. A preliminary report. J Bone Joint Surg 1979;61A:976 – 88. [17] Dini AA, Bassett III FH. Evaluation of the early result of Smith total ankle replacement. Clin Orthop 1980;146:228 – 30. [18] Kitaoka HB, Patzer GL, Ilstrup DM, et al. Survivorship analysis of the Mayo total ankle arthroplasty. J Bone Joint Surg 1994;76A:974 – 9. [19] Unger AS, Inglis AE, Mow CS, et al. Total ankle replacement in rheumatoid arthritis: a longterm follow-up study. Foot Ankle 1988;8(4):173 – 9. [20] Buechel FF, Pappas MJ. Survivorship and clinical evaluation of cementless, meniscal bearing total ankle replacements. Semin Arthroplasty 1992;3:43 – 50. [21] Takakura Y, Tanaka Y, Sugimoto K, et al. Ankle arthroplasty: a comparative study of cemented metal and uncemented ceramic prostheses. Clin Orthop 1990;252:209 – 16. [22] Conti SF, Wong YS. Complications of total ankle arthroplasty. Clin Orthop 2001;391:105 – 14. [23] Kofoed H. Cylindrical cemented ankle arthroplasty: a prospective series with long-term followup. Foot Ankle Int 1995;16(8):474 – 9.
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[24] Kofoed H, Sorensen TS. Ankle arthroplasty for rheumatoid arthritis and osteoarthritis: prospective long-term study of cemented replacements. J Bone Joint Surg 1998;80B:328 – 32. [25] Kofoed H, Lundberg- Jensen A. Ankle arthroplasty in patients younger and older than 50 years: a prospective series with long-term follow-up. Foot Ankle Int 1999;20(8):501 – 6. [26] Pyevich MT, Salzmann CL, Callaghan JJ, Alvine FG. Total ankle arthroplasty: a unique design. Two- to twelve-year follow-up. J Bone Joint Surg 1998;80A:1410 – 20. [27] Frankel VH, Nordin M. Biomechanics of the ankle. In: Nordin M, Frankel VH, editors. Basic biomechanics of the musculoskeletal system. 2nd edition. Philadelphia, London: Lea and Febiger; 1989. p. 153 – 61. [28] Lundberg A, Svensson OK, Nemeth G, et al. The axis of rotation of the ankle joint. J Bone Joint Surg 1989;71B:94 – 9. [29] Stauffer RN, Chao EYS, Brewster RC. Force and motion analysis of the normal, diseased, and prosthetic ankle joint. Clin Orthop 1977;127:189 – 96. [30] Wagner F. Ankle fusion for degenerative arthritis secondary to collagen diseases. Foot Ankle 1982;3:24 – 31. [31] Deland JT, Morris GD, Sung IH. Biomechanics of the ankle joint. A perspective on total ankle replacement. Foot Ankle Clin 2000;5(4):747 – 59. [32] Hvid I, Rasmussen O, Jensen NC, et al. Trabecular bone strength profiles at the ankle joint. Clin Orthop 1985;199:306 – 12. [33] Saltzman CL, Alvine FG. The Agility total ankle replacement. Instr Course Lect 2002;51: 129 – 33. [34] Falsig J, Hvid I, Jensen N. Finite element stress analysis of some ankle joint prostheses. Clin Biomech 1986;1:71. [35] Seirig A, Arvikar RJ. The prediction of muscular load sharing and joint forces in the lower extremities during walking. J Biomech 1975;8:89. [36] Volz RG, Nisbet JK, Lee RW, et al. The mechanical stability of various non-cemented tibial components. Clin Orthop 1988;226:38 – 42. [37] Kadoya Y, Kobayashi A, Ohashi H. Wear and osteolysis in total joint replacements. Acta Orthop Scand Suppl 1998;278:1 – 16. [38] Gill LH. Principles of joint arthroplasty as applied to the ankle. Instr Course Lect 2002;51: 117 – 28. [39] Acevedo J, Myerson M. Modification of the Chrisman-Snook procedure. Foot Ankle Int 2000; 21(2):154 – 5.
