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The posterior approach provides access to the superior rim of the acetabulum, the posterior column, contained defects within the acetabulum, and the entire femur.
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The posterior approach is not ideal for large superior and anterior column defects.
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The sciatic nerve and the superior gluteal nerve are the key structures at risk with the posterior approach.
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A methodical release of soft-tissue attachments around the proximal femur allows mobilization and circumferential visualization.
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Posterior hip precautions are necessary to minimize the risk of postoperative dislocation.
The posterior approach to the hip is a versatile and extensile approach that can be used effectively for the majority of hip revision procedures. The incision is typically curvilinear, extending from the posterior superior iliac spine (PSIS) toward the tip of the greater trochanter, and then extending distally along the shaft of the femur as far as required to meet the goals of the operation. The distal extension is determined by factors such as the need to remove an existing stem, locate a cortical defect or fracture, perform an osteotomy, or apply a bone graft.
INDICATIONS AND CONTRAINDICATIONS
The posterior approach is indicated when access to the femur is a primary requirement for reconstruction. The posterior approach can provide visualization of the entire lateral and anterior femoral cortex distally, as well as the proximal femoral cortex and femoral canal. Likewise, the posterior approach is appropriate for wide acetabular exposure that can also expose the posterior column and superior rim defects that do not extend far into the quadrilateral surface of the pelvis or into the anterior column. The posterior column is accessible for most indications, including plating, hardware removal, sciatic nerve visualization, placement of a jumbo spherical cup or acetabular cage, and bone grafting.
The limitations of and contraindications to the posterior approach are primarily based on the lack of access to the anterior column and the quadrilateral surface of the pelvis or on the need to avoid operating through the posterior capsule of the hip joint. The proximal extension of the posterior approach is limited by the lack of excursion of the superior gluteal neurovascular pedicle emerging from the sciatic notch and supplying the gluteus medius muscle. This pedicle cannot be stretched sufficiently to allow a wide exposure of the lateral wall of the pelvis without risking denervation of the gluteus medius and tensor fascia lata muscles. When the integrity of the posterior hip capsule is of primary importance because of considerations of joint stability, the posterior approach is not the approach of choice owing to the risk of posterior hip dislocation.
PREOPERATIVE PLANNING
Preoperative planning starts with determining whether the posterior approach will afford access to that part of the pelvis and femur critical to meet the reconstructive goals. The posterior approach will allow access to the superior rim of the acetabulum, the acetabulum itself, contained anterior column defects, any type of posterior column defect, and virtually the entire femur. The posterior approach is not ideal for large superior or anterior pelvic or anterior column defects. With that anatomic footprint in mind, careful imaging will allow a determination of whether the posterior approach is the right choice in a given situation.
Other preoperative considerations include prior incisions and procedures, a history of posterior instability, or retained hardware. Although the posterior approach can be used after any prior approach, it is advisable to use prior incisions or approaches when there is no advantage to using the posterior approach. Examples might include the prior use of an anterior approach or an anterolateral approach for liner exchange, débridement, or isolated acetabular revision (particularly with a history of posterior instability).
Once it has been determined that the posterior approach is appropriate with regard to skeletal access, further consideration should be given to the length of the incision required and the exact placement of the incision. Procedures that require a more extensive exposure of the posterior column can be facilitated by placing the incision more posteriorly. Situations in which a trochanteric osteotomy is contemplated might be better served by a straighter, more trochanteric-based incision. A more distal extension of the approach provides access to the femoral shaft when required.
TECHNIQUE
After the surgical site is marked, the patient is positioned in the lateral decubitus position. All downside pressure points should be padded, with particular attention paid to the peroneal nerve just below the fibular head on the downside leg. An axillary roll under the thorax provides protection to the downside shoulder and the brachial plexus. For procedures that are anticipated to take longer or that may be associated with larger volumes of blood loss because of an extended exposure, appropriate monitoring of fluid status with central pressure, a urinary catheter, and use of an intraoperative blood salvage device should be considered. The leg is draped free with the foot isolated by an impervious drape so that the leg can be manipulated during surgery. Adhesive drapes obviate the need for wound towels and can isolate any exposed skin surface, which is a potential source of contamination if exposed during the procedure.
Planning the skin incision entails the use of surface landmarks such as the PSIS, the sciatic notch, the tip of the greater trochanter, and the femoral shaft. The incision will be centered over the greater trochanter, with the proximal limb extending toward the PSIS, and the distal limb paralleling the femoral shaft ( Fig. 34-1 ). The skin is incised with a knife, and the initial dissection is carried through the subcutaneous fat down to the tensor fascia. The fascia may be exposed by carefully elevating the fat just enough to expose the edges of the fascia for later closure. The fat and skin should be handled with care throughout the surgery to prevent devascularization or injury that could predispose to wound dehiscence or breakdown of the skin closure.
The deep dissection passes through the gluteus maximus (innervation—inferior gluteal nerve), posterior to the gluteus medius muscle (innervation—superior gluteal nerve) and gluteus minimus muscle (innervation—superior gluteal nerve), and through the insertion of the piriformis muscle, the superior gemellus, the obturator internus, the inferior gemellus, the obturator externus, and the quadratus femoris muscle in that order from proximal to distal (innervation—sacral plexus, L5, S1, S2).
The deep dissection is started by dividing the tensor fascia overlying the vastus lateralis distally. The exposure is facilitated by starting distal to any prior incision where a defined tissue plane exists between the tensor and the underlying vastus lateralis. Starting distal to a prior scar ensures that the appropriate interval is established within tissue planes that have not been disrupted by granuloma formation or scar adhesions. The exposure is extended proximally into the gluteus maximus muscle at the posterior third of the muscle body. Once the distal portion of the fascial incision is made through the tensor fascia, it is possible to palpate cephalad onto the undersurface of the gluteus maximus muscle to locate the primary raphe of its pennate structure. The muscle is then divided bluntly and slowly, with attention paid to coagulation of bleeding points during the muscle separation. The gluteus maximus is divided longitudinally between its fibers toward the PSIS, with separation of enough muscle to allow palpation of the sciatic notch at the proximal extent of the exposure. Once the muscle is divided, a retractor can be placed into the wound below the muscle to retract the skin, the subcutaneous fat, and the gluteus maximus muscle. Self-retaining retractors should be placed with the minimum pressure required for exposure at the wound edges, and they should be released frequently to avoid pressure damage to the retracted structures.
Palpate and protect the sciatic nerve during the approach. Know where the nerve is traveling throughout the surgery. The sciatic nerve is particularly vulnerable to indirect stretch injury from retractors, or direct injury during the approach. In a revision procedure, the nerve may be encased in scar and it may be flattened to the point that it is difficult to distinguish the nerve from other soft tissues. The sciatic nerve is particularly at risk when an operation is carried out through a previous posterior exposure and when there are posterior column bone defects, posterior column internal fixation, or large amounts of heterotopic bone present in the vicinity of the nerve. In order for its location to be clearly determined, the nerve can be found at several predictable anatomic points: as it exits from the sciatic notch, lying superficial to the ischial tuberosity, or distally under the gluteus maximus tendon insertion at the linea aspera of the femur. To ensure the safety of the sciatic nerve when its course cannot be ensured by palpation or visualization, find it distally and track it proximