Posterior Minimally Invasive Surgery Approach for Total Hip Arthroplasty

Transcription

1 53 Posterior Minimally Invasive Surgery Approach for Total Hip Arthroplasty T.P. Vail Introduction The popularity of the minimal incision posterior approach among many arthroplasty surgeons reflects the desire for an increasingly more tissue-preserving, rapid, and highly functional recovery after total hip replacement. Many surgeons have settled on the posterior approach after experience with other approaches. The surgical exposures for hip arthroplasty used over the years have included the direct lateral, the anterior, the antero-lateral with modifications, and the posterior approach. Each approach provided optimal access to the hip joint with the available instrumentation and implants of the time. The enduring feature of the posterior approach has been the easy access to the joint and a low incidence of limp due to the sparing of the abductor attachments [1]. The lateral Charnley approach facilitated the Charnley surgical technique, but was associated with occasional trochanteric non-union, dislocation, and a programmed slow recovery [2]. The anterior approach provided excellent acetabular exposure, but a more complicated access to the femoral shaft, particularly with the early straight-stemmed implants [3, 4]. The direct lateral and modified lateral approaches have been associated with an incidence of limp or abductor lurch and a slower recovery due to the need to protect the abductor mechanism [5]. The downside of the posterior approach historically has been a higher rate of dislocation [6, 7], especially when using a smaller prosthetic femoral head size. However, improvements in bearing function and refinement in surgical technique have brought the return of larger diameter articulations and recognition of the importance of capsular repair, allowing the posterior approach to evolve into a highly functional and highly stable approach for total hip arthroplasty [8]. The posterior approach to the hip was originally described as a technique for inserting a proximal femoral hemi-arthroplasty [9]. However, variations of the technique have also been useful for access to the sciatic nerve, the posterior column, the piriformis tendon, the lateral rim of the acetabulum, as well as the hip joint itself. Variously termed the posterior, Southern, dorsal, and posterolateral approach, related to nuances in the deeper dissection, the descriptions by all the names share the same pathway through the gluteus maximus muscle and behind the gluteus medius muscle in order to gain entry into the hip joint. More recent evolution of the posterior approach centers on the development of smaller incisions, minimally invasive techniques, and rapid recovery [10 12]. The term»evolution«best describes the present status of the minimal incision posterior approach which has been adapted from the standard posterior exposure. The muscular and nervous interval is the same as the classic descriptions, with the exception of some subtle variation which will be described in this chapter. The size of the incision and the intentional preservation of soft tissue structures distinguish the minimally invasive posterior approach from a standard approach. The minimal incision approach eliminates all parts of the standard approach that are not necessary to perform a total hip arthroplasty with the use of lower profile instruments and modern total hip implants.

2 406 Part IV B Minimally Invasive Surgery: Total Hip Arthroplasty Methods Positioning and Planning the Skin Incision 53 The surgical technique is performed with the patient in the lateral decubitus position. All downside pressure points are padded, and an axillary roll is placed under the thorax for additional protection of the shoulder and brachial plexus. Some type of pelvic positioning device is generally used to stabilize the pelvis which tends to shift when the patient is moved from a supine to a lateral position [13]. Once the patient is properly positioned on the operating table, the operative extremity is prepped and draped in the usual sterile fashion, preferably with an adhesive, bacterostatic covering over the operative site ( Fig. 53.1). Placement of the skin incision is based upon palpation of the greater trochanter. The hip is flexed 45 degrees, and adducted 10 degrees during the planning of the skin incision. The incision is placed one-third below the tip of the trochanter, and two-thirds above the tip of the trochanter. The length of the incision will be dependant upon the depth of the subcutaneous fat, with a deeper fat layer requiring a longer incision in order to access both the acetabulum and the femoral shaft. The incision may start out short, and can be lengthened during the operation as needed in order to avoid tension on the skin edges during the preparation of the bone and introduction of the implants. The surgeon may choose to bring the incision across the trochanter toward the anterior edge of the vastus lateralis ridge at the base of the greater trochanter, or stay behind the trochanter parallel to the posterior border of the femur depending upon the position of the leg on the operating table. When the hip is more flexed, the skin incision will appear more posterior. With the hip in a more neutral position, the incision will cross the trochanter. In either case, the important consideration is to place the incision over the acetabulum, with the trochanter serving as a superficial landmark that one can palpate in order to orient and locate the incision properly. The direction of the skin incision is oblique, running perpendicular to the face of the acetabulum and thereby in line with the handle of the reamer that will be used to prepare the acetabulum at a later stage of the operation. Skin and subcutaneous tissue are sharply divided down to the fascia overlying the gluteus maximus muscle. Avoid finger dissection and unnecessary trauma to the fat layer, as the fat can be easily devascularized with blunt Fig Skin incision Fig Muscle-tendon junction of the gluteus maximus trauma. The investing fascia of the gluteus maximus is divided longitudinally in line with the direction of the fascial fibers and consequently, in line with the underlying gluteus maximus muscle fibers below the fascia. The fascial incision proceeds from the level of the sciatic notch proximally to the intersection of the tensor fascia distally. The sciatic notch can be palpated through the skin as a soft spot above the ischial tuberosity. The beginning of the tensor fascia corresponds with the muscle-tendon junction of the gluteus maximus muscle below the greater trochanteric ridge. There is no reason to extend the incision distally into the tensor fascia during the initial approach, as it has the potential to add to the morbidity of the recovery and may not be necessary for adequate exposure of the hip ( Fig. 53.2).