How to avoid specific complications of total ankle replacement Emmanouil D. Stamatis, MDa, Mark S. Myerson, MDb,* a
Department of Orthopaedic Surgery, The Union Memorial Hospital, Union Memorial Orthopaedics, The Johnston Professional Building, #400, 3333 North Calvert Street, Baltimore, MD 21218, USA b Institute for Foot and Ankle Reconstruction, Mercy Hospital, 301 St. Paul Place, Baltimore, MD 21202, USA
Degenerative arthritis of the ankle joint, whether idiopathic, traumatic, or from a systemic process, presents a significant orthopedic problem. Orthopedic surgeons have traditionally performed ankle arthrodesis, but this procedure is associated with considerable morbidity, potential complications, and long-term adverse effects. It has been assumed that improved arthrodesis techniques would bring improved outcomes, but this has not been the case at all. After arthrodesis, prolonged immobilization leads to a marked loss of subtalar motion, partly from the arthrodesis itself and partly from prolonged immobilization [1]. Although some investigators have reported a high rate of union [2,3], nonunion has been reported in the recent literature as high as 41% [4]. There are also other issues that are not always taken into consideration, including persistent pain and an abnormal gait in a high percentage of patients even after a successful arthrodesis [5]. Perhaps the most important aspect of ankle arthrodesis is not whether fusion occurs, but what the effect of the arthrodesis is on the remaining function of the foot. The increased stress on adjacent joints, with subsequent increased rates of degenerative arthritis, is worrisome [1,6]. Although issues like nonunion are a complication of the procedure itself, other issues occur because adjacent joints are affected by ankle motion limitations. This concern raises questions related to the routine use of ankle arthrodesis in younger patients. Alternative surgical procedures have emerged over the past decade as viable options for the treatment of ankle joint arthritis, including supramalleolar osteotomy, distraction ankle arthroplasty, allograft joint replacement, and total ankle replacement. Supramalleolar osteotomy has played a role in the management of ankle arthritis, particularly in the presence of distal tibial malalignment that was either * Corresponding author. E-mail address: [email protected] (M.S. Myerson). 1083-7515/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S 1 0 8 3 - 7 5 1 5 ( 0 2 ) 0 0 0 5 7 - 8
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idiopathic [7] or secondary to trauma [8,9]. There are also a few reports on the role of the supramalleolar osteotomy for the treatment of other types of arthritis [10,11], but in these limited series the investigators tried to create a plantigrade foot rather than to treat the ankle joint arthritis itself. We have been encouraged by the use of supramalleolar osteotomy at our institution, but we have found that this procedure has a predominant role in the presence of mechanical malalignment. Distraction ankle arthroplasty has been reported by Van Valburg et al [12] as an alternative method of treatment for ankle arthritis. In an earlier report of our experience with this technique [13], our results were disappointing in that most of these patients reported little functional improvement. Since that time we have initiated an alternative method of distraction including the use of fascial interposition arthroplasty; however, the results of this newer technique have yet to be examined. The first total ankle replacement was performed in 1970 by Lord and Marrott [14], but the results were unsatisfactory and the implant was abandoned. Other total ankle implants were released in the early 1970s, but these were all associated with significant complications and long-term unpredictability, and the procedure was abandoned by most surgeons [15 – 19]. Inappropriate patient selection, implant design problems, poor cement technique, lack of adequate and accurate instrumentation, and lack of adequate revision options caused by significant amounts of bone resection during the initial procedure were some of the most significant problems with the first-generation implants. Despite these disappointing results, the deleterious long-term side effects of ankle arthrodesis along with the potential complications refueled the continued search for a reliable implant. The second generation of ankle implants has relied on metallurgy improvements, more sophisticated instrumentation, and a better understanding of ankle joint biomechanics. There has also been a trend for prostheses that use biologic fixation, which has also been shown to give better results than cemented implants [20,21]. Despite these improvements, for many surgeons total ankle replacement remains a complex procedure with an unpredictable outcome. For most surgeons familiar with ankle replacement, this procedure is indicated for patients with low demands and minimal tibiotalar deformity. As noted by Conti and Wong [22], the published results of second-generation ankle replacement systems are limited [20,23 – 26] and the data presented are retrospective and often anecdotal. The science behind the ankle implants has evolved tremendously during the last 15 years, as has the experience and the recognition of the crucial factors predisposing to an unsuccessful outcome. It is now accepted that total ankle replacement is a technically difficult procedure that demands foot and ankle expertise. The learning curve is long and steep, and meticulous attention to detail is required. Complications and intraoperative difficulties with total ankle replacement have been well described, and the possible pitfalls and their solutions have been discussed. After the accumulated experience of the senior author with more than 200 total ankle replacement procedures using the Agility prosthesis (DePuy,
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Warsaw, IN), we have found that many of the technical problems and errors experienced earlier are no longer as much of an issue. The potential successful outcome of this procedure mainly depends on the elimination of complications such as inadequate postoperative range of motion, inadequate fixation of the implant with late subsidence, and inadequate correction of preoperative foot and ankle deformities that create an unfavorable mechanical environment for the prosthesis. Thus, this article focuses on the factors affecting postoperative range of motion, our technique to enhance the union rate of the distal tibiofibular or syndesmosis arthrodesis, and our approach to correction of the varus-valgus deformities of the ankle joint and any other concomitant deformities of the hindfoot and midfoot.
Ankle gait and clinical implications of the stiff total ankle replacement The total range of motion of the ankle joint in the sagittal plane is approximately 45, but there is great variation among patients, because dorsiflexion ranges between 10 and 23 and plantarflexion between 25 and 35 [27]. Several researchers have studied the range of motion of the ankle joint in normal gait and found dorsiflexion averaged 10 and plantarflexion averaged 20 [28]. Stauffer et al [29] reported that the range of motion averaged 24 during normal gait, 10 of this motion dorsiflexion and 14 plantarflexion. Approximately 37 of motion is used for ascending stairs and 56 for descending stairs. Approximately 14 of motion is used in the stance phase of gait, with reduced dorsiflexion mainly affecting the midstance phase and reduced plantarflexion affecting the heel strike and toe-off phases. Interestingly, similar amounts of dorsiflexion and even less plantarflexion are adequate for walking at a pace 50% faster than normal walking speed [29]. Inadequate dorsiflexion during the midstance phase leads to a recurvatum thrust on the knee joint, inadequate propelling of the leg over the foot, an uneven gait, and increased stress concentration across the midfoot. Inadequate plantarflexion leads to increased pressure on the heel during heel strike and weak toe-off. These same parameters of movement apply to total ankle replacement, but even more importantly, decreased mobility of the total ankle replacement transforms it into a constrained construct, increasing undesirable stresses across the bond between prosthesis and bone. Although the design of the Agility prosthesis permits a total of 60 of motion [14], any total ankle replacement should attempt to achieve at least the normal range of motion that occurs during walking, which is approximately 24 [29]. As Alvine noted [14], the success of such a procedure probably should not be measured in comparison with a normal joint. Full range of motion after a total ankle replacement is unlikely and probably is not necessary because 20 – 25 of ankle motion facilitates walking without a limp on a level surface and relieves stresses on the adjacent joints and the interface between the implant and host bone [30].
