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Minimally invasive hip replacement: rationale, applied anatomy, and instrumentation
Orthop Clin N Am 35 (2004) 107 – 118
Minimally invasive hip replacement: rationale, applied anatomy, and instrumentation Jonathan R. Howell, FRCS(Tr&Orth), Donald S. Garbuz, MD, MHSc, FRCS(C)*, Clive P. Duncan, MD, MSc, FRCS(C) University of British Columbia, Room 3114, 910 West 10th Avenue, Vancouver, British Columbia, V5Z 4E3, Canada
The last three decades have seen the development of minimally invasive surgery (MIS) techniques in a range of specialties, including abdominal surgery, thoracic surgery, and neurosurgery. Orthopedics has been no exception, with MIS techniques used to perform operations on several joints, such as the knee, shoulder, wrist, ankle, and hip. In the hip, arthroscopic techniques have been used for the treatment of labral tears [1 – 3], instability [4,5], infection [6,7], and the removal of loose and foreign bodies [8 – 10]. The arthroscope also has been used to assess polyethylene wear of total hip replacements [11] and as an adjuvant tool for visualization of the femoral canal during revision hip arthroplasty [12]. In recent years advances in operative techniques and instrumentation have allowed surgeons to perform total hip arthroplasty (THA) through incisions much smaller than those used previously. The definition of what constitutes MIS hip arthroplasty has yet to be finalized, but at present, the term MIS THA may be applied to any hip replacement procedure in which the length of the wound and the surgical access are deliberately modified in an attempt to reduce the tissue trauma associated with hip replacement, with most investigators reporting wounds of 10 cm length or less [13 – 20]. The minimum length of the inci-
Jonathan R. Howell was supported by a grant from The John Charnley Trust. * Corresponding author. E-mail address: [email protected] (D.S. Garbuz).
sion that can be used without skin stretch is determined by the diameter of the acetabular component that is to be used. For the cup to be inserted without touching or stretching the skin edges, the length of the incision must be equal to at least half the length of the cup circumference, because each skin flap must pass around one half of the component. Based on an acetabular component diameter of 56 mm, Goldstein [17] has estimated that a 4-inch incision is required to avoid contact between the cup and the subcutaneous fat. Several techniques of MIS hip arthroplasty have been described [16 – 23], and the authors have found it useful to divide the various MIS approaches into two main categories: the minimal incision approaches and the two-incision approach. The minimal incision approaches are modifications of the standard posterior, anterolateral, and anterior approaches that are used commonly for hip arthroplasty and are performed through wounds 7 – 10 cm in length. The two-incision approach constitutes a new approach for hip replacement, using intermuscular planes to gain access to the hip joint and minimizing the dissection of muscles and tendons. Whichever technique is used, the reduced length of incision and the reduced dissection mean that exposure may be difficult using standard instruments. The development of MIS hip arthroplasty therefore has been accompanied by the development of specialized instruments designed to facilitate exposure and bony preparation. In this article the authors review the rationale, surgical anatomy, and instrumentation of MIS THA.
0030-5898/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/S0030-5898(03)00112-3
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Rationale for minimally invasive hip replacement Advantages for patients MIS techniques have the potential to benefit patients in several ways, as a consequence of the reduced dissection associated with the surgical access. In the medium to long term, hip arthroplasty using conventional surgical techniques has been shown to produce improvements in pain, function, mood, general health, and quality of life [24,25], but the postoperative period remains one characterized by pain and reduced function [26]. Through a reduction in the degree of tissue disruption, MIS hip arthroplasty has the potential to reduce perioperative blood loss and pain in the immediate postoperative period and to preserve muscle function, thereby leading to an earlier recovery of normal activities [23,27] and an earlier discharge from the hospital. Several studies [14,17,20,22,23] have found a reduction in the estimated blood loss following MIS THA, although this is not a universal finding [15], and the reliability of estimated blood loss as a measurement tool is open to question. Indeed, Goldstein [17] found that although estimated blood loss was significantly less in patients undergoing MIS THA, the postoperative hemoglobin tended to be higher in their control group ( P = 0.05) and there was no difference in the transfusion requirements between the two groups. DiGioia et al [23] selected 33 mini-incision patients from their cohort of 121 and compared these to matched control subjects. They found that using a postoperative hematocrit measurement of 0.28 as the indication for transfusion, the mini-incision group of patients received a mean 0.7 units of blood, compared with 1.1 units in the control group (P < 0.05). Similarly, Wenz et al [22] found that MIS patients required a mean of 0.3 units of blood, compared with 0.6 units for control subjects who had their operation performed through an anterolateral approach ( P = 0.006). Although both of these studies demonstrated statistically significant results, however, the clinical significance of these differences is questionable. There is little in the literature to support the contention that MIS THA is associated with less pain. Chimento et al [14] found no difference in narcotic requirements in their randomized controlled trial. Swanson and Hanna [20] defined ‘‘problem pain’’ as deviation from their standard postoperative pain management protocol. They found that no MIS patients suffered from ‘‘problem pain’’ compared with 12% of the control patients ( P < 0.001), but the use of historical control subjects in this study has the
potential to introduce bias into their results. Dorr [18] has described in detail the pain and analgesia requirements of 90 patients undergoing MIS THA, but without control subjects the results are difficult to interpret. The recovery of function has been studied more extensively, with many positive results. Wenz et al [22] found that their MIS patients ambulated significantly sooner in the postoperative period ( P = 0.02), but the mean length of stay was similar in both groups. That study compared MIS posterior approach with a standard length incision lateral approach, and the recovery of ambulation may owe as much to the approach as to the incision. Chimento et al [14] found that significantly fewer of their MIS patients limped at 6 weeks ( P < 0.04), but there was no difference in the length of hospital stay, and DiGioia et al [23] reported similar findings, with patients showing significantly higher Harris Hip Scores 3 months ( P = 0.45) and 6 months ( P = 0.17) after mini-incision THA. They found that there was no difference in the mean length of hospital stay between mini-incision and standard incision patients; this also was confirmed by Wright et al [15]. Swanson and Hanna [20] found that MIS patients made a faster return to full activity ( P < 0.001), and Berger [16], Dorr [18], and Sherry [28] have all reported favorable recovery of postoperative function with short lengths of stay, but in each of these last three studies there was no control group for comparison. DiGioia et al [23] found no differences in the functional outcome in their two groups 1 year after surgery. There are cosmetic advantages to the use of the smaller incisions of the MIS technique and this may be a factor that propels MIS hip arthroplasty into widespread orthopaedic practice. Three studies [15, 17,18] have reported favorable patient attitudes toward the scars that result from MIS THA, and indeed Wright et al [15] concluded that ‘‘this investigation confirms no dramatic clinical benefit of an abridged surgical approach other than cosmetic appeal to the patient.’’ Advantages for health care providers MIS holds several potential advantages for institutions and individuals providing orthopaedic care. In other fields of surgery the introduction of MIS techniques has radically reduced recovery times and lengths of hospital stay, and as surgeons face pressures to reduce length of stay and hospital costs [29], MIS hip arthroplasty may assist toward these goals. The influence of length of hospital stay on total cost is, however, controversial, and the orthopaedic
