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Technique Tip: Subtalar Joint Fusion Using a Parallel Guide and Double Screw Fixation
The Journal of Foot & Ankle Surgery 49 (2010) 305–309
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Technique Tip: Subtalar Joint Fusion Using a Parallel Guide and Double Screw Fixation Rick L. Scanlan, DPM 1, Patrick R. Burns, DPM 2, Brandon E. Crim, DPM 3 1
Private Practice, Ankle and Foot Centers of Pittsburgh, Attending, Podiatric Medicine and Surgery Residency Program, University of Pittsburgh Medical Center, Pittsburgh, PA Residency Director, Podiatric Medicine and Surgery Residency Program, University of Pittsburgh Medical Center, Department of Orthopedics, Pittsburgh, PA 3 Resident, University of Pittsburgh Medical Center, Pittsburgh, PA 2
a r t i c l e i n f o
a b s t r a c t
Keywords: arthrodesis calcaneus interfragmental compression lag screw osteosynthesis talus
A wide range of techniques has been described to achieve subtalar (talocalcaneal) arthrodesis using interfragmental screw fixation. In this technical report, we describe a method that enables us to accurately position 2 screws across the subtalar joint in order to achieve arthrodesis between the talus and calcaneus. Careful attention to the tips described in this report should minimize the risk of aberrant placement of the screws while expediting the process of osteosynthesis. Ó 2010 by the American College of Foot and Ankle Surgeons. All rights reserved.
Subtalar joint arthrodesis is a surgical option for patients with pain, instability, or deformity who have failed nonoperative treatment. The goal of any subtalar joint fusion is the elimination of motion of the subtalar joint complex, thus eliminating pain for patients, allowing them to return to their past level of activity (1). Isolated subtalar arthrodesis has been shown to result in good to excellent outcomes with high patient satisfaction, with reported fusion rates with the use of screw fixation often exceeding 90% (1, 2). Arthrodesis can be used in patients with prior trauma, such as calcaneal or talar fracture, resulting in degenerative joint changes (1). Subtalar joint fusion has also been described in patients with primary subtalar degeneration, inflammatory arthropathies, rearfoot coalitions, neuromuscular dysfunction, and following infectious degenerative changes. Subtalar joint arthrodesis can also be useful in residual congenital hindfoot deformities, as well as rearfoot deformities such as rigid pes planovalgus and cavus foot. Arthrodesis also restores hindfoot alignment and improves function (2). Wilson (3) was the first to describe isolated subtalar joint arthrodesis in the English literature, and used the fusion to treat patients with intra-articular damage following calcaneal fracture. Since then, many forms of fixation have been described for fusion of the subtalar joint. Internal screw fixation has become an established form of fixation (4). Accurate placement of screw fixation is imperative because improper
Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Brandon E. Crim, DPM, Resident, University of Pittsburgh Medical Center, UPMC Mercy, c/o Debra Bodner, 1400 Locust Street, Pittsburgh, PA 15219. E-mail address: [email protected] (B.E. Crim).