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Factors predisposing to postoperative stiffness—an approach to the problem Preoperative factors and ankle motion One of the most critical factors affecting the postoperative range of motion is a pre-existing contracture, which is almost always present with post-traumatic arthritis. The soft tissue envelope around the post-traumatic and arthritic ankle joint is usually scarred, and at times significantly so. Long periods of immobilization leading to tendon contractures, chronic pain syndromes, inadequate rehabilitation, and secondary osteophyte formation further adversely affect ankle joint mobility. In these patients, we have found it more difficult to obtain a satisfactory range of motion even intraoperatively, despite an aggressive soft tissue release. One should be able to recognize preoperatively that with severe ankle ankylosis, an acceptable range of motion may not be attainable. For these patients, arthrodesis may not be perceived as disabling (compared with those who have reasonable but painful motion preoperatively). The authors always carefully evaluate the patient preoperatively to identify the true range of motion of the ankle joint. Clinical examination may reveal what seems to be adequate range of ankle joint motion, but this may actually represent mobility of the transverse tarsal joints. We therefore routinely use dynamic lateral plantarflexion and dorsiflexion views of the ankle during the preoperative evaluation (Fig. 1). These radiographs clearly identify exactly where the sagittal plane motion is occurring. Another important issue during the preoperative evaluation of a stiff arthritic ankle is the adequate assessment of any gastrocnemius-soleus tightness. This is best done using the Silverskjold test. With the patient seated in front of the examiner, the knee is brought to full extension. Then the foot is supinated and dorsiflexed. The amount of dorsiflexion is estimated, and then the knee is flexed to 90 and the foot is again supinated and dorsiflexed. If there is an increase in dorsiflexion with the knee flexed, there is a gastrocnemius contracture. If the knee flexion does not increase the amount of dorsiflexion, then gastrocnemius-soleus tightness is diagnosed. This is not as accurate as in the patient with unrestricted ankle motion, because osteophytes in the arthritic ankle mechanically block dorsiflexion. In such a case, the test is repeated intraoperatively after thorough removal of any osteophytes and the decision for any lengthening is made at that time. Anecdotally, the authors find that we lengthen the Achilles tendon in most patients undergoing total ankle replacement. The preoperative evaluation regarding the range of motion is completed by evaluating the mobility of the adjacent joints. This has particular relevance with respect to the talonavicular and subtalar joint, because stiffness with or without arthritis in these joints will likely adversely affect the outcome of ankle arthroplasty. Intraoperative factors affecting range of motion Attention to intraoperative details is important to maintain the potential postoperative range of motion after a total ankle replacement. After the skin
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Fig. 1. (A) Plantarflexion and (B) dorsiflexion preoperative views of an arthritic ankle. Note the presence of talar neck and anterior tibial lip osteophytes causing impingement and reducing dorsiflexion.
incision, the extensor retinaculum is carefully incised to create two flaps for adequate repair at the end of the procedure. The retinaculum functions as an important pulley for the tibialis anterior, and if not tensioned will lead to a bowstring effect of the tendon in the subcutaneous tissues, which will affect the power and excursion of ankle dorsiflexion. Careful and adequate distraction with the joint in the neutral position using an external fixator will stretch the contracted soft tissue envelope around the ankle joint, restoring the appropriate length of ligaments and capsule. It is important to avoid overdistraction of the joint, because this leads to inadequate bone removal with subsequent ‘‘overstuffing’’ of the joint and inevitable stiffness. Intraoperative determination of the deltoid endpoint is useful to evaluate the amount of distraction. Once the desired distraction has been achieved, it should still be possible to manually distract the joint using an osteotome as a lever to feel a firm endpoint of the medial collateral ligament.
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Insufficient distraction of the joint results in an inadequate soft tissue envelope, and excessive bone will be removed from the talus or the tibia. Because the prosthesis is inserted deeply into the joint and the malleoli retain their position, the malleoli will abut inferiorly and cause impingement, stiffness, and pain. Clearly, excessive bone removal is precarious, with an increased risk for subsequent subsidence and secondary impingement. Adequate removal of any scar tissue and hypertrophic synovium from the anterior aspect of the joint and the gutters is of great importance to enhance the potential for increased range of motion postoperatively. Following the bone cuts, the posterior aspect of the joint is easily visualized, but complete debridement must be performed. Perhaps even more important is adequate debridement of the medial and lateral joint gutters, with a chamfer cut on the talus to prevent later impingement. Although there are times at which it may be desirable to remove more of the tibia as compared with the talus, this may lead to proximal translation of the center of rotation of the ankle, functional lengthening of the gastrocnemius and soleus, and decreased plantar flexion. Additionally the tips of the malleoli, which remain in their anatomic position, abut against the corners of the proximally translated talus, creating a mechanical block. Finally, seating of the tibial component on the softer metaphyseal bone may lead to later subsidence and secondary impingement, which interferes with the range of motion. Jig positioning distal to the appropriate site leads to a distal translation of the joint line and the center of rotation with subsequent overtensioning of the gastrocnemius-soleus complex. This results in decreased dorsiflexion. For these reasons, seating the talar component too distal may be even worse than too proximal as a result of the subsidence and secondary impingement associated with distal positioning. Liberal use of fluoroscopy and use of an unmounted saw blade through the cutting jig slots are mandatory to avoid misplacement of the bone cuts. After the cuts have been completed and the appropriate size trial prosthesis has been inserted, the range of motion of the ankle joint should be assessed before insertion of the final prosthesis. This step helps determine whether there is any residual bony impingement or stiffness. In the presence of bone loss (such as with revision surgery or avascular necrosis of the distal tibia or talus) that leads to less than optimal implant positioning with respect to the original joint line, a polyethylene component 2 mm thicker than the usual component is used to avoid impingement. At that point the Silverskjold test is repeated, and either a gastrocnemius recession or a percutaneous lengthening of the Achilles tendon is done using a triple hemi section step-cut (Hoke) technique. If the desired range of motion (usually of dorsiflexion) has not been obtained, then the surgeon should proceed to correct this. The components are removed, and careful stripping of the posterior capsule from the distal tibia is performed. With the trial prosthesis in place, the foot is brought into dorsiflexion and the posterior oblique portion of the deltoid ligament is palpated just posterior to the medial malleolus using a small curved osteotome. If it is felt to be tight, it is gently released to further improve the amount of dorsiflexion. The authors find it