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literature is deficient in well designed economic evaluations of different surgical strategies in hip arthroplasty [30,31]. Healy et al [32] have shown that almost 80% of total hospital costs associated with the provision of THA are generated within the first 48 hours of admission; in the operating room, recovery room, pharmacy, and in postoperative nursing costs. In their study they found that the cost of the first hospital day was the most expensive at $6,343, which constituted 68.25% of the total costs, and these costs reduced dramatically to $188 by the sixth day of hospital admission. To have a major effect on the total costs of providing a hip arthroplasty service, MIS techniques therefore will need to reduce hospital length of stay to less than 48 hours, and even then many of the costs remain fixed. There are reports of day care hip arthroplasty [16,27] using MIS techniques, but it is unclear at this stage whether this will become a reality for most patients. Indeed, efforts to achieve this may increase referral rates to rehabilitation units, particularly for elderly patients, patients who live alone, and those with comorbid conditions [33]. The economic benefits of MIS hip arthroplasty therefore remain unproven at the present time. Healy [34] found that the introduction of a clinical pathway and a hip implant standardization program have in themselves led to a substantial reduction in length of stay and hospital costs without adversely affecting outcomes. The orthopaedic community must study carefully the effect that the introduction of MIS techniques has on the health economics of THA over and above the effects of introducing well designed care pathways that facilitate early discharge from hospital. A more detailed economic analysis is presented in a separate article in this issue. Potential disadvantages of minimally invasive hip replacement
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found that surgical times using MIS techniques were slightly shorter than in a cohort of control patients (P < 0.02), but the MIS patients in this study weighed less than control subjects (P < 0.03). Swanson and Hanna [20] showed that MIS surgery was faster (P < 0.0001), but in this study they compared cementless THA through an MIS approach with historical control subjects who had hybrid THAs. Wenz et al [22] also have shown reduced surgical times with the MIS posterior approach. The MIS patients were a single-surgeon series, however, whereas the control subjects were not, and the mean surgical time for primary THA in the control group was 164 minutes. Although the authors have not experienced problems, the use of unfamiliar approaches and instruments may lead to an increase in early complications, such as neurovascular injuries, infections, thromboembolism, and component malposition. This last complication then may lead to longer-term complications, such as instability, osteolysis, and loosening. Several studies [14,15,17,20,22] have failed to show any difference in the rates of these complications, and at present these concerns remain theoretic. It is the authors’ opinion that, although this surgical technique is in its infancy, it should be performed only by surgeons who are experienced in hip replacement through open techniques, and it is essential that the rates of complications be monitored carefully.
Surgical anatomy and instrumentation of minimally invasive surgery hip arthroplasty Full descriptions of the techniques used for the various approaches are provided in other articles in this issue, and so the authors shall describe here only anatomic issues as they pertain to each approach. Minimal posterior approach
The introduction of a new surgical technique always has the potential for disadvantages and advantages, and MIS hip arthroplasty is no exception. In the authors’ experience of using the two-incision technique there is an initial learning curve during which the surgical duration is longer than normal for primary total hip replacement, but with experience the operating time can be reduced. This also has been the experience of others [16]. Several studies have addressed the issue of operative time using the minimal posterior approach. Chimento et al [14] found no difference in the mean operative time between MIS patients and control subjects in their prospective randomized trial, and this result is supported by the findings of Goldstein et al [17]. Wright et al [15]
The position of the skin incision for the minimal posterior approach differs slightly between investigators. The authors use a 7 – 10-cm incision placed along the posterior aspect of the greater trochanter with 70% of the incision placed distal to the tip of the greater trochanter and 30% proximal to it (Fig. 1A), similar to the approach described by Chimento and Sculco [21]. Dorr [18] advocates the use of a 5 – 10-cm straight incision along the posterior border of the greater trochanter from a point proximally level with the tip of the greater trochanter to a point distally that is level with the vastus tubercle of the femur. Goldstein [17] draws his standard incision on the skin and then uses this to guide the incision for
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Fig. 1. Minimal incision posterolateral approach to the left hip. (A) Skin markings showing greater trochanter and the planned skin incision. (Courtesy of Zimmer Inc., Warsaw, IN; with permission.) (B) Diagram showing position of retractors for acetabular exposure (C) Skin incision for the posterior approach described by Sherry [13,28]. (Courtesy of Dr. E. Sherry, Sydney, New South Wale, Australia.) (D) The neck osteotomy is made in situ using a cutting block. (Courtesy of Dr. E. Sherry, Sydney, New South Wale, Australia.) (E) The ‘‘lollipop’’ device is used to insert the acetabular component. (Courtesy of Dr. E. Sherry, Sydney, New South Wale, Australia.)
the minimal approach. A 4-inch incision is planned 2 – 3 cm posterior to the apex of the standard incision between the two endpoints of the longer incision. This new incision also is moved 2 cm posterior and superior toward the posterior – inferior spine of the
pelvis. Swanson [20] has described a 10-cm incision, the starting point of which is located by measuring 4 cm distal to the tip of the greater trochanter along the line of the femur, and then measuring 4 cm posterior to the femur. From this point the incision
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is made in a proximal direction, angled posteriorly at 20° to the line of the femur. DiGioia [23] plans his incision with the affected leg placed in 70° – 80° of flexion. An 8 – 12-cm incision is made in line with the shaft of the femur, with two thirds of the incision lying proximal to the tip of the greater trochanter and one third distal to it. The common principle underlying all these incisions is the creation of a mobile window that can be moved to different positions during different stages of the operation. After the incision, the anatomy of the approach is similar to a standard posterior approach, but the small incision means that great care should be taken to protect soft tissues when using power instruments. Adequate acetabular exposure requires precise placement of retractors (Fig. 1B), the first of which is placed over the anterior column and retracts the femoral metaphysis anteriorly; to mobilize the femur sufficiently it may be necessary to incise the inferior capsule down to the transverse acetabular ligament. A second retractor is placed over the posterior lip of the acetabulum, and with care to avoid injury to the sciatic nerve, retracts the posterior tissues. If necessary a third retractor may be placed underneath the cotyloid notch. This retractor should be removed at the time of cup insertion. To expose the femur, the acetabular retractors are removed and then the dependent leg is moved into 30° – 45° of flexion, maximum adduction, and 90° of internal rotation. A femoral elevator is placed under the femoral neck, thus delivering the proximal femur into the wound. Placement of a retractor along the medial aspect of the calcar further improves access for preparation of the femoral canal. A gluteus medius retractor is also potentially helpful in allowing a properly lateralized entry point in the proximal femur. Sherry described the use of an alternative posterior approach for MIS THA that avoids dislocation of the hip joint before neck osteotomy and that may, therefore, reduce soft tissue disruption [13,28]. A 5-cm incision is made starting one fingerbreadth behind the prominence of the greater trochanter and curved backward at 45° to the long axis of the femur (Fig. 1C). The approach is similar to that used by other investigators, except that the quadratus femoris is left intact and a posterior capsulectomy is performed to expose the femoral neck. A cutting block then is used to guide the osteotomy, which is made with the hip in situ followed by removal of the head (Fig. 1D). The position of the incision makes access to the proximal femur easy, but exposure of the acetabulum may be more limited. This is overcome through the use of specialized angled reamers and a