positioning and application of fixation can lead to poor outcomes affecting the function of the entire lower extremity (5). In this report, the authors share a systematic, reliable, reproducible way to perform a subtalar joint fusion with excellent anatomical placement of screw fixation. Surgical Technique The patient is positioned supine on the operating table with bump placement under the ipsilateral hip for needed internal rotation to properly visualize the lateral aspect of the foot. If the surgeon prefers, a tourniquet can be applied to the ipsilateral thigh for hemostasis. The subtalar joint is approached laterally with an incision, which extends from the tip of the fibula to the calcaneocuboid joint. The distal portion of the incision can be extended to the base of the fourth metatarsal if a triple arthrodesis is being performed (Figure 1). The incision is deepened through the subcutaneous tissue with atraumatic technique, with particular care to avoid the communicating branch of the sural nerve. The extensor digitorum brevis muscle belly is reflected dorsally or distally, and the fatty plug (Hoke’s tonsil) is removed from the sinus tarsi. The subtalar joint is then prepared for fusion using the preferred technique of the surgeon; our preferred technique is curettage with subchondral drilling. It is imperative that all cartilage is removed and healthy bleeding bone is visualized, which is optimal for fusion. A lamina spreader may be used to visualize the medial portion of the subtalar joint for joint preparation. If a talocalcaneal coalition is present, it should be resected in order to prepare the remainder of the joint. Following joint preparation, rearfoot alignment should be inspected and any deformity correction such as heel varus should be performed through osteotomies or bone block
1067-2516/$ – see front matter Ó 2010 by the American College of Foot and Ankle Surgeons. All rights reserved. doi:10.1053/j.jfas.2010.02.017
306
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
Fig. 1. Incision placement for lateral access to the subtalar joint. The incision extends from the tip of the fibula to the calcaneocuboid joint. The incision can be lengthened distally to the base of the fourth metatarsal for a triple arthrodesis.
placement. Bone graft, bone morphogenic protein, and/or plateletrich plasma may also be added to the prepared joint to aid timely fusion. The dorsal surface of the talar neck is then approached using an approximately 2-cm midline incision (Figure 2). This location can be visualized under fluoroscopy using a metal object such as a Freer elevator to locate the proper position. The interval for the incision is located between the tibialis anterior and the extensor hallucis longus tendons. This interval is safe relative to position of the dorsalis pedis artery and deep peroneal nerve, and it is imperative to locate the proper interval between the tibialis anterior and extensor hallucis longus to avoid any neurovascular damage. The skin incision is made, and blunt dissection is then carried down to the neck of the talus. A small portion of the periosteum is removed using a Key elevator in the area of planned screw placement. A guide pin is then inserted from the anterior incision through the neck of the talus, crossing the subtalar joint, into the calcaneus (Figures 3 and 4). Before crossing the posterior facet of the subtalar joint, the foot should be placed in the appropriate position for subtalar fusion. The proper frontal plane positioning of the rearfoot is typically 5 of valgus, which allows motion at the midtarsal joint. It is important to remember that the subtalar joint influences the midtarsal joint, and if placed in varus, the midtarsal joint will remain locked at all times during the gait cycle. Attention must also be paid to obtaining the desired sagittal and transverse plane alignments, which vary depending on the individual patient’s needs and anatomy. Next, proper placement of the guide pin should be verified in multiple planes before application of screw fixation. The lateral image will show proper placement in the sagittal plane, and should show the guide wire clearly crossing the talocalcaneal joint (Figure 4). An anteroposterior (AP) ankle view should show the guide wire properly placed within the talus, whereas a calcaneal axial view should show the wire within the calcaneal body. Although the lateral fluoroscopic image is an advantageous view, the other images can help prevent placement of hardware within problematic areas such as the ankle gutters and tarsal tunnel. Once correct guide pin placement is noted under fluoroscopy, a 6.5-mm partially threaded long thread pattern screw is inserted (Figure 5). This screw is inserted using standard osteosynthesis lag technique, with aggressive countersinking to avoid anterior ankle impingement. Headless screws are also an option so as
Fig. 2. Incision placement for access to the talar neck. Proper location can be verified with a lateral fluoroscopic image before incision. The interval for the incision is between the tibialis anterior and extensor hallucis longus tendons. This interval is a ‘‘safe zone’’ away from the anterior neurovascular bundle, but the soft tissues must be retracted with care.