3 Chapter 53 Posterior Minimally Invasive Surgery Approach for Total Hip Arthroplasty The Deeper Approach and Capsular Incision The initial part of the deeper approach is really trans-muscular through the gluteus maximus muscle. The gluteus maximus muscle is divided bluntly in line with its fibers. It may be necessary to cut the investing fascia below the muscle with a scissors. Carefully control bleeding points within the muscle using electrocautery during the approach, but avoid cutting muscle fibers with electrocautery. Deeper exposure is achieved by placing a Charnley retractor carefully beneath the gluteus maximus muscle, applying the minimum tension required to provide visualization. In a small patient, a Charnley retractor may provide excessive soft-tissue pressure, especially with a particularly small incision. In such cases, it is wise to choose a smaller self-retaining device that applies less tension, or avoid a self-retaining retractor all together. Take care not to damage the gluteus medius muscle which lies below the gluteus maximus when placing a retractor into the incision. The deeper dissection begins with reflection of the trochanteric bursa. The bursa is incised sharply along the posterior edge of the gluteus medius muscle from a point just above the trochanteric insertion of the medius tendon proximally to the top of the quadratus femoris muscle distally. The bursa is well vascularized, and will require coagulation of bleeding points as it is mobilized. Once incised, the bursa can be pushed posteriorly with a sponge, thereby exposing the short external rotators of the hip. Overlying the short external rotators and the hip capsule is often located a plexus of veins that will also require coagulation in order to minimize bleeding later during the capsular incision. The sciatic nerve can be palpated at this point in the operation, lying below the piriformis (with some variation in approximately 10% of cases) [14] and on top of the short external rotators and ischial tuberosity in most cases. The sciatic nerve is protected throughout the duration of the procedure. The piriformis, conjoint tendon (obturator internus, externus, and gemelli muscles), and the posterior hip capsule are tagged with a suture to facilitate exposure and later repair during closure. Once the posterior capsule and external rotators are exposed, the next step in the exposure is the capsular incision ( Fig. 53.3). The capsular incision is a watershed point in the operation that distinguishes the more commonly described posterior approach from a dorsal approach []15. Exposure is facilitated by placing a blunt Homan retractor beneath the gluteus medius muscle and on Fig Capsular incision top of the gluteus minimus muscle around the front of the femoral neck. The posterior border of the gluteus medius muscle is gently elevated, avoiding tension on the superior gluteal neuro-vascular pedicle emerging from the greater sciatic notch, thereby exposing the interval between the superior edge of the piriformis and the inferior edge of the gluteus minimus muscle. The dorsal approach uses this interval to access the femoral canal with the femoral head in situ. To continue the posterior approach, the capsule is incised along the top of the piriformis tendon proceeding from the acetabular rim down to the piriformis fossa, and then distally along the intertrochanteric line to the top of the quadratus femoris muscle. If possible, the dissection stops above the top of the quadratus femoris, which contains branches of the medial femoral circumflex artery. Coagulate bleeding points within the hip capsule during exposure. A capusulo-tendinous flap consisting of the posterior hip capsule and the short external rotators is then reflected posteriorly with the use of the previously placed suture, thereby protecting the sciatic nerve and exposing the hip joint. The author s preference is to tag the capsule and external rotators as a single layer, but a separation of these structures is also quite acceptable. The L-shaped capsulotomy as described here maintains the integrity of the ischio-femoral ligament, providing the strength of the posterior hip capsule and the resistance to dislocation when repaired [16]. With the capsule incised, the femoral head is dislocated by flexion and internal rotation of the joint. Tension on the sciatic nerve during hip dislocation is avoided by