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useful to estimate the amount of contracture of the posterior soft tissues by evaluating the range of motion of the joint under fluoroscopy. Uneven joint motion with opening of the anterior aspect of the joint like an open book during plantarflexion implies some residual imbalance or posterior tightness and must be corrected. The size of the prosthesis clearly affects motion, and the authors have changed the prosthesis size when necessary. This is particularly the case when there is an ‘‘in-between’’ size. When adequate motion is not obtained, the authors downsize the prosthesis in an effort to improve the range of motion. The surgeon should select the smaller prosthesis only if it adequately covers the cortical rims of talus and distal tibia, however, and provides sufficient clearance of the malleoli from the talar body, thus preventing late component subsidence and impingement, respectively. If motion is still restricted, then further bone cuts may be made. Here the authors prefer to remove another 1 –2 mm from the talus, although this depends on the available bone in the distal tibia and the talus. If more bone is to be removed from the talus, the amount of bone to be removed should be projected fluoroscopically to ensure that the posterior subtalar joint is not compromised. Any further cuts on the talus must therefore be made with the ankle fully dorsiflexed. Postoperative factors affecting range of motion Initial splinting of the ankle joint in slight dorsiflexion is essential to avoid creating an equinus contracture, because dorsiflexion is difficult to regain later on. Early initiation of range of motion exercises is recommended. The authors use a fracture boot locked in extension to immobilize the joint during the periods when exercise is not performed. Control of postoperative swelling minimizes patient discomfort and increases the ability to perform exercises. Although the authors now use a continuous passive motion device postoperatively, we cannot determine at this stage whether there is any significant advantage to its routine use. The bearing of weight is contraindicated, but we permit the patient to begin swimming and walking in a pool once the incisions are fully healed. Progressive resistance exercises are gradually added to the postoperative rehabilitation regimen. Although severe pain is rare, one should recognize and treat any such pain that could develop into a sympathetically mediated chronic pain syndrome. Early protected weightbearing, pool therapy, and avoidance of prolonged periods of immobilization are crucial. If the syndrome occurs postoperatively, aggressive treatment using range of motion exercises, protected weightbearing, lumbar sympathetic blocks, and various medication programs are initiated. Postoperative heterotopic bone formation can be a significant problem in some patients and may cause severe restriction of motion (Fig. 2). The authors do not have any personal experience with the use of bone wax, although some surgeons have used this routinely to apply to the exposed cut surfaces of the talus. If not recognized, heterotopic bone formation can severely limit motion, requiring
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Fig. 2. Postoperative heterotopic bone formation. The ankle is fixed in slight equinus.
revision, removal, and exchange of the prosthesis, and aggressive removal of the periarticular bone.
Biomechanics and prosthetic design characteristics affecting implant stability Adequate mechanical support and bonding between the host bone and implant are fundamental to the success of total ankle replacement. Unfortunately, the biomechanics of the ankle joint present a unique set of challenges for arthroplasty surgery [31]. The axis of rotation is not constant, but rather is a dynamic entity that changes during motion [28]. Stauffer et al reported that the compressive forces of the ankle reach approximately 5.5 times body weight during normal gait [29]. Additionally, these forces are not consistently perpendicular to the prosthesis but, depending on the variability of human activity and the instant axis of rotation, may be angular or shearing at the prosthesis base plate and the implant-host bone interface, respectively. Hvid et al [32] studied the bone strength of the ankle joint and reported marked reduction in subchondral bone strength as sections were taken farther from the articular surface. They concluded that the residual tibial surface might be too weak to support the loads imposed by the implants. Alvine [14] refers to a similar study in which it was found that the subchondral bone has an elastic modulus of 300 –450 MPa. After removal of 1 cm of subchondral bone, compressive resistance was lowered 30% –50% [14]. Another interesting point reported by Hvid et al is the eccentricity of the area of maximal bone strength of the distal tibia. According to his description, there is a threefold to fourfold increase in the compressive resistance of the subchondral bone in the medial aspect of the distal tibia compared with that of the lateral aspect [32]. The designs of the second-generation implants have been markedly improved in an effort to address these challenges. The phase-five version of the Agility prosthesis has a semi-constrained two-component design that allows for changes
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in the axis of motion and medial-lateral shifting, minimizing side impact and shearing forces that predispose to loosening [33]. The tibial component is metalbacked, which reduces the compressive stresses in the distal tibial subchondral bone by 25% and also reduces shear stresses as compared with an all-polyethylene component [34]. Enlargement of the posterior rim of the tibial component, widening of the base of the talar component, and development of a wider variety of the available sizes of implants has markedly improved the biomechanic environment of the prosthesis. There is more effective transfer of loads from prosthesis to bone through a more extensively covered subchondral bone. There is now more adequate support of the prosthesis on the cortical rim of the distal tibia and proximal talus [33]. The most unique characteristic of the Agility prosthesis, however, is that it takes advantage of arthrodesis of the distal tibiofibular syndesmosis. This fusion converts a three-bone joint to a two-bone joint, which theoretically should simplify the mechanical loads about the ankle joint. The arthrodesis also eliminates the normal fibular motion during gait, which is a potential source of shearing forces across the implant-bone interface [33]. Finally, successful tibiofibular arthrodesis leads to maximum expansion of the surface area for support of the tibial component. A considerable decrease of load per unit area is achieved by expanding the supportive surface, an extremely important consideration for the lateral aspect of the ankle joint, where the subchondral bone strength is normally considerably reduced [32]. Obviously, these design improvements can only be maximized with an appropriate surgical technique.