to prevent anterior ankle impingement. Proper screw placement should include the neck of the talus to the body of the calcaneus, with care taken to avoid violation of the inferior cortex of the calcaneus. Once proper screw placement is noted in all planes, the anterior to posterior guide pin is then advanced until it exits the heel (Figure 6). Using the guide wire, which exits the posterior heel, a parallel drill guide is used for placement of the posterior to anterior screw (Figure 7). Proper screw placement for the posterior to anterior screw should include avoidance of the plantar aspect of the calcaneus, as well as the posterior surface of the calcaneus, which can result in screw prominence against the last of the shoe. The guide wire should cross the posterior facet of the subtalar joint and enter the talar body (Figure 8). A 6.5-mm partially threaded short thread pattern screw should be inserted using standard osteosynthesis lag technique (Figure 9, 10). Aggressive countersinking should be used to prevent screw prominence. With either the anterior to posterior screw, or the posterior to anterior screw, if screw threads are crossing the posterior facet, the surgeon can overdrill the proximal segment so as to convert screw placement to lag by technique. Both guide pins are then removed, and proper fixation and alignment should be noted by direct visualization and image intensification fluoroscopy. The area should be flushed with sterile saline, after which proper layer closure is performed. The lower extremity can then be placed in a posterior splint and managed with avoidance of weight bearing on the operated extremity.
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
307
Fig. 3. Application of guide pin for the anterior to posterior screw through the anterior approach. Before crossing the subtalar joint, the rearfoot should be placed in the proper position for fusion.
Fig. 5. Application of 6.5-mm long thread cannulated screw using standard osteosynthesis technique.
Fig. 4. Fluoroscopic confirmation viewed on lateral projection of proper guide pin placement before application of cannulated screw. An anteroposterior ankle should also be taken before application of the screw to ensure proper placement. The screw should enter the talar neck, and extend into the calcaneal body.
Fig. 6. Following the application of the anterior to posterior screw and confirmation of proper placement with fluoroscopy, the guide pin is advanced through the posterior heel. The guide wire will then be used for the application of the posterior to anterior screw using a drill guide.
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R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
Fig. 7. Application of guide wire for the posterior to anterior screw using the parallel drill guide.
Fig. 9. Application of posterior to anterior screw. A 6.5-mm short thread cannulated screw is being inserted for supplemental fixation.
If a revisional arthrodesis is being performed, all hardware must be removed to access the joint. The presence of infection is a direct contraindication to the application of internal fixation, and can be identified using frozen section microscopy, wherein greater than 5 polymorphonuclear leukocytes per high-power field (400) suggests the presence of infection (6). Once infection has been ruled out, the subtalar joint should be prepared to bleeding, healthy tissue, and bone graft may be warranted if the previous resection resulted in significant bone loss. Application of fixation can then follow the technique described above, and the surgeon may consider adjunctive therapy such as bone stimulation.
compression limits motion, which aids bone union. Screws have become a popular form of fixation for subtalar arthrodesis (4). There is no true consensus in the literature as to the need for 1 or 2 screws, and the orientation of these screws also remains a question of the surgeon’s preference. There are benefits, most notably interfragmental compression, associated with either orientation of screw fixation, from anterior to posterior (talus to calcaneus) or posterior to anterior (calcaneus to talus). The benefits of the anterior to posterior screw include ease of placement, and the ability to use the long thread pattern of a partially threaded screw using lag by design technique. Using the long thread pattern enables the screw’s threads to contact more cancellous bone. Finlay et al (12) demonstrated the importance of maximizing contact between the screw and the bone so as to enhance the pullout strength. In a study by McGlamry and Robitaille (4), the anterior to posterior screw showed a higher torque of insertion and pullout strength/failure load when using a cannulated system when compared with a posterior to anterior placed screw. Torque is important because screws are designed to convert torque to
Discussion Many forms of fixation for subtalar joint arthrodesis have been described, including Kirschner wires, staples, screws, and external fixation (2, 4, 7–11). Although studies have been unable to show how much compression is needed for joint fusion, it is understood that
Fig. 8. Confirmation of proper guide wire placement for posterior to anterior screw. The screw should extend from the posterior calcaneus to the talar body.
Fig. 10. Fluoroscopic confirmation of proper screw placement. The screw will be advanced to prevent posterior screw head prominence.