4 408 Part IV B Minimally Invasive Surgery: Total Hip Arthroplasty keeping the knee flexed at all times. The femoral neck is exposed by placing a slender retractor below the femoral neck to protect the posterior soft tissues. The neck of the femur is then osteotomized with an oscillating saw at a level determined by templating or navigation. The tip of the greater trochanter, the lesser trochanter, and the femoral neck are all clearly visible for registration within the surgical wound when computer navigation is utilized in conjunction with the mini-posterior approach. Once the femoral head is removed, the exposure of the acetabulum begins. 53 Acetabular Preparation and Exposure Fig Anterior acetabular retractor The minimal incision posterior approach allows a complete view of the entire circumference of the acetabulum. The acetabular exposure is created by translating the femur forward through a combination of leg positioning and capsular elevation. Optimal leg positioning for acetabular exposure is achieve by placing the hip in a position of 45 degrees of flexion and 10 degrees of adduction, thereby relaxing the anterior hip capsule. A retractor is then placed under the femoral neck and over the anterior lip of the acetabulum. The anterior acetabular retractor and the proximal femoral elevator are the key instruments used during the mini-posterior approach ( Fig. 53.4). Translation of the femur is further facilitated by elevating the anterior hip capsule fibers off of the anterior rim of the acetabulum with the anterior retractor providing some degree of tension on the capsular fibers. This capsular elevation can be accomplished with the use of electocautery, or sharply with a knife. Additionally, a radial cut in the inferior capsule will provide further relaxation of the soft tissues required to translate the femur anterior to the acetabulum during more difficult exposures wherein capsular elevation alone is not satisfactory to mobilize the femur. The transverse acetabular ligament may be left intact when the inferior capsule is divided. Branches of the obturator artery travel from within the pelvis into the fovea of the hip over the inferior edge of the acetabulum, and may require coagulation during exposure or later during reaming. With the anterior acetabular retractor in place, and traction on the posterior hip capsule, the entire acetabulum is in view. At this point the labrum is excised, the bony rim of the acetabulum is exposed, and osteophytes around the rim of the acetabulum can be removed. Likewise, the medial osteophyte commonly covering the fovea in osteoarthritic cases can be removed prior to further preparation of the acetabulum. The acetabulum is prepared for the implant by sequentially reaming with spherical reamers. A modified curved, or S-shaped acetabular reamer allows reaming without tension on the skin and soft tissues. Likewise, a modified cup inserter allow impaction of the acetabular component with a minimum of soft tissue tension. Femoral Preparation The proximal femur is exposed by placing a narrow retractor beneath the femoral neck to elevate the proximal femur and protect the posterior soft tissues. Placement of a sponge between the retractor and the skin edge distributes the pressure of the retractor over a larger surface area and helps to protect the skin edge. Femoral preparation can then proceed with confidence as the surgeon is able to see the proximal femur in its entirety. With satisfactory visualization, the femoral broaches and reaming devices can be properly lateralized and anteverted to create a stable prosthetic articulation with the acetabular component. A cemented or cementless implant can be inserted using any combination of reaming and broaching. Careful movement of the proximal femoral elevator and the leg will allow better visualization of the piriformis fossa or calcar femorale, depending upon the wishes of the surgeon and the stage of the operation, thereby assuring appropriate fit

5 Chapter 53 Posterior Minimally Invasive Surgery Approach for Total Hip Arthroplasty Fig Proximal femoral elevator and position of the implant while minimizing the risk of a calcar split or femur fracture ( Fig. 53.5). Implant Insertion It has been the habit of the author to obtain an intra-operative radiograph with the trial components in place prior to inserting the final components. The intra-operative radiograph can be used to determine that the implants chosen are appropriately sized, positioned, and matched to the desired amount of length, offset, and soft tissue tension. Additionally, the stability of the hip can be tested by removing all retractors with the trials in place, and checking the range of motion of the hip joint. If this assessment is performed during the operation, adjustments can be made prior to making the final choice of implants, thereby minimizing device wastage. When inserting the implants it is critically important to keep them from touching the edges of the wound and the skin. The skin, even when prepped, is a potential source of prosthetic bacterial contamination. Thus, it is worthwhile to make an effort to adjust retractors and move the leg in order to allow placement of the components within the operative site without running them across the skin edge in the process. The skin incision must be large enough to accommodate this process. Insertion of the femoral component may require flexion of the hip to place the component within the femoral canal initially, then once the trunion of the implant is within the wound, the implant is turned into the appropriate amount of anterversion to match the desired position of the component and the bone preparation. When using a particularly small incision, the neck of the prosthesis and the trunion may extend over the skin edge unless the implant is introduced into the wound in retroversion and then rotated to the