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‘‘lollipop’’ positioning device for insertion of the acetabular component (Fig. 1E). Minimal anterolateral approach: technique and applied anatomy The minimal anterolateral approach is a modification of the anterolateral approach described by Hardinge et al in 1982 [35]. The surgeon first marks the tip and then the anteroposterior midline of the greater trochanter. A point is then measured along this midline, 2 cm distal to the tip of the trochanter, and this point becomes the midpoint of the incision. A 3-inch incision is then marked, extending 1.5 inches either side of the midpoint, at an angle of 30° – 45° with the long access of the femur (Fig. 2A). The fascia lata then is divided in the line of its fibers and not in line with the initial incision. The remaining anatomy is similar to the standard anterolateral approach, but again, acetabular exposure depends on accurate placement of retractors. The first retractor is placed over the posterior – inferior border of the acetabulum and retracts the femur posteriorly. Placement of this retractor is assisted by flexion, adduction, and external rotation of the hip. A second retractor is placed over the anterior superior aspect of the acetabulum and retracts the gluteus medius and minimus tendons, and if necessary a third retractor is placed over the anterior inferior acetabular margin, which retracts the psoas tendon and completes the acetabular exposure (Fig. 2B). To expose the femur, the acetabular retractors are removed and the hip is flexed adducted and externally rotated. A femoral elevator is placed under the femoral neck to deliver the femur into the wound, and a second retractor is placed in the piriformis fossa to retract the gluteus medius tendon. Finally, a retractor is placed along the medial calcar to retract the vastus lateralis, resulting in clear exposure of the femoral canal (Fig. 2C). Minimal anterior approach The MIS anterior approach is a modification of the Smith-Peterson approach that uses an intermuscular, internervous plane to gain access to the anterior aspect of the hip joint. Keggi [19,36] has described making a 5 – 8-cm curved incision, with its convexity placed laterally, from a point just distal to the anterior superior iliac spine extending to the anterior border of the greater trochanter. The deep dissection is through a plane between tensor fascia lata (superior gluteal nerve) and the sartorius (femoral nerve), and then deep to this, the dissection is extended between the
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Fig. 2. Minimal incision anterolateral approach to the right hip. (A) Anatomic landmarks for the skin incision. (Courtesy of Zimmer Inc., Warsaw, IN; with permission.) (B) Intraoperative photograph showing the acetabular exposure that can be achieved using the minimal incision anterolateral approach. (C) Intraoperative photograph showing femoral exposure.
rectus femoris (femoral nerve) medially and gluteus medius (superior gluteal nerve) laterally, which exposes the anterior aspect of the hip joint capsule. The structures at risk from this approach are the lateral cutaneous nerve of the thigh and the lateral circumflex femoral artery [37]. To avoid injury to the lateral cutaneous nerve of the thigh, Keggi recommends dissecting through the anterior border of tensor fascia lata and retracting the anterior border medially. The approach affords good exposure of the acetabulum, and in most patients reaming may be performed through this incision using a straight reamer. In larger patients access is difficult, however, and Keggi describes the use of a separate stab incision through which the surgeon may pass the reamer handle and later the shell impactor in a retrograde direction before use of the instrument. In the past the anterior approach has been considered to give inadequate exposure of the femoral canal [37]. Keggi states that this may be overcome by extreme external rotation of the femur and placement of a bone hook around the femur at the level of the
lesser trochanter, which is then used to deliver the femur into the wound. Placing a small sandbag centrally under the sacrum before the start of the operation helps with the leg extension that is required for this maneuver, but the surgeon must be careful that this does not alter the position of the acetabular component when that is inserted. In some cases this maneuver is not sufficient to expose the femoral canal, in which case the exposure can be improved by dividing the posterior capsule and dissection of the short external rotators from the posterior aspect of the proximal femur [19], although such dissection undertaken without repair of the posterior tissues seems to contradict the principles of tissue preservation inherent in the MIS approach. Two-incision minimally invasive approach The two-incision approach was described by Berger et al following on the work of Mears [16], who initially developed this technique. The principle of the approach is two incisions, one for the acetab-
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ulum and one for the femur, avoiding the division of muscle or tendons, thereby aiming to achieve a faster recovery of normal function. To guide the incision, the anterior – superior iliac spine and the tip of the greater trochanter are marked on the sterile drapes. The femoral neck lies approxi-
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mately three fingerbreadths distal to the line that connects these two marks, and its position is confirmed using fluoroscopy. The 2-inch incision is marked along this line extending on the fluoroscopy image from the head – neck junction to the intertrochanteric line (Fig. 3A). After the incision, the dis-
Fig. 3. Acetabular exposure using the two-incision minimally invasive approach. (A) The femoral neck lies three fingerbreadths distal to a line joining the anterior – superior iliac spine and the tip of the greater trochanter. The anterior skin incision is marked using fluoroscopy to guide the position. (B) The deep fascia is incised to reveal the underlying tensor fascia lata. (C) Tensor fascia lata is retracted to reveal rectus femoris. (D) Artery forceps have been placed under branches of the lateral femoral circumflex artery, which must be cauterized. (E) The neck osteotomy is made in situ and a ‘‘hockey puck’’ segment of the head and neck junction is removed.
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section is similar to the minimal incision anterior approach (Figs. 3B – D). The hip joint capsule is exposed by placing retractors over the superolateral aspect of the femoral neck, inferomedial to the neck and over the front of the capsule heading medially to engage the anterior column. The assistant moves the hip joint to confirm the joint line and then an H-shaped capsulotomy is made with elevation of the flaps for later repair. The lip of the acetabulum is exposed and the retractors are replaced inside the capsule and around the neck of the femur to expose the head – neck junction of the femur. The hip usually cannot be dislocated at this stage and instead the neck osteotomy is made in situ. This is best done as two osteotomies, the first of which is made at the head – neck junction. The second osteotomy is made further down the neck and the intervening ‘‘hockey puck’’ section of the neck is removed using a Schanz pin (Fig. 3E). This allows removal of the remaining femoral head from the socket, and the acetabulum is exposed by placing one retractor over the anterior column, one over the posterior lip of the acetabulum, and a third placed anteroinferior to the acetabulum. To access the femur, the surgeon passes a piriformis fossa guide or an index finger from the back of the proximal femur around the posterior aspect of the gluteus medius pointing proximally and posteriorly
into the buttock. A 2-cm transverse incision is marked on the skin over the guide or the surgeon’s finger if this is used instead (Fig. 4A). The surgeon’s second index finger then passes through this incision to find the piriformis fossa and a taper pin awl is guided to the piriformis fossa and starts the entry point in the femoral canal (Fig. 4B). Once the initial entry point is made, the femur is prepared using reamers and rasps inserted through the posterior incision, using fluoroscopy to guide depth of insertion of the instruments and to confirm their correct alignment. The ideal location of this incision and the subsequent plane through the soft tissues is between the posterior border of the gluteus medius and the piriformis, down to their femoral attachments. Instrumentation for minimally invasive hip replacement Performing MIS hip replacement is challenging, but the difficulties of the operation can be reduced if instruments developed for the technique are used. Achieving the correct exposure is one of the major challenges, for which several companies have developed specialized retractors. These retractors have long handles, angled at approximately 90° to the blade, so that the assistant’s hands are kept at a distance from
Fig. 4. Femoral exposure using the two-incision minimally invasive approach. (A) Marking the incision for the femoral approach. (B) A taper pin awl is used to locate the piriformis fossa and the femoral canal.