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
compression. Greater torque of insertion of the anterior to posterior screw leads to greater compression between joint surfaces leading to greater stability. Another advantage of the anterior to posterior screw is the bone stock at the entrance point of the screw has been found to be critical to stable internal fixation; Chapman et al (13) showed that the best screw placement is where the entrance cortex is thickest. For subtalar arthrodesis, this corresponds to the thick dorsal cortex of the calcaneus. Because of the small area of the talar neck, placement of supplemental fixation from anterior to posterior can be difficult. Using the technique described, placement of a short thread pattern partially threaded cannulated screw can be inserted from posterior to anterior for use as supplemental fixation. Haskell et al (2) performed a retrospective chart review on 101 subtalar joint arthrodeses using a single lag screw inserted from posterior to anterior. They demonstrated a 98% fusion rate at an average of 12.3 weeks, demonstrating this technique to be a reliable form of fixation. The distal tip of this screw should be within the talar body, with attention made to avoid the ankle joint. The benefit of application of the posterior to anterior screw with this technique is the use of the drill guide with the guide wire from the anterior to posterior screw. If a single posterior to anterior screw is used, the guide wire must be driven through the calcaneus approximately 50 mm before engaging the talus. This substantial length means that any minute error in guide wire placement can be magnified leading to misalignment or poor fixation construct (4). The technique described previously aids in proper screw placement while minimizing the risk of error. Although both orientations of screw placement have been shown to lead to fusion individually, the use of both screws may aid in fusion in suboptimal conditions in difficult patient populations. The addition of a second point of fixation may also create greater rotational stability across the arthrodesis site (4). Certain factors have been shown to delay fusion or increase the nonunion rates of rearfoot fusion. Haskell et al (2) demonstrated a delay in subtalar fusion with ipsilateral ankle fusion performed at the same time, whereas Easley et al (8) showed a nonunion rate of 33% for subtalar joint fusion with prior ankle fusion. Possible explanations for these findings are increased motion and stress at joints owing to prior fusions, as well as soft tissue damage from extensive and repeated exposure. Other causes of delayed or nonunion of rearfoot fusions include diabetes, smoking, osteopenic bone, avascular necrosis of the talus, and
309
infection (14). Supplemental fixation with 2 forms of fixation may aid in enhanced stability providing the surgeon with better outcomes. In conclusion, isolated subtalar joint fusion is generally known to be effective with high subjective satisfaction for patients with instability, pain, or deformity who have failed nonoperative treatment. The technique described herein may also be used in conjunction with triple arthrodesis. The simplistic design of this technique may aid surgeons operating alone when they perform this potentially difficult procedure. The technique that we have described is a systematic, reliable, reproducible way to perform a subtalar joint fusion with excellent anatomical placement of screw fixation.
References 1. Diezi C, Favre P, Vienne P. Primary isolated subtalar arthrodesis: outcome after 2 to 5 years follow up. Foot Ankle Int 29:1195–1202, 2008. 2. Haskell A, Pfeiff C, Mann R. Subtalar joint arthrodesis using a single lag screw. Foot Ankle Int 25:774–777, 2004. 3. Wilson P. Treatment of the fractures of os calcis by arthrodesing of the subtalar joint: a report of 26 cases. JAMA 89:1676–1683, 1927. 4. McGlamry MC, Robitaille MF. Analysis of screw pullout strength: a function of screw orientation in subtalar joint arthrodesis. J Foot Ankle Surg 43:277–284, 2004. 5. Gable SJ, Bohay DR, Manoli A 2nd. Aiming guide for accurate placement of subtalar joint screws. Foot Ankle Int 16:238–239, 1995. 6. Bori G, Soriano A, Garcia S, Mallofre C, Riba J, Mensa J. Usefulness of histological analysis for predicting the presence of microorganisms at the time of reimplantation after hip resection arthroplasty for the treatment of infection. J Bone Joint Surg Am 89-A:1232–1237, 2007. 