Clinical and radiographic implications of unsuccessful distal tibiofibular fusion—a modified approach to enhance the rate of healing Careful preparation of the tibiofibular syndesmosis and adequate fixation is of great importance to enhance the potential for healing. Pyevich et al [26] reported that 29% of the patients in their series had a delayed union (radiographic union was not apparent by 6 months), and 9% had a nonunion. The authors have found that delayed union or nonunion of the syndesmosis correlates with radiographic changes of the tibial component position and ballooning lysis (a radiolucent area greater than 2 mm in width) at the interface between the bone and the implant. Pyevich et al [26] also reported that 8 out of the total 12 migrated tibial components in their series were associated with a delayed union or nonunion. The incidence of ballooning lysis in ankles with a nonunion was significantly higher than that in the ankles with a delayed or solid union (P < 0.0001). Similarly, the incidence of ballooning lysis in the ankles with delayed union was significantly higher than that in the ankles with a solid union (P < 0.05) [26]. This lysis almost always occurs at the interface between the fibula and the prosthesis and probably represents bone absorption in an area of high shear stresses that result from continuous motion of the fibula. One can assume that this bone absorption may adversely affect the stability of the tibial component because it reduces the supportive surface of the component with a
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Fig. 3. (A) Severe post-traumatic ankle arthritis with valgus deformity caused by malunion and avascular necrosis of the distal tibial subchondral bone. (B) A medial closing wedge supramalleolar osteotomy was used to correct the deformity. Note that the ankle joint line is parallel to the ground. (C) A total ankle replacement was performed as a staged procedure. (D) Plantarflexion and (E) dorsiflexion views demonstrating good range of motion.
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Fig. 3 (continued).
subsequent increase in the load per unit area. These radiographic data emphasize the importance of syndesmotic arthrodesis, which may be seen as an important factor in component survival with further follow up of this patient group [33]. The authors had noted similar clinical and radiographic problems with syndesmosis fusion failure and modified our approach to fusion. In a 5-year period (1996 to September 2000), the authors performed 134 Agility total ankle replacements, using the recommended method of Alvine [14] for the syndesmosis arthrodesis. Our incidence of delayed and nonunion during that period was 32% (unpublished results). After September 2000 we modified our previous approach to this joint, which had been through a single anterior incision to expose and prepare the distal tibiofibular syndesmosis. We instead inserted a five-hole semi-
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Fig. 4. Avascular necrosis of the talus after a talar neck fracture treated with open reduction and internal fixation. Note the varus deformity in the (A) anteroposterior view and the degenerative arthritis of the talonavicular joint in the (B) lateral view. (C) Anteroposterior and (D) lateral views showing satisfactory alignment of the prosthesis. A talonavicular fusion and a biplane calcaneal osteotomy were performed at the time of the prosthetic implantation.
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Fig. 4 (continued).
tubular plate on the lateral aspect of the fibula using two screws for fixation. Between September 2000 and February 2002, 72 total ankle replacements were implanted, and with the modification of Alvine’s technique described later, the authors have identified 4/72 patients (5%) with a delayed union or nonunion of the syndesmosis (unpublished results). Through the anterior exposure and after adequate removal of the hypertrophic joint capsule, the tubercle of Chaput is used as a landmark to identify the level of the syndesmosis, especially in cases in which the presence of osteophytes and scar tissue has altered the local anatomy. A periosteal elevator is used to expose the anterior aspect of the fibula up to a level 6 cm above the joint line. A rongeur is used to remove the anterior tibiofibular ligament and is then inserted into the syndesmosis. This step is performed taking into account the orientation of the syndesmosis level, which lies slightly obliquely to the coronal plane from anterolateral to posteromedial. By a gentle twisting of the rongeur and levering against the tibia, the syndesmosis is gradually loosened. A laminar spreader is inserted proximal to the ankle joint level at the interosseous space, and the syndesmosis is further distracted. Flexible chisels are used for aggressive decortication and roughening of the bony surfaces up to 2 cm proximal to the tibiofibular groove. After insertion of the tibial component, the plate is inserted laterally onto the fibula through a 2-cm incision and only the middle holes are used. Two fully threaded cancellous screws purchase all four cortices, positioned just above the fin of the tibial component. Cancellous bone graft from the resected tibia and talus is inserted to fill the area of the tibiofibular groove before compressing the plate. With these modifications, the authors are able to avoid unnecessary soft tissue stripping on the lateral side of the fibula. As the screw heads engage the plate,
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Fig. 5. Severe rheumatoid arthritis with valgus ankle joint and flatfoot deformity treated with triple arthrodesis and total ankle replacement as a staged procedure. (A) Anteroposterior and (B) lateral views after the triple arthrodesis. Note the severe valgus deformity of the ankle joint. (C) Postoperative anteroposterior and (D) lateral views of the total ankle performed 3 months later. Note the lateral displacement of the talar component and the medial displacement calcaneal osteotomy performed at the time of the prosthetic implantation.
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Fig. 5 (continued).
there seems to be a considerable compression effect across the total length of the syndesmosis. Additionally, the plate acts as a buttress preventing any springing of the fibula below the level of the screw insertion. The authors are now able to more aggressively decorticate the fibula without the fear of fibular fracture. If a fracture should occur, the plate can easily maintain the stability of the fibula. Finally, a laterally malpositioned prosthesis that causes widening of the syndesmosis during insertion of the prosthesis may adversely affect the healing of the syndesmosis. Lateral translational malposition of the tibial component can occur when trying to minimize the medial bone cut. The fin is precisely positioned on the cutting jig, and theoretically lateral translation malposition should not occur if the cuts are carefully planned and the correct prosthesis size is selected. In our clinical experience, however, the authors have sometimes found that the mediolateral position of the component is not ideal, though the procedure was done in accordance with guidelines. This problem commonly occurs if a conservative initial medial cut is made. To avoid this pitfall, we do not cut the slot for the fin of the tibial component during the initial bone cut. Careful templating of a trial tibial component over the initial bone cuts indicates whether further medial or lateral displacement is necessary, and then any complementary cuts and the fin slot are completed freehand.