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the wound and do not obscure the surgeon’s view. It is preferable to keep to a minimum the number of retractors that are inside the wound at any one time, and for this reason the use of flanged retractors may be helpful (Fig. 5A). The flanges allow retraction of surrounding soft tissue when the handle is rotated about the axis of the retractor point, and they are therefore more efficient than standard retractors. Several of the retractors also have the capability for the attachment of an additional light source. The reduced length of incision inevitably leads to a reduction in the delivery of light to the surgical field, and these additional light sources can provide considerable assistance in this respect. Preparation of the acetabular surface using straight reamer shafts may be a problem in MIS hip arthroplasty, particularly in the larger patient in whom soft tissue impingement may impede the surgeon and predispose to reaming in an abducted position. The
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use of a curved reamer shaft (Fig. 5B) that accommodates the soft tissues in the middle portion while the reamer face and handle end remain aligned may avoid this problem and allow proper acetabular preparation. The use of an angled reamer shaft (Fig. 5C) is an alternative approach in which the handle is orientated vertically and the correct abduction angle is built into the shaft. Access for the reamer face may be restricted by the small incision, especially when the larger reamers are used. Repeated passage of standard reamers through small incisions may abrade the soft tissues, predisposing to wound healing problems and infection. This has been addressed through the development of specialized reamers that have a reduced area of cutting, either by cutting down the reamer or by having blunt areas of the hemisphere (Fig. 5D), and this allows the reamer to be passed through the wound while minimizing soft tissue trauma. When introducing the
Fig. 5. Instruments for minimally invasive total hip arthroplasty. (A) Angled flanged retractors are efficient in clearing soft tissue when twisted about the axis of their points. (Courtesy of Stryker Canada, Ottawa, Ontario, Canada; with permission.) (B) A curved acetabular reamer and impactor can accommodate soft tissues. (C) An angled reamer is an alternative approach to overcome soft tissue impingement. (Courtesy of Centrepulse Orthopedics Inc., Austin, TX; with permission.) (D) Modifications made to the reamer face to reduce trauma to skin edges. (E) Angled acetabular impactor. ( F) Two designs of femoral elevator. ( G) The femoral reamers are notched so that insertion depth can be controlled using fluoroscopy. (H) Side entry mechanism for easy application of trial femoral heads.
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Fig. 5 (continued).
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acetabular component, use of a straight impactor may suffer from the same drawbacks as the use of a straight reamer shaft during reaming, but these difficulties can be overcome through the use of angled instruments, many of which have built-in alignment guides to optimize cup position (Fig. 5E). Exposure of the femoral shaft using the minimal incision posterior and anterolateral approaches may be optimized through the use of a femoral elevator (Fig. 5F) that delivers the femur into the wound while the flanges protect surrounding soft tissue. Further preparation of the femoral canal requires no special instruments. Preparation of the femoral canal using the two-incision technique is done under fluoroscopic guidance. Notches on the reamers, easily visualized by fluoroscopy, assist in guiding the extent and depth of reaming (Fig. 5G). The metaphyseal part of the femur can be prepared using standard broaches inserted through this incision, and introduction of the femoral stem requires no additional instrumentation. Insertion of trial femoral heads through these smaller incisions can be awkward and time consuming, and the use of side loading trial heads (Fig. 5H) may make this step easier.
Summary The term minimally invasive hip replacement encompasses a diverse range of surgical approaches through which hip replacement may be performed. These surgical approaches are technically demanding and are best performed using specially designed instruments that help to compensate for the reduced surgical exposure. The early results using these techniques are encouraging, although the literature is lacking evidence from well designed prospective trials comparing MIS techniques with standard approaches. The studies that exist suggest that patient satisfaction is high, bleeding may be reduced, recovery of function may be faster, and there may be the potential to reduce lengths of hospital stay, and all this may be achieved without increasing complication rates. These results, however, have been achieved by a small number of high-volume surgeons, and the authors feel it is essential that as these techniques are introduced into widespread practice the results be studied carefully.
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[17] Goldstein WM, Gordon AC, Branson JJ, Berland K. Minimal incision total hip arthroplasty [scientific exhibit no. SE204]. In: 70th Annual Meeting Proceedings of the American Academy of Orthopaedic Surgeons. New Orleans: American Academy of Orthopaedic Surgeons; 2003. p. 652 – 3. [18] Dorr LD. Mini-incision for THA: pros, cons and experience to date. In: Proceedings of the 31st Open Meeting of the Hip Society. New Orleans: American Academy of Orthopaedic Surgeons; 2003. p. 18. [19] Kennon RE, Keggi JM, Wetmore R, Zatorski LE, Keggi KJ. Total hip arthroplasty using the minimally invasive anterior surgical approach [scientific exhibit no. SE202]. In: 70th Annual Meeting Proceedings of the American Academy of Orthopaedic Surgeons. New Orleans: American Academy of Orthopaedic Surgeons; 2003. p. 652. [20] Swanson TV, Hanna RS. Advantages of cementless THA using mini-incision surgical technique [poster no. P043]. In: 70th Annual Meeting Proceedings of the American Academy of Orthopaedic Surgeons. New