7. Dennyson WG, Fulford GE. Subtalar arthrodesis by cancellous grafts and metallic internal fixation. J Bone Joint Surg Br 58-B:507–510, 1976. 8. Easley ME, Trnka HJ, Schon LC, Myerson MS. Isolated subtalar arthrodesis. J Bone Joint Surg Am 82-A:613–624, 2000. 9. Gosch C, Verrette R, Lindsey DP, Beaupre GS, Lehnert B. Comparison of initial compression force across the subtalar joint by two different screw fixation techniques. J Foot Ankle Surg 45:168–173, 2006. 10. Mann RA, Beaman DN, Horton GA. Isolated subtalar arthrodesis. Foot Ankle Int 19:511–519, 1998. 11. Thomas FB. Arthrodesis of the subtalar joint. J Bone Joint Surg Br 49-B:93–97, 1967. 12. Finlay JB, Harada I, Bourne RB, Rorabeck CH, Hardie R, Scott MA. Analysis of the pull-out strength of screws and pegs used to secure tibial components following total knee arthroplasty. Clin Orthop Relat Res 247:220–231, 1989. 13. Chapman JR, Harrington RM, Lee KM, Anderson PA, Tencer AF, Kowalski D. Factors affecting the pullout strength of cancellous bone screws. J Biomech Eng 118:391– 398, 1996. 14. Chuckpaiwong B, Easley ME, Glisson RR. Screw placement in subtalar arthrodesis: a biomechanical study. Foot Ankle Int 30:133–141, 2009.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Technique Tip: Subtalar Joint Fusion Using a Parallel Guide and Double Screw Fixation Rick L. Scanlan, DPM 1, Patrick R. Burns, DPM 2, Brandon E. Crim, DPM 3 1
Private Practice, Ankle and Foot Centers of Pittsburgh, Attending, Podiatric Medicine and Surgery Residency Program, University of Pittsburgh Medical Center, Pittsburgh, PA Residency Director, Podiatric Medicine and Surgery Residency Program, University of Pittsburgh Medical Center, Department of Orthopedics, Pittsburgh, PA 3 Resident, University of Pittsburgh Medical Center, Pittsburgh, PA 2
a r t i c l e i n f o
a b s t r a c t
Keywords: arthrodesis calcaneus interfragmental compression lag screw osteosynthesis talus
A wide range of techniques has been described to achieve subtalar (talocalcaneal) arthrodesis using interfragmental screw fixation. In this technical report, we describe a method that enables us to accurately position 2 screws across the subtalar joint in order to achieve arthrodesis between the talus and calcaneus. Careful attention to the tips described in this report should minimize the risk of aberrant placement of the screws while expediting the process of osteosynthesis. Ó 2010 by the American College of Foot and Ankle Surgeons. All rights reserved.
Subtalar joint arthrodesis is a surgical option for patients with pain, instability, or deformity who have failed nonoperative treatment. The goal of any subtalar joint fusion is the elimination of motion of the subtalar joint complex, thus eliminating pain for patients, allowing them to return to their past level of activity (1). Isolated subtalar arthrodesis has been shown to result in good to excellent outcomes with high patient satisfaction, with reported fusion rates with the use of screw fixation often exceeding 90% (1, 2). Arthrodesis can be used in patients with prior trauma, such as calcaneal or talar fracture, resulting in degenerative joint changes (1). Subtalar joint fusion has also been described in patients with primary subtalar degeneration, inflammatory arthropathies, rearfoot coalitions, neuromuscular dysfunction, and following infectious degenerative changes. Subtalar joint arthrodesis can also be useful in residual congenital hindfoot deformities, as well as rearfoot deformities such as rigid pes planovalgus and cavus foot. Arthrodesis also restores hindfoot alignment and improves function (2). Wilson (3) was the first to describe isolated subtalar joint arthrodesis in the English literature, and used the fusion to treat patients with intra-articular damage following calcaneal fracture. Since then, many forms of fixation have been described for fusion of the subtalar joint. Internal screw fixation has become an established form of fixation (4). Accurate placement of screw fixation is imperative because improper
Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Brandon E. Crim, DPM, Resident, University of Pittsburgh Medical Center, UPMC Mercy, c/o Debra Bodner, 1400 Locust Street, Pittsburgh, PA 15219. E-mail address: [email protected] (B.E. Crim).