Force in the normal and prosthetic ankle—implications of mechanical malalignment and ligament imbalance Several studies using mathematical models [35] or force analysis methods on normal volunteers during normal gait [29] have shown that compressive forces of the normal ankle joint during normal gait are greater than five times body weight.
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Fig. 6. (A) Preoperative radiograph of an arthritic ankle joint. Note the varus deformity mainly below the ankle joint. (B) Lateral view of a total ankle replacement with a concomitant subtalar arthrodesis performed at another institution. The deformity recurred, and a revision was performed at the same institution. (C) Anteroposterior and (D) lateral views of the revised total ankle replacement. Note the oblique cut on talus caused by inadequate medial soft tissue release and the calcaneal osteotomy involving only a small part of the tuberosity and providing inadequate correction. The deformity recurred immediately in the postoperative period. (E) Anteroposterior and (F) lateral radiographs of the second revision procedure at our institution. Note the excellent alignment of the prosthesis after revision cut of the talus, medial displacement of the talar component, revision of the calcaneal osteotomy, and lateral ligament reconstruction.
Demottaz et al [16] reported that in a group of patients with total ankle replacement and documented muscle weakness, the forces in the ankle joint were reduced but were still approximately three times greater than body weight. During normal gait, a tangential or shear force is generated across the ankle joint as a result of the combination of internal tendon forces and the external inertial forces of the body moving over the foot [29]. Hvid et al [32] documented that the distal tibial subchondral bone strength is eccentric and that the compressive force vector is often eccentric. The human ankle joint has a large surface area of approximately 12 cm2. Depending on the prosthetic design, the contact area for implant support is approximately one half of the available total surface area of the ankle joint. For a given load, reducing the area of support increases the load per unit area, so that the normal forces across the prosthetic ankle joint during ambulation are high. This increased magnitude of the normal force in the ankle joint, the variety of joint vectors, and the small area of its application place the implant-host bone
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Fig. 6 (continued).
area under considerable loads. Even a slight degree of mechanical malalignment leads to a higher rate of failure. A high eccentric force consistently placed on the tibial component leads to increased moment arm with a tendency for proximal displacement on one side and a corresponding lift-off on the other side. Depending on the strength of the subchondral bone, this subsequently leads to subsidence
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Fig. 6 (continued).
or micromotion. Micromotion in excess of 150 mm prevents bony ingrowth into the prosthesis and leads to a high rate of failure [36]. Any malalignment in the coronal plane can also lead to line loading (force transmitted to the fixed polyethylene bearing along an edge of the talar component), which accelerates the rate of polyethylene wear with subsequent increased production of wear particles. The inflammatory reaction triggered by these particles eventually leads to considerable osteolysis and increased risk for revision surgery [37]. Another important issue with respect to the Agility implant is that the locking mechanism for the polyethylene insert does not have the expanded surface area for improved locking, as seen with the new designs of hip and knee implants. This potentially leads to increased contact stresses on the polyethylene, especially in the presence of mechanical malalignment, and subsequent wear [38]. Unbalanced ligament tensioning is another concern. In a chronically deformed ankle, collateral ligaments at the apex of the deformity are usually insufficient and the ligaments on the opposite side are contracted. The talus not only dorsiflexes and plantarflexes, but also internally rotates approximately 10 during gait. Controlled motion in the sagittal plane, rotation, and joint stability during gait are provided by balanced ligamentous restraint. Clearly the unbalanced ligaments of the chronically deformed ankle alter the normal kinematics of the joint, inducing abnormal forces across the implant-host bone interface.
Correction of foot and ankle deformity during a total ankle replacement The surgeon should reconstruct the ankle joint by placing the prosthesis parallel to the ground. Adequate soft tissue balancing and complete ankle and
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hindfoot alignment are crucial. Planning the correction of a deformity starts with thorough preoperative clinical and radiographic evaluation. Understanding of the mechanical axis is critical. If there is a significant varus or valgus deformity in the hip or knee, even a well aligned ankle prosthesis will not be ideal if these deformities were subsequently corrected. The patient is observed standing to identify the presence of any obvious mechanical malalignment. A malaligned knee, the presence of tibia vara, or other deformity from a previous fracture malunion are recorded. If necessary, full-length weightbearing radiographs of the lower extremity are obtained to further evaluate the mechanical axis. The patient is also observed walking with and without footwear to evaluate any tendency for instability or malalignment, especially at the ankle and hindfoot. Additionally, any gait abnormalities or compensatory mechanisms used by the patient to improve the gait are recorded. The whole lower extremity is also assessed to determine the active and passive range of motion of hip, knee, and foot and ankle joints. A total ankle replacement cannot compensate for a lack of motion in the joints above and below it. If foot and ankle deformity is present, the surgeon identifies whether these deformities are passively correctable and to what degree they are correctable. For example, in a patient with a varus ankle, the hindfoot attempts to compensate by increasing valgus. Reducing and stabilizing the ankle deformity, the surgeon should evaluate whether the hindfoot remains in valgus or is reduced to a plantigrade position. Unfortunately, there are cases in which the deformity in the tibiotalar joint itself is fixed and it is difficult to adequately determine the plantigrade position of the hindfoot. The ankle joint is manually assessed for the presence or absence of ligament instability, and the motor strength of the major muscle groups is also carefully recorded. Standing radiographs of the ankle are obtained, and in the presence of deformity additional stress views are obtained to determine if the deformity is correctable and to what degree. Stress views also provide significant information for the status of the ligaments on the opposite side of the deformity. In cases with hindfoot deformity, a modified Buck view is obtained, which provides adequate information regarding the degree of malalignment through the subtalar joint. Standard ankle radiographs are evaluated for the presence and degree of degenerative changes in the adjacent joints. Any radiographic findings with concomitant clinical findings suggesting involvement of other joints in the degenerative process should be taken into account in planning any other procedures in addition to the ankle replacement. Patients with significant mechanical malalignment of the knee or tibia should be considered for reconstructive procedures of these deformities before a total ankle replacement. For example, the authors would routinely perform a supramalleolar osteotomy as a staged procedure before a total ankle replacement where necessary (Fig. 3). Most additional procedures below the ankle joint can be performed simultaneously with the ankle replacement or as a staged procedure. As a generalization, the authors prefer to preserve foot flexibility and to avoid hindfoot arthrodesis. If staged procedures are indicated, the intervals between them and the ankle
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Fig. 7. Preoperative (A) anteroposterior and (B) lateral views of a patient with cavovarus deformity. (C) Postoperative anteroposterior view of the same patient showing excellent alignment of the prosthesis. Note the medial displacement of the talar component. (D) Lateral view of the same patient. Because of severe deformity, a biplane calcaneal osteotomy and a modified Chrisman-Snook procedure were performed at the time of prosthetic implantation.