Orleans: American Academy of Orthopaedic Surgeons; 2003. p. 369 – 70. [21] Chimento GF, Sculco TP. Minimally invasive total hip arthroplasty. Operative Tech Orthop 2001;11(4): 270 – 3. [22] Wenz JF, Gurkan I, Jibodh SR. Mini-incision total hip arthroplasty: a comparative assessment of perioperative outcomes. Orthopedics 2002;25(10):1031 – 43. [23] DiGioia AM, Plakseychuck AY, Levison TJ, Jaramaz B. Mini-incision technique for total hip arthroplasty with navigation. J Arthroplasty 2003;18(2):123 – 8. [24] Salmon P, Hall GM, Peerbhoy D, Shenkin A, Parker C. Recovery from hip and knee arthroplasty: patients’ perspective on pain, function, quality of life, and wellbeing up to 6 months postoperatively. Arch Phys Med Rehab 2001;82(3):360 – 6. [25] Arslanian C, Bond M. Computer assisted outcomes research in orthopedics: total joint replacement. J Med Sys 1999;23(3):239 – 47. [26] Strassels SA, Chen C, Carr DB. Postoperative analge-
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sia: economics, resource use, and patient satisfaction in an urban teaching hospital. Anesth Analg 2002;94(1): 130 – 7. Mathias JM. MIS total hip implant speeds recovery. OR Manager 2001;17(12):5 – 7. Sivananthan DKS, Sivananthan S, Egan M, Warnke PH, Sherry E. Minimal invasive surgery for hip replacement using the NILNAV hip system [poster no. P512]. In: 70th Annual Meeting Proceedings of the American Academy of Orthopaedic Surgeons. New Orleans: American Academy of Orthopaedic Surgeons; 2003. p. 533. Metz CM, Freiberg AA. An international comparative study of total hip arthroplasty cost and practice patterns. J Arthroplasty 1998;13(3):296 – 8. Saleh KJ, Gafni A, Saleh L, Gross AE, Schatzker J, Tile M. Economic evaluations in the hip arthroplasty literature: lessons to be learned. J Arthroplasty 1999; 14(5):527 – 32. Maniadakis N, Gray A. Health economics and orthopaedics. J Bone Joint Surg [Am] 2000;82B(1):2 – 8. Healy WL, Iorio R, Richards JA, Lucchesi C. Opportunities for control of hospital costs for total joint arthroplasty after initial cost containment. J Arthroplasty 1998;13(5):504 – 7. Forrest GP, Roque JM, Dawodu ST. Decreasing length of stay after total joint arthroplasty: effect on referrals to rehabilitation units. Arch Phys Med Rehab 1999; 80(2):192 – 4. Healy WL, Ayers ME, Iorio R, Patch DA, Appleby D, Pfeifer BA. Impact of a clinical pathway and implant standardization on total hip arthroplasty: a clinical and economic study of short-term patient outcome. J Arthroplasty 1998;13(3):266 – 76. Hardinge K. The direct lateral approach to the hip. J Bone Joint Surg [Am] 1982;64B:17 – 9. Light TR, Keggi KJ. Anterior approach to hip arthroplasty. Clin Orthop 1980;152:255 – 60. Masterson EL, Masri BA, Duncan CP. Surgical approaches in revision hip replacement. J Am Acad Orthop Surg 1998;6:84 – 92.
Minimally invasive hip replacement: rationale, applied anatomy, and instrumentation Jonathan R. Howell, FRCS(Tr&Orth), Donald S. Garbuz, MD, MHSc, FRCS(C)*, Clive P. Duncan, MD, MSc, FRCS(C) University of British Columbia, Room 3114, 910 West 10th Avenue, Vancouver, British Columbia, V5Z 4E3, Canada
The last three decades have seen the development of minimally invasive surgery (MIS) techniques in a range of specialties, including abdominal surgery, thoracic surgery, and neurosurgery. Orthopedics has been no exception, with MIS techniques used to perform operations on several joints, such as the knee, shoulder, wrist, ankle, and hip. In the hip, arthroscopic techniques have been used for the treatment of labral tears [1 – 3], instability [4,5], infection [6,7], and the removal of loose and foreign bodies [8 – 10]. The arthroscope also has been used to assess polyethylene wear of total hip replacements [11] and as an adjuvant tool for visualization of the femoral canal during revision hip arthroplasty [12]. In recent years advances in operative techniques and instrumentation have allowed surgeons to perform total hip arthroplasty (THA) through incisions much smaller than those used previously. The definition of what constitutes MIS hip arthroplasty has yet to be finalized, but at present, the term MIS THA may be applied to any hip replacement procedure in which the length of the wound and the surgical access are deliberately modified in an attempt to reduce the tissue trauma associated with hip replacement, with most investigators reporting wounds of 10 cm length or less [13 – 20]. The minimum length of the inci-
Jonathan R. Howell was supported by a grant from The John Charnley Trust. * Corresponding author. E-mail address: [email protected] (D.S. Garbuz).
sion that can be used without skin stretch is determined by the diameter of the acetabular component that is to be used. For the cup to be inserted without touching or stretching the skin edges, the length of the incision must be equal to at least half the length of the cup circumference, because each skin flap must pass around one half of the component. Based on an acetabular component diameter of 56 mm, Goldstein [17] has estimated that a 4-inch incision is required to avoid contact between the cup and the subcutaneous fat. Several techniques of MIS hip arthroplasty have been described [16 – 23], and the authors have found it useful to divide the various MIS approaches into two main categories: the minimal incision approaches and the two-incision approach. The minimal incision approaches are modifications of the standard posterior, anterolateral, and anterior approaches that are used commonly for hip arthroplasty and are performed through wounds 7 – 10 cm in length. The two-incision approach constitutes a new approach for hip replacement, using intermuscular planes to gain access to the hip joint and minimizing the dissection of muscles and tendons. Whichever technique is used, the reduced length of incision and the reduced dissection mean that exposure may be difficult using standard instruments. The development of MIS hip arthroplasty therefore has been accompanied by the development of specialized instruments designed to facilitate exposure and bony preparation. In this article the authors review the rationale, surgical anatomy, and instrumentation of MIS THA.