positioning and application of fixation can lead to poor outcomes affecting the function of the entire lower extremity (5). In this report, the authors share a systematic, reliable, reproducible way to perform a subtalar joint fusion with excellent anatomical placement of screw fixation. Surgical Technique The patient is positioned supine on the operating table with bump placement under the ipsilateral hip for needed internal rotation to properly visualize the lateral aspect of the foot. If the surgeon prefers, a tourniquet can be applied to the ipsilateral thigh for hemostasis. The subtalar joint is approached laterally with an incision, which extends from the tip of the fibula to the calcaneocuboid joint. The distal portion of the incision can be extended to the base of the fourth metatarsal if a triple arthrodesis is being performed (Figure 1). The incision is deepened through the subcutaneous tissue with atraumatic technique, with particular care to avoid the communicating branch of the sural nerve. The extensor digitorum brevis muscle belly is reflected dorsally or distally, and the fatty plug (Hoke’s tonsil) is removed from the sinus tarsi. The subtalar joint is then prepared for fusion using the preferred technique of the surgeon; our preferred technique is curettage with subchondral drilling. It is imperative that all cartilage is removed and healthy bleeding bone is visualized, which is optimal for fusion. A lamina spreader may be used to visualize the medial portion of the subtalar joint for joint preparation. If a talocalcaneal coalition is present, it should be resected in order to prepare the remainder of the joint. Following joint preparation, rearfoot alignment should be inspected and any deformity correction such as heel varus should be performed through osteotomies or bone block
1067-2516/$ – see front matter Ó 2010 by the American College of Foot and Ankle Surgeons. All rights reserved. doi:10.1053/j.jfas.2010.02.017
306
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
Fig. 1. Incision placement for lateral access to the subtalar joint. The incision extends from the tip of the fibula to the calcaneocuboid joint. The incision can be lengthened distally to the base of the fourth metatarsal for a triple arthrodesis.
placement. Bone graft, bone morphogenic protein, and/or plateletrich plasma may also be added to the prepared joint to aid timely fusion. The dorsal surface of the talar neck is then approached using an approximately 2-cm midline incision (Figure 2). This location can be visualized under fluoroscopy using a metal object such as a Freer elevator to locate the proper position. The interval for the incision is located between the tibialis anterior and the extensor hallucis longus tendons. This interval is safe relative to position of the dorsalis pedis artery and deep peroneal nerve, and it is imperative to locate the proper interval between the tibialis anterior and extensor hallucis longus to avoid any neurovascular damage. The skin incision is made, and blunt dissection is then carried down to the neck of the talus. A small portion of the periosteum is removed using a Key elevator in the area of planned screw placement. A guide pin is then inserted from the anterior incision through the neck of the talus, crossing the subtalar joint, into the calcaneus (Figures 3 and 4). Before crossing the posterior facet of the subtalar joint, the foot should be placed in the appropriate position for subtalar fusion. The proper frontal plane positioning of the rearfoot is typically 5 of valgus, which allows motion at the midtarsal joint. It is important to remember that the subtalar joint influences the midtarsal joint, and if placed in varus, the midtarsal joint will remain locked at all times during the gait cycle. Attention must also be paid to obtaining the desired sagittal and transverse plane alignments, which vary depending on the individual patient’s needs and anatomy. Next, proper placement of the guide pin should be verified in multiple planes before application of screw fixation. The lateral image will show proper placement in the sagittal plane, and should show the guide wire clearly crossing the talocalcaneal joint (Figure 4). An anteroposterior (AP) ankle view should show the guide wire properly placed within the talus, whereas a calcaneal axial view should show the wire within the calcaneal body. Although the lateral fluoroscopic image is an advantageous view, the other images can help prevent placement of hardware within problematic areas such as the ankle gutters and tarsal tunnel. Once correct guide pin placement is noted under fluoroscopy, a 6.5-mm partially threaded long thread pattern screw is inserted (Figure 5). This screw is inserted using standard osteosynthesis lag technique, with aggressive countersinking to avoid anterior ankle impingement. Headless screws are also an option so as
Fig. 2. Incision placement for access to the talar neck. Proper location can be verified with a lateral fluoroscopic image before incision. The interval for the incision is between the tibialis anterior and extensor hallucis longus tendons. This interval is a ‘‘safe zone’’ away from the anterior neurovascular bundle, but the soft tissues must be retracted with care.