appropriate position prior to the implant engaging the endosteum of the femur as it is pushed into the femoral canal. Mechanical lavage of the wound using a water pick type device with antibiotic irrigation is performed liberally during the procedure, particularly after the use of broaches, reamers, and other processed or autoclaved instruments. Irrigation of soft tissues is done cautiously to avoid the possibility of injection injury from overly aggressive mechanical lavage. Additionally, irrigation of the bone bed prior to implant insertion will help to ensure that no component is placed into an inadvertently contaminated wound. Closure Wound closure is performed in an anatomic fashion by restoring the normal tissue relationships. Debridement of any devitalized tissue within the wound or along the edges of the skin helps to ensure timely healing, a better cosmetic result, and lower risk of infection. Closure starts with repair of the posterior hip capsule and short external rotators. The capsule-tendinous flap can be re-attached through drill holes in the trochanter, or by pulling the flap up underneath the posterior border of the gluteus medius muscle toward the piriformis fossa, pulling the sutures through the gluteus medius tendon, and then tying them over the top of the tendon. The remaining closure is performed in layers that include the fascia overlying the gluteus maximus and tensor fascia, the subcutaneous layer, and the skin. Skin closure can be done with a running

6 410 Part IV B Minimally Invasive Surgery: Total Hip Arthroplasty 53 subcuticular closure, interrupted suture, or staples. The author prefers interrupted suture due to the strength of the interrupted technique, and the more cosmetic appearance of the scar when a modified horizontal mattress suture is used, keeping the side opposite the knot beneath the skin in the subcuticular layer. Important Tips The following tips are of key importance to successfully accomplish total hip arthroplasty through a mini-posterior approach: 1. make the incision long enough to access both the femur and the acetabulum without undue tension on the skin, 2. do not hesitate to lengthen the skin incision during the procedure, 3. protect the soft tissues by moving the extremity and the incision to accommodate the field of view, 4. avoid the prolonged use of tensioned self-retaining retractors, 5. elevate the anterior hip capsule to mobilize the femur and expose the acetabulum, 6. do not let poor mobilization of the femur allow misdirection of the acetabular reamer or acetabular component, 7. do not let poor visualization of the proximal femur result in varus position or undersizing of the femoral component, 8. keep the implants away from the skin edge during insertion. The literature falls short of demonstrating a clear advantage of the minimal posterior hip incision compared to a standard posterior approach or any other minimal incision approach, beyond the cosmetic appeal of a smaller incision. The most comprehensive prospective, and randomized evaluation of the minimal posterior approach compares over 200 hips performed with either an incision less than 10 cm or an incision of 16 cm [19]. The deep dissection performed in the study was the same in both groups. Despite matching patients for age, co-morbidity, and body mass index (BMI), no differences were reported in the rate of transfusion, the assessment of pain, or the use of analgesic medication after surgery. Only the patient s age and preoperative hematocrit correlated with earlier discharge. The length of operation correlated with BMI, independent of the length of the incision. Likewise, early ambulation and optimal component position was not impacted by the length of the skin incision. While this study was very well designed and executed, one could argue that the 16 cm incision may not be representative of a standard incision or a more classical posterior approach which often utilized a much longer incision, sometimes including a more extensive and distal deep dissection that might take down the insertion of the gluteus maximus on the posterior femur. Nevertheless, these findings are also reflected in a smaller report of 60 patients comparing an 8 cm incision to a 15 cm incision [20]. While the minimal incision group had less intra-operative blood loss, total blood loss, and fewer limped at 6 weeks, there was no difference in operative time, transfusion rates, narcotic usage, length of stay, rehab milestones, cane usage, or rates of complications out to 2 years post-operatively. Results While the literature on the results of all minimally invasive approaches remains quite limited, the available reports on the mini-posterior approach for total hip arthroplasty are the most numerous. The literature consists of a number of single surgeon case series, a few comparative studies, and fewer prospective evaluations. Most evaluations are short term, therefore not addressing the impact of the less invasive approach on the long term performance of the total hip procedure. The case series available in the literature serve to demonstrate that a total hip can be done safely through a minimal posterior hip incision in the hands of an experienced surgeon [17, 18]. Complications Particularly important is the consideration of potential complications or unique hazards that might be introduced by the minimal incision approach. Several case reports have outlined the potential for improper reaming of the acetabulum, vertical cup placement, intra-operative fractures, and prolonged operative time, citing surgeon inexperience as a possible cause [21]. While those complications are not unique to the minimal incision approach, at least one study has suggested that the minimal posterior incision might be associated with a higher rate of complications than a standard approach [22]. In a comparison of a group of patients with a standard posterior approach