0030-5898/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/S0030-5898(03)00112-3
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Rationale for minimally invasive hip replacement Advantages for patients MIS techniques have the potential to benefit patients in several ways, as a consequence of the reduced dissection associated with the surgical access. In the medium to long term, hip arthroplasty using conventional surgical techniques has been shown to produce improvements in pain, function, mood, general health, and quality of life [24,25], but the postoperative period remains one characterized by pain and reduced function [26]. Through a reduction in the degree of tissue disruption, MIS hip arthroplasty has the potential to reduce perioperative blood loss and pain in the immediate postoperative period and to preserve muscle function, thereby leading to an earlier recovery of normal activities [23,27] and an earlier discharge from the hospital. Several studies [14,17,20,22,23] have found a reduction in the estimated blood loss following MIS THA, although this is not a universal finding [15], and the reliability of estimated blood loss as a measurement tool is open to question. Indeed, Goldstein [17] found that although estimated blood loss was significantly less in patients undergoing MIS THA, the postoperative hemoglobin tended to be higher in their control group ( P = 0.05) and there was no difference in the transfusion requirements between the two groups. DiGioia et al [23] selected 33 mini-incision patients from their cohort of 121 and compared these to matched control subjects. They found that using a postoperative hematocrit measurement of 0.28 as the indication for transfusion, the mini-incision group of patients received a mean 0.7 units of blood, compared with 1.1 units in the control group (P < 0.05). Similarly, Wenz et al [22] found that MIS patients required a mean of 0.3 units of blood, compared with 0.6 units for control subjects who had their operation performed through an anterolateral approach ( P = 0.006). Although both of these studies demonstrated statistically significant results, however, the clinical significance of these differences is questionable. There is little in the literature to support the contention that MIS THA is associated with less pain. Chimento et al [14] found no difference in narcotic requirements in their randomized controlled trial. Swanson and Hanna [20] defined ‘‘problem pain’’ as deviation from their standard postoperative pain management protocol. They found that no MIS patients suffered from ‘‘problem pain’’ compared with 12% of the control patients ( P < 0.001), but the use of historical control subjects in this study has the
potential to introduce bias into their results. Dorr [18] has described in detail the pain and analgesia requirements of 90 patients undergoing MIS THA, but without control subjects the results are difficult to interpret. The recovery of function has been studied more extensively, with many positive results. Wenz et al [22] found that their MIS patients ambulated significantly sooner in the postoperative period ( P = 0.02), but the mean length of stay was similar in both groups. That study compared MIS posterior approach with a standard length incision lateral approach, and the recovery of ambulation may owe as much to the approach as to the incision. Chimento et al [14] found that significantly fewer of their MIS patients limped at 6 weeks ( P < 0.04), but there was no difference in the length of hospital stay, and DiGioia et al [23] reported similar findings, with patients showing significantly higher Harris Hip Scores 3 months ( P = 0.45) and 6 months ( P = 0.17) after mini-incision THA. They found that there was no difference in the mean length of hospital stay between mini-incision and standard incision patients; this also was confirmed by Wright et al [15]. Swanson and Hanna [20] found that MIS patients made a faster return to full activity ( P < 0.001), and Berger [16], Dorr [18], and Sherry [28] have all reported favorable recovery of postoperative function with short lengths of stay, but in each of these last three studies there was no control group for comparison. DiGioia et al [23] found no differences in the functional outcome in their two groups 1 year after surgery. There are cosmetic advantages to the use of the smaller incisions of the MIS technique and this may be a factor that propels MIS hip arthroplasty into widespread orthopaedic practice. Three studies [15, 17,18] have reported favorable patient attitudes toward the scars that result from MIS THA, and indeed Wright et al [15] concluded that ‘‘this investigation confirms no dramatic clinical benefit of an abridged surgical approach other than cosmetic appeal to the patient.’’ Advantages for health care providers MIS holds several potential advantages for institutions and individuals providing orthopaedic care. In other fields of surgery the introduction of MIS techniques has radically reduced recovery times and lengths of hospital stay, and as surgeons face pressures to reduce length of stay and hospital costs [29], MIS hip arthroplasty may assist toward these goals. The influence of length of hospital stay on total cost is, however, controversial, and the orthopaedic
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literature is deficient in well designed economic evaluations of different surgical strategies in hip arthroplasty [30,31]. Healy et al [32] have shown that almost 80% of total hospital costs associated with the provision of THA are generated within the first 48 hours of admission; in the operating room, recovery room, pharmacy, and in postoperative nursing costs. In their study they found that the cost of the first hospital day was the most expensive at $6,343, which constituted 68.25% of the total costs, and these costs reduced dramatically to $188 by the sixth day of hospital admission. To have a major effect on the total costs of providing a hip arthroplasty service, MIS techniques therefore will need to reduce hospital length of stay to less than 48 hours, and even then many of the costs remain fixed. There are reports of day care hip arthroplasty [16,27] using MIS techniques, but it is unclear at this stage whether this will become a reality for most patients. Indeed, efforts to achieve this may increase referral rates to rehabilitation units, particularly for elderly patients, patients who live alone, and those with comorbid conditions [33]. The economic benefits of MIS hip arthroplasty therefore remain unproven at the present time. Healy [34] found that the introduction of a clinical pathway and a hip implant standardization program have in themselves led to a substantial reduction in length of stay and hospital costs without adversely affecting outcomes. The orthopaedic community must study carefully the effect that the introduction of MIS techniques has on the health economics of THA over and above the effects of introducing well designed care pathways that facilitate early discharge from hospital. A more detailed economic analysis is presented in a separate article in this issue. Potential disadvantages of minimally invasive hip replacement
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found that surgical times using MIS techniques were slightly shorter than in a cohort of control patients (P < 0.02), but the MIS patients in this study weighed less than control subjects (P < 0.03). Swanson and Hanna [20] showed that MIS surgery was faster (P < 0.0001), but in this study they compared cementless THA through an MIS approach with historical control subjects who had hybrid THAs. Wenz et al [22] also have shown reduced surgical times with the MIS posterior approach. The MIS patients were a single-surgeon series, however, whereas the control subjects were not, and the mean surgical time for primary THA in the control group was 164 minutes. Although the authors have not experienced problems, the use of unfamiliar approaches and instruments may lead to an increase in early complications, such as neurovascular injuries, infections, thromboembolism, and component malposition. This last complication then may lead to longer-term complications, such as instability, osteolysis, and loosening. Several studies [14,15,17,20,22] have failed to show any difference in the rates of these complications, and at present these concerns remain theoretic. It is the authors’ opinion that, although this surgical technique is in its infancy, it should be performed only by surgeons who are experienced in hip replacement through open techniques, and it is essential that the rates of complications be monitored carefully.
Surgical anatomy and instrumentation of minimally invasive surgery hip arthroplasty Full descriptions of the techniques used for the various approaches are provided in other articles in this issue, and so the authors shall describe here only anatomic issues as they pertain to each approach. Minimal posterior approach
The introduction of a new surgical technique always has the potential for disadvantages and advantages, and MIS hip arthroplasty is no exception. In the authors’ experience of using the two-incision technique there is an initial learning curve during which the surgical duration is longer than normal for primary total hip replacement, but with experience the operating time can be reduced. This also has been the experience of others [16]. Several studies have addressed the issue of operative time using the minimal posterior approach. Chimento et al [14] found no difference in the mean operative time between MIS patients and control subjects in their prospective randomized trial, and this result is supported by the findings of Goldstein et al [17]. Wright et al [15]
The position of the skin incision for the minimal posterior approach differs slightly between investigators. The authors use a 7 – 10-cm incision placed along the posterior aspect of the greater trochanter with 70% of the incision placed distal to the tip of the greater trochanter and 30% proximal to it (Fig. 1A), similar to the approach described by Chimento and Sculco [21]. Dorr [18] advocates the use of a 5 – 10-cm straight incision along the posterior border of the greater trochanter from a point proximally level with the tip of the greater trochanter to a point distally that is level with the vastus tubercle of the femur. Goldstein [17] draws his standard incision on the skin and then uses this to guide the incision for
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Fig. 1. Minimal incision posterolateral approach to the left hip. (A) Skin markings showing greater trochanter and the planned skin incision. (Courtesy of Zimmer Inc., Warsaw, IN; with permission.) (B) Diagram showing position of retractors for acetabular exposure (C) Skin incision for the posterior approach described by Sherry [13,28]. (Courtesy of Dr. E. Sherry, Sydney, New South Wale, Australia.) (D) The neck osteotomy is made in situ using a cutting block. (Courtesy of Dr. E. Sherry, Sydney, New South Wale, Australia.) (E) The ‘‘lollipop’’ device is used to insert the acetabular component. (Courtesy of Dr. E. Sherry, Sydney, New South Wale, Australia.)