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Fig. 7 (continued).
replacement should be reduced to avoid osteopenia that may jeopardize future implant support. There are valid reasons to perform the surgery simultaneously, such as to avoid the stiff fibrosis of the soft tissues following staged procedures. Generally, however, the authors wait approximately 3 months. The authors perform a talonavicular or a subtalar arthrodesis at the same time as the ankle replacement (Fig. 4), whereas a triple arthrodesis is performed as a staged procedure approximately 3 – 6 months before the ankle replacement. The triple arthrodesis is done to adequately correct any hindfoot and midfoot deformities and to create a plantigrade foot (Fig. 5). This restores more normal bone anatomy, which minimizes incorrect cuts especially on the talus. For example, in the presence of a severe acquired flatfoot deformity, trying to make the horizontal cut on the talus, which has an increased declination angle, leads to unnecessary increased bone resection from its posterior aspect and potential inadvertent entry into the posterior facet of the subtalar joint. In the case of varus ankle deformity, a wide spectrum of pathology ranges from a slightly deformed ankle joint with minimal soft tissue contracture to a severely deformed cavovarus foot and ankle with lateral ligament and peroneus brevis insufficiency. Depending on the severity and the nature of the deformity, one must address the contracted deltoid ligament, lateral ankle ligament insufficiency, motor deficit of the peroneus brevis, focal bone loss on the medial aspect of the distal tibial articular surface, varus heel, and medially displaced Achilles tendon. The first step during correction of the varus deformity is adequate restoration of the soft tissue length using the external fixator, inserted perpendicular to the plane of the deformity. With the foot in a plantigrade position, gradual distraction is applied to restore adequate soft tissue length. The clear space created should be rectangular and not trapezoidal, which would lead to an oblique cut of the talus.
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The surgeon should resist the temptation to perform such a cut to compensate for any residual medial contracture because this leads to altered kinematics of the ankle, generating undesirable forces across the contact surfaces. Additionally, because the medial structures remain stiff, the residual varus moment will lead to recurrent deformity, regardless of any other procedures performed (Fig. 6). Usually the deltoid ligament is contracted, at times markedly so, and a release is required. The authors perform the release through the joint in a stepwise fashion, trying to identify which part of the ligament is responsible for the deformity. The deep portion is initially released, and then the other portions are palpated and sequentially released while a valgus force is applied to the ankle. After adequate medial release, the efficiency of the lateral structures is assessed. If necessary, a nonanatomic lateral ligament reconstruction is performed using the Myerson modification of the Chrisman-Snook procedure [39]. Adequate debridement of the lateral gutter from scar tissue and osteophytes is critical to allow rotation of the talar body in the mortise. In some patients, a slight chamfer cut at the lateral edge of the talar body is required to allow talar rotation. It is actually easier to align the prosthesis where the varus is associated with bone loss on the medial distal tibial plafond. This deformity is corrected by applying the cutting jig perpendicular to the limb axis, thereby removing slightly more bone from the lateral than the medial distal tibia. If the preoperative varus
Fig. 8. (A) Preoperative anteroposterior view of an arthritic ankle with valgus deformity. (B) Excellent alignment of the prosthesis after adequate soft tissue balancing and lateral displacement of the talar component.
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deformity is more marked, then the talar component is positioned slightly more medially on the talar body. This displacement lateralizes the ground reaction force pushing the ankle into valgus and compensating for any residual varus moment. Here the authors also use a revision talar component with its broader base, increasing the contact area with the talus. Finally, a lateral displacement calcaneal osteotomy is done to alter the weightbearing axis and the ground reaction force. The translated tuberosity also moves the Achilles tendon laterally, removing its inverting effect (Fig. 7). In cases of more severe cavovarus deformity with an increased pitch angle of the calcaneus, proximal translation of the calcaneus is added to a biplanar wedge and lateral translation (a triplane osteotomy). Finally, in these cases of cavovarus deformity, a peroneus longus to brevis tendon transfer is performed. A valgus ankle deformity is associated with a contracted lateral ligament, deltoid ligament insufficiency, a valgus heel, a laterally displaced Achilles tendon that acts as a hindfoot evertor, a shortened and deformed fibula caused by chronic impingement, and spring ligament and posterior tibial tendon rupture. Although the pathologic anatomy is different, the same treatment philosophy applies for the correction of the valgus deformity (Fig. 8). The basic steps include correction of any deformities above and below the ankle before the prosthetic implantation using a variety of procedures (osteotomies, fusions, posterior tibial tendon reconstruction), adequate soft tissue balancing using an external fixator, lateral displacement of the talar component, medial displacement calcaneal osteotomy, and use of the broad-based revision talar component in cases with more severe deformity. Perhaps the most significant issue in the correction of the valgus deformity is the completely torn or severely stretched deltoid ligament. When the deltoid ligament is completely torn, adequate reconstruction can be performed only by using a tendon graft. We use a hamstring allograft for this procedure. When the ligament is present but attenuated, it is carefully mobilized and the bone surface on the medial malleolus is roughened. The ligament is then reattached with the proper tension using suture anchors. One must be careful with correction of the valgus ankle deformity, and staged correction of the hindfoot may be prudent for some of these patients.