7 Chapter 53 Posterior Minimally Invasive Surgery Approach for Total Hip Arthroplasty to a group with a minimal incision posterior approach, the minimal incision group had a higher incidence of wound complications and component mal-position. This finding was remarkable in light of the fact that the minimal incision group had a lower mean BMI. Finally, recent evidence has pointed to the fact that all minimal incision approaches for THA cause some damage to muscle. A dissection of 20 cadaver hip replacement procedures, divided between 10 mini-posterior approaches and 10 2-incision approaches revealed more damage to the gluteus medius and minimus muscle after the 2-incision technique, but no difference in damage to the gluteus tendon between the two groups [23]. Discussion and Conclusions The minimal incision posterior approach for total hip arthroplasty represents an evolution of the standard posterior incision, focusing the exposure only on the pertinent anatomy required to perform a total hip replacement successfully. The minimal posterior approach can result in a highly functional early recovery and a cosmetic result, but it also has the potential to add complexity to the total hip replacement procedure. Success is linked to experience and meticulous soft-tissue management. References 1. Roberts JM, Fu FH, McCain EF, Ferguson AB (1984) A comparison of posterolateral and anterolateral approaches to total hip arthroplasty. Clin Orthop 187: Joshi A, Lee CM, Markovic L, Vlatis G, Murphy JCM (1998) Prognosis of dislocation after total hip arthroplasty. J Arthroplasty 13: Kennon R, Keggi J, Zatorski L, Keggi K (2004) Anterior approach for total hip arthroplasty beyond the minimally invasive technique. J Bone Joint Surg 86A (Suppl 2): Light T, Keggi K (1980) Anterior approach to hip arthroplasty. Clin Orthop 152: Hardinge K (1982) The direct lateral approach to the hip. J Bone Joint Surg 64B: Lu-Yao GL, Keller RB, Littenberg B, Wennberg JE (1994) Outcomes after displaced fractures of the femoral neck: A meta-analysis of one hundred and six published reports. J Bone Joint Surg 76A: Woolson ST, Rahimtoola ZO (1999) Risk factors for dislocation during the first 3 months after primary total hip replacement. J Arthroplasty 14: Pellicci PM, Bostrom M, Poss R (1998) Posterior approach to total hip replacement using enhanced posterior soft tissue repair. Clin Orthop 355: Moore AT (1957) The self locking metal hip prosthesis. J Bone Joint Surg 39A: Vail TP (2004) Minimal Incision hip arthroplasty the posterior mini-incision. Semin Arthroplasty 15(2): Sculco T (2003) Is smaller necessarily better? Am J Orthopedics 32: Berry D, Berger R, Callaghan J et al. (2003) Minimally invasive total hip arthroplasty development, early results and a critical analysis. J Bone Joint Surg 85A(11): McCollum DE, Gray WJ (1990) Dislocation after total hip arthroplasty. Causes and prevention. Clin Orthop 261: Johanson NA, Pellicci PM, Tsairis P, Salvati EA (1983) Nerve injury in total hip arthroplasty. Clin Orthop 179: Murphy SB (2004) Technique of tissue-preserving minimally-invasive total hip arthroplasty using a superior capsulotomy. Oper Tech Orthop 12: Hewitt JD, Glisson RR, Guilak F, Vail TP (2002) The mechanical properties of the human hip capsule ligaments. J Arthroplasty 17(1): Goldstein W, Branson J, Berland K, Gordon A (2003) Minimal-incision total hip arthroplasty. J Bone Joint Surg 85A: Swanson T (2005) Early results of 1000 consecutive, posterior, single-incision minimally invasive surgery total hip arthroplasties. J Arthroplasty 20 (Suppl): Ogonda L, Wilson R, Archbold P et al. (2005) A minimal-incision technique in total hip arthroplasty does not improve early postoperative outcomes a prospective, randomized, controlled trial. J Bone Joint Surg 87A(4): Chimento G, Pavone V, Sharrock N et al. (2005) Minimally invasive total hip arthroplasty a prospective randomized study. J Arthroplasty 20: Fehring T, Mason J (2005) Catastrophic complications of minimally invasive hip surgery. J Bone Joint Surg 87A: Woolson ST, Mow C, Syquia J et al. (2004) Comparison of primary total hip replacements performed with standard incision or a mini-incision. J Bone Joint Surg 86A(7): Mardones R, Pagnano M, Nemanich J, Trousdale R (2005) Muscle damage after total hip arthroplasty done with the two-incision and mini-posterior techniques. Clin Orthop 441: 63 67