the minimal approach. A 4-inch incision is planned 2 – 3 cm posterior to the apex of the standard incision between the two endpoints of the longer incision. This new incision also is moved 2 cm posterior and superior toward the posterior – inferior spine of the
pelvis. Swanson [20] has described a 10-cm incision, the starting point of which is located by measuring 4 cm distal to the tip of the greater trochanter along the line of the femur, and then measuring 4 cm posterior to the femur. From this point the incision
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is made in a proximal direction, angled posteriorly at 20° to the line of the femur. DiGioia [23] plans his incision with the affected leg placed in 70° – 80° of flexion. An 8 – 12-cm incision is made in line with the shaft of the femur, with two thirds of the incision lying proximal to the tip of the greater trochanter and one third distal to it. The common principle underlying all these incisions is the creation of a mobile window that can be moved to different positions during different stages of the operation. After the incision, the anatomy of the approach is similar to a standard posterior approach, but the small incision means that great care should be taken to protect soft tissues when using power instruments. Adequate acetabular exposure requires precise placement of retractors (Fig. 1B), the first of which is placed over the anterior column and retracts the femoral metaphysis anteriorly; to mobilize the femur sufficiently it may be necessary to incise the inferior capsule down to the transverse acetabular ligament. A second retractor is placed over the posterior lip of the acetabulum, and with care to avoid injury to the sciatic nerve, retracts the posterior tissues. If necessary a third retractor may be placed underneath the cotyloid notch. This retractor should be removed at the time of cup insertion. To expose the femur, the acetabular retractors are removed and then the dependent leg is moved into 30° – 45° of flexion, maximum adduction, and 90° of internal rotation. A femoral elevator is placed under the femoral neck, thus delivering the proximal femur into the wound. Placement of a retractor along the medial aspect of the calcar further improves access for preparation of the femoral canal. A gluteus medius retractor is also potentially helpful in allowing a properly lateralized entry point in the proximal femur. Sherry described the use of an alternative posterior approach for MIS THA that avoids dislocation of the hip joint before neck osteotomy and that may, therefore, reduce soft tissue disruption [13,28]. A 5-cm incision is made starting one fingerbreadth behind the prominence of the greater trochanter and curved backward at 45° to the long axis of the femur (Fig. 1C). The approach is similar to that used by other investigators, except that the quadratus femoris is left intact and a posterior capsulectomy is performed to expose the femoral neck. A cutting block then is used to guide the osteotomy, which is made with the hip in situ followed by removal of the head (Fig. 1D). The position of the incision makes access to the proximal femur easy, but exposure of the acetabulum may be more limited. This is overcome through the use of specialized angled reamers and a
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‘‘lollipop’’ positioning device for insertion of the acetabular component (Fig. 1E). Minimal anterolateral approach: technique and applied anatomy The minimal anterolateral approach is a modification of the anterolateral approach described by Hardinge et al in 1982 [35]. The surgeon first marks the tip and then the anteroposterior midline of the greater trochanter. A point is then measured along this midline, 2 cm distal to the tip of the trochanter, and this point becomes the midpoint of the incision. A 3-inch incision is then marked, extending 1.5 inches either side of the midpoint, at an angle of 30° – 45° with the long access of the femur (Fig. 2A). The fascia lata then is divided in the line of its fibers and not in line with the initial incision. The remaining anatomy is similar to the standard anterolateral approach, but again, acetabular exposure depends on accurate placement of retractors. The first retractor is placed over the posterior – inferior border of the acetabulum and retracts the femur posteriorly. Placement of this retractor is assisted by flexion, adduction, and external rotation of the hip. A second retractor is placed over the anterior superior aspect of the acetabulum and retracts the gluteus medius and minimus tendons, and if necessary a third retractor is placed over the anterior inferior acetabular margin, which retracts the psoas tendon and completes the acetabular exposure (Fig. 2B). To expose the femur, the acetabular retractors are removed and the hip is flexed adducted and externally rotated. A femoral elevator is placed under the femoral neck to deliver the femur into the wound, and a second retractor is placed in the piriformis fossa to retract the gluteus medius tendon. Finally, a retractor is placed along the medial calcar to retract the vastus lateralis, resulting in clear exposure of the femoral canal (Fig. 2C). Minimal anterior approach The MIS anterior approach is a modification of the Smith-Peterson approach that uses an intermuscular, internervous plane to gain access to the anterior aspect of the hip joint. Keggi [19,36] has described making a 5 – 8-cm curved incision, with its convexity placed laterally, from a point just distal to the anterior superior iliac spine extending to the anterior border of the greater trochanter. The deep dissection is through a plane between tensor fascia lata (superior gluteal nerve) and the sartorius (femoral nerve), and then deep to this, the dissection is extended between the
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Fig. 2. Minimal incision anterolateral approach to the right hip. (A) Anatomic landmarks for the skin incision. (Courtesy of Zimmer Inc., Warsaw, IN; with permission.) (B) Intraoperative photograph showing the acetabular exposure that can be achieved using the minimal incision anterolateral approach. (C) Intraoperative photograph showing femoral exposure.
rectus femoris (femoral nerve) medially and gluteus medius (superior gluteal nerve) laterally, which exposes the anterior aspect of the hip joint capsule. The structures at risk from this approach are the lateral cutaneous nerve of the thigh and the lateral circumflex femoral artery [37]. To avoid injury to the lateral cutaneous nerve of the thigh, Keggi recommends dissecting through the anterior border of tensor fascia lata and retracting the anterior border medially. The approach affords good exposure of the acetabulum, and in most patients reaming may be performed through this incision using a straight reamer. In larger patients access is difficult, however, and Keggi describes the use of a separate stab incision through which the surgeon may pass the reamer handle and later the shell impactor in a retrograde direction before use of the instrument. In the past the anterior approach has been considered to give inadequate exposure of the femoral canal [37]. Keggi states that this may be overcome by extreme external rotation of the femur and placement of a bone hook around the femur at the level of the
lesser trochanter, which is then used to deliver the femur into the wound. Placing a small sandbag centrally under the sacrum before the start of the operation helps with the leg extension that is required for this maneuver, but the surgeon must be careful that this does not alter the position of the acetabular component when that is inserted. In some cases this maneuver is not sufficient to expose the femoral canal, in which case the exposure can be improved by dividing the posterior capsule and dissection of the short external rotators from the posterior aspect of the proximal femur [19], although such dissection undertaken without repair of the posterior tissues seems to contradict the principles of tissue preservation inherent in the MIS approach. Two-incision minimally invasive approach The two-incision approach was described by Berger et al following on the work of Mears [16], who initially developed this technique. The principle of the approach is two incisions, one for the acetab-
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ulum and one for the femur, avoiding the division of muscle or tendons, thereby aiming to achieve a faster recovery of normal function. To guide the incision, the anterior – superior iliac spine and the tip of the greater trochanter are marked on the sterile drapes. The femoral neck lies approxi-
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mately three fingerbreadths distal to the line that connects these two marks, and its position is confirmed using fluoroscopy. The 2-inch incision is marked along this line extending on the fluoroscopy image from the head – neck junction to the intertrochanteric line (Fig. 3A). After the incision, the dis-
Fig. 3. Acetabular exposure using the two-incision minimally invasive approach. (A) The femoral neck lies three fingerbreadths distal to a line joining the anterior – superior iliac spine and the tip of the greater trochanter. The anterior skin incision is marked using fluoroscopy to guide the position. (B) The deep fascia is incised to reveal the underlying tensor fascia lata. (C) Tensor fascia lata is retracted to reveal rectus femoris. (D) Artery forceps have been placed under branches of the lateral femoral circumflex artery, which must be cauterized. (E) The neck osteotomy is made in situ and a ‘‘hockey puck’’ segment of the head and neck junction is removed.