to prevent anterior ankle impingement. Proper screw placement should include the neck of the talus to the body of the calcaneus, with care taken to avoid violation of the inferior cortex of the calcaneus. Once proper screw placement is noted in all planes, the anterior to posterior guide pin is then advanced until it exits the heel (Figure 6). Using the guide wire, which exits the posterior heel, a parallel drill guide is used for placement of the posterior to anterior screw (Figure 7). Proper screw placement for the posterior to anterior screw should include avoidance of the plantar aspect of the calcaneus, as well as the posterior surface of the calcaneus, which can result in screw prominence against the last of the shoe. The guide wire should cross the posterior facet of the subtalar joint and enter the talar body (Figure 8). A 6.5-mm partially threaded short thread pattern screw should be inserted using standard osteosynthesis lag technique (Figure 9, 10). Aggressive countersinking should be used to prevent screw prominence. With either the anterior to posterior screw, or the posterior to anterior screw, if screw threads are crossing the posterior facet, the surgeon can overdrill the proximal segment so as to convert screw placement to lag by technique. Both guide pins are then removed, and proper fixation and alignment should be noted by direct visualization and image intensification fluoroscopy. The area should be flushed with sterile saline, after which proper layer closure is performed. The lower extremity can then be placed in a posterior splint and managed with avoidance of weight bearing on the operated extremity.
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
307
Fig. 3. Application of guide pin for the anterior to posterior screw through the anterior approach. Before crossing the subtalar joint, the rearfoot should be placed in the proper position for fusion.
Fig. 5. Application of 6.5-mm long thread cannulated screw using standard osteosynthesis technique.
Fig. 4. Fluoroscopic confirmation viewed on lateral projection of proper guide pin placement before application of cannulated screw. An anteroposterior ankle should also be taken before application of the screw to ensure proper placement. The screw should enter the talar neck, and extend into the calcaneal body.
Fig. 6. Following the application of the anterior to posterior screw and confirmation of proper placement with fluoroscopy, the guide pin is advanced through the posterior heel. The guide wire will then be used for the application of the posterior to anterior screw using a drill guide.
308
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
Fig. 7. Application of guide wire for the posterior to anterior screw using the parallel drill guide.
Fig. 9. Application of posterior to anterior screw. A 6.5-mm short thread cannulated screw is being inserted for supplemental fixation.
If a revisional arthrodesis is being performed, all hardware must be removed to access the joint. The presence of infection is a direct contraindication to the application of internal fixation, and can be identified using frozen section microscopy, wherein greater than 5 polymorphonuclear leukocytes per high-power field (400) suggests the presence of infection (6). Once infection has been ruled out, the subtalar joint should be prepared to bleeding, healthy tissue, and bone graft may be warranted if the previous resection resulted in significant bone loss. Application of fixation can then follow the technique described above, and the surgeon may consider adjunctive therapy such as bone stimulation.