Summary The design of the Agility total ankle replacement (DePuy, Warsaw, IN) has improved in an effort to address the biomechanic challenges of the ankle joint. Certainly further laboratory investigation and clinical trials with ankle replacement are needed to improve its position as the major alternative to ankle arthrodesis. As the science behind the ankle implants has evolved during the last 15 years, so has our experience and understanding of some crucial factors predisposing to an unsuccessful outcome. Complications such as postoperative stiffness, prosthesis subsidence, and residual deformity along with infection and wound healing
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problems jeopardize a successful outcome. Adequate knowledge of anatomy and biomechanics, careful preoperative evaluation and planning, and strict attention to operative details help minimize the incidence of these complications.
References [1] Coester LM, Saltzman CL, et al. Long-term results following ankle arthrodesis for post-traumatic arthritis. J Bone Joint Surg 2001;83A:219 – 28. [2] Miller SD, Paremain GD, Myerson MS. The miniarthrotomy technique of ankle arthrodesis: a cadaver study of operative vascular compromise and early clinical results. Orthopedics 1996; 19:425 – 30. [3] Paremain GD, Miller SD, Myerson MS. Ankle arthrodesis: results after the miniarthrotomy technique. Foot Ankle Int 1996;17(5):247 – 52. [4] Frey C, Halikus MN, VuRose T, et al. A review of ankle arthrodesis: predisposing factors to nonunion. Foot Ankle Int 1994;15(11):581 – 4. [5] Morrey BF, Wiedeman GP. Complications and long term results of ankle arthrodesis following trauma. J Bone Joint Surg 1980;62A:777 – 84. [6] Mazur JM, Schwartz E, Simon SR. Ankle arthrodesis. Long-term follow-up with gait analysis. J Bone Joint Surg 1979;61A:964 – 75. [7] Takakura Y, Tanaka Y, Kumai T, et al. Low tibial osteotomy for osteoarthritis of the ankle: results of a new operation in 18 patients. J Bone Joint Surg 1995;77B:50 – 4. [8] Graehl P, Hersh M, et al. Supramalleolar osteotomy for the treatment of symptomatic tibial malunion. J Orthop Trauma 1998;1(4):281 – 92. [9] Takakura Y, Takaoka T, Tanaka Y, et al. Results of opening-wedge osteotomy for the treatment of a post-traumatic varus deformity of the ankle. J Bone Joint Surg 1998;80A:213 – 8. [10] Heywood AWB. Supramalleolar osteotomy in the management of the rheumatoid hindfoot. Clin Orthop 1983;177:76 – 81. [11] Pearce M, Smith M, et al. Supramalleolar tibial osteotomy for hemophilic arthropathy of the ankle. J Bone Joint Surg 1994;76B:947 – 50. [12] Van Valburg AA, Van Roermund PM, Lammens J, et al. Can Ilizarov joint distraction delay the need for an arthrodesis of the ankle? A preliminary report. J Bone Joint Surg 1995;77B:720 – 5. [13] Acevedo J, Myerson M. Reconstructive alternatives for ankle arthritis. Foot Ankle Clin 1999; 4(2):409 – 30. [14] Alvine FG. Total ankle arthroplasty. In: Myerson MS, editor. Foot and ankle disorders. Philadelphia: WB Saunders; 2000. p. 1085 – 102. [15] Bolton-Maggs BG, Sudlow RA, Freeman MA. Total ankle arthroplasty. A long-term review of the London Hospital experience. J Bone Joint Surg 1985;67B:785 – 90. [16] Demottaz JD, Mazur JM, Thomas WH, et al. Clinical study of total ankle replacement with gait analysis. A preliminary report. J Bone Joint Surg 1979;61A:976 – 88. [17] Dini AA, Bassett III FH. Evaluation of the early result of Smith total ankle replacement. Clin Orthop 1980;146:228 – 30. [18] Kitaoka HB, Patzer GL, Ilstrup DM, et al. Survivorship analysis of the Mayo total ankle arthroplasty. J Bone Joint Surg 1994;76A:974 – 9. [19] Unger AS, Inglis AE, Mow CS, et al. Total ankle replacement in rheumatoid arthritis: a longterm follow-up study. Foot Ankle 1988;8(4):173 – 9. [20] Buechel FF, Pappas MJ. Survivorship and clinical evaluation of cementless, meniscal bearing total ankle replacements. Semin Arthroplasty 1992;3:43 – 50. [21] Takakura Y, Tanaka Y, Sugimoto K, et al. Ankle arthroplasty: a comparative study of cemented metal and uncemented ceramic prostheses. Clin Orthop 1990;252:209 – 16. [22] Conti SF, Wong YS. Complications of total ankle arthroplasty. Clin Orthop 2001;391:105 – 14. [23] Kofoed H. Cylindrical cemented ankle arthroplasty: a prospective series with long-term followup. Foot Ankle Int 1995;16(8):474 – 9.
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