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section is similar to the minimal incision anterior approach (Figs. 3B – D). The hip joint capsule is exposed by placing retractors over the superolateral aspect of the femoral neck, inferomedial to the neck and over the front of the capsule heading medially to engage the anterior column. The assistant moves the hip joint to confirm the joint line and then an H-shaped capsulotomy is made with elevation of the flaps for later repair. The lip of the acetabulum is exposed and the retractors are replaced inside the capsule and around the neck of the femur to expose the head – neck junction of the femur. The hip usually cannot be dislocated at this stage and instead the neck osteotomy is made in situ. This is best done as two osteotomies, the first of which is made at the head – neck junction. The second osteotomy is made further down the neck and the intervening ‘‘hockey puck’’ section of the neck is removed using a Schanz pin (Fig. 3E). This allows removal of the remaining femoral head from the socket, and the acetabulum is exposed by placing one retractor over the anterior column, one over the posterior lip of the acetabulum, and a third placed anteroinferior to the acetabulum. To access the femur, the surgeon passes a piriformis fossa guide or an index finger from the back of the proximal femur around the posterior aspect of the gluteus medius pointing proximally and posteriorly
into the buttock. A 2-cm transverse incision is marked on the skin over the guide or the surgeon’s finger if this is used instead (Fig. 4A). The surgeon’s second index finger then passes through this incision to find the piriformis fossa and a taper pin awl is guided to the piriformis fossa and starts the entry point in the femoral canal (Fig. 4B). Once the initial entry point is made, the femur is prepared using reamers and rasps inserted through the posterior incision, using fluoroscopy to guide depth of insertion of the instruments and to confirm their correct alignment. The ideal location of this incision and the subsequent plane through the soft tissues is between the posterior border of the gluteus medius and the piriformis, down to their femoral attachments. Instrumentation for minimally invasive hip replacement Performing MIS hip replacement is challenging, but the difficulties of the operation can be reduced if instruments developed for the technique are used. Achieving the correct exposure is one of the major challenges, for which several companies have developed specialized retractors. These retractors have long handles, angled at approximately 90° to the blade, so that the assistant’s hands are kept at a distance from
Fig. 4. Femoral exposure using the two-incision minimally invasive approach. (A) Marking the incision for the femoral approach. (B) A taper pin awl is used to locate the piriformis fossa and the femoral canal.
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the wound and do not obscure the surgeon’s view. It is preferable to keep to a minimum the number of retractors that are inside the wound at any one time, and for this reason the use of flanged retractors may be helpful (Fig. 5A). The flanges allow retraction of surrounding soft tissue when the handle is rotated about the axis of the retractor point, and they are therefore more efficient than standard retractors. Several of the retractors also have the capability for the attachment of an additional light source. The reduced length of incision inevitably leads to a reduction in the delivery of light to the surgical field, and these additional light sources can provide considerable assistance in this respect. Preparation of the acetabular surface using straight reamer shafts may be a problem in MIS hip arthroplasty, particularly in the larger patient in whom soft tissue impingement may impede the surgeon and predispose to reaming in an abducted position. The
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use of a curved reamer shaft (Fig. 5B) that accommodates the soft tissues in the middle portion while the reamer face and handle end remain aligned may avoid this problem and allow proper acetabular preparation. The use of an angled reamer shaft (Fig. 5C) is an alternative approach in which the handle is orientated vertically and the correct abduction angle is built into the shaft. Access for the reamer face may be restricted by the small incision, especially when the larger reamers are used. Repeated passage of standard reamers through small incisions may abrade the soft tissues, predisposing to wound healing problems and infection. This has been addressed through the development of specialized reamers that have a reduced area of cutting, either by cutting down the reamer or by having blunt areas of the hemisphere (Fig. 5D), and this allows the reamer to be passed through the wound while minimizing soft tissue trauma. When introducing the
Fig. 5. Instruments for minimally invasive total hip arthroplasty. (A) Angled flanged retractors are efficient in clearing soft tissue when twisted about the axis of their points. (Courtesy of Stryker Canada, Ottawa, Ontario, Canada; with permission.) (B) A curved acetabular reamer and impactor can accommodate soft tissues. (C) An angled reamer is an alternative approach to overcome soft tissue impingement. (Courtesy of Centrepulse Orthopedics Inc., Austin, TX; with permission.) (D) Modifications made to the reamer face to reduce trauma to skin edges. (E) Angled acetabular impactor. ( F) Two designs of femoral elevator. ( G) The femoral reamers are notched so that insertion depth can be controlled using fluoroscopy. (H) Side entry mechanism for easy application of trial femoral heads.
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Fig. 5 (continued).
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acetabular component, use of a straight impactor may suffer from the same drawbacks as the use of a straight reamer shaft during reaming, but these difficulties can be overcome through the use of angled instruments, many of which have built-in alignment guides to optimize cup position (Fig. 5E). Exposure of the femoral shaft using the minimal incision posterior and anterolateral approaches may be optimized through the use of a femoral elevator (Fig. 5F) that delivers the femur into the wound while the flanges protect surrounding soft tissue. Further preparation of the femoral canal requires no special instruments. Preparation of the femoral canal using the two-incision technique is done under fluoroscopic guidance. Notches on the reamers, easily visualized by fluoroscopy, assist in guiding the extent and depth of reaming (Fig. 5G). The metaphyseal part of the femur can be prepared using standard broaches inserted through this incision, and introduction of the femoral stem requires no additional instrumentation. Insertion of trial femoral heads through these smaller incisions can be awkward and time consuming, and the use of side loading trial heads (Fig. 5H) may make this step easier.
Summary The term minimally invasive hip replacement encompasses a diverse range of surgical approaches through which hip replacement may be performed. These surgical approaches are technically demanding and are best performed using specially designed instruments that help to compensate for the reduced surgical exposure. The early results using these techniques are encouraging, although the literature is lacking evidence from well designed prospective trials comparing MIS techniques with standard approaches. The studies that exist suggest that patient satisfaction is high, bleeding may be reduced, recovery of function may be faster, and there may be the potential to reduce lengths of hospital stay, and all this may be achieved without increasing complication rates. These results, however, have been achieved by a small number of high-volume surgeons, and the authors feel it is essential that as these techniques are introduced into widespread practice the results be studied carefully.
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