compression limits motion, which aids bone union. Screws have become a popular form of fixation for subtalar arthrodesis (4). There is no true consensus in the literature as to the need for 1 or 2 screws, and the orientation of these screws also remains a question of the surgeon’s preference. There are benefits, most notably interfragmental compression, associated with either orientation of screw fixation, from anterior to posterior (talus to calcaneus) or posterior to anterior (calcaneus to talus). The benefits of the anterior to posterior screw include ease of placement, and the ability to use the long thread pattern of a partially threaded screw using lag by design technique. Using the long thread pattern enables the screw’s threads to contact more cancellous bone. Finlay et al (12) demonstrated the importance of maximizing contact between the screw and the bone so as to enhance the pullout strength. In a study by McGlamry and Robitaille (4), the anterior to posterior screw showed a higher torque of insertion and pullout strength/failure load when using a cannulated system when compared with a posterior to anterior placed screw. Torque is important because screws are designed to convert torque to
Discussion Many forms of fixation for subtalar joint arthrodesis have been described, including Kirschner wires, staples, screws, and external fixation (2, 4, 7–11). Although studies have been unable to show how much compression is needed for joint fusion, it is understood that
Fig. 8. Confirmation of proper guide wire placement for posterior to anterior screw. The screw should extend from the posterior calcaneus to the talar body.
Fig. 10. Fluoroscopic confirmation of proper screw placement. The screw will be advanced to prevent posterior screw head prominence.
R.L. Scanlan et al. / The Journal of Foot & Ankle Surgery 49 (2010) 305–309
compression. Greater torque of insertion of the anterior to posterior screw leads to greater compression between joint surfaces leading to greater stability. Another advantage of the anterior to posterior screw is the bone stock at the entrance point of the screw has been found to be critical to stable internal fixation; Chapman et al (13) showed that the best screw placement is where the entrance cortex is thickest. For subtalar arthrodesis, this corresponds to the thick dorsal cortex of the calcaneus. Because of the small area of the talar neck, placement of supplemental fixation from anterior to posterior can be difficult. Using the technique described, placement of a short thread pattern partially threaded cannulated screw can be inserted from posterior to anterior for use as supplemental fixation. Haskell et al (2) performed a retrospective chart review on 101 subtalar joint arthrodeses using a single lag screw inserted from posterior to anterior. They demonstrated a 98% fusion rate at an average of 12.3 weeks, demonstrating this technique to be a reliable form of fixation. The distal tip of this screw should be within the talar body, with attention made to avoid the ankle joint. The benefit of application of the posterior to anterior screw with this technique is the use of the drill guide with the guide wire from the anterior to posterior screw. If a single posterior to anterior screw is used, the guide wire must be driven through the calcaneus approximately 50 mm before engaging the talus. This substantial length means that any minute error in guide wire placement can be magnified leading to misalignment or poor fixation construct (4). The technique described previously aids in proper screw placement while minimizing the risk of error. Although both orientations of screw placement have been shown to lead to fusion individually, the use of both screws may aid in fusion in suboptimal conditions in difficult patient populations. The addition of a second point of fixation may also create greater rotational stability across the arthrodesis site (4). Certain factors have been shown to delay fusion or increase the nonunion rates of rearfoot fusion. Haskell et al (2) demonstrated a delay in subtalar fusion with ipsilateral ankle fusion performed at the same time, whereas Easley et al (8) showed a nonunion rate of 33% for subtalar joint fusion with prior ankle fusion. Possible explanations for these findings are increased motion and stress at joints owing to prior fusions, as well as soft tissue damage from extensive and repeated exposure. Other causes of delayed or nonunion of rearfoot fusions include diabetes, smoking, osteopenic bone, avascular necrosis of the talus, and
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infection (14). Supplemental fixation with 2 forms of fixation may aid in enhanced stability providing the surgeon with better outcomes. In conclusion, isolated subtalar joint fusion is generally known to be effective with high subjective satisfaction for patients with instability, pain, or deformity who have failed nonoperative treatment. The technique described herein may also be used in conjunction with triple arthrodesis. The simplistic design of this technique may aid surgeons operating alone when they perform this potentially difficult procedure. The technique that we have described is a systematic, reliable, reproducible way to perform a subtalar joint fusion with excellent anatomical placement of screw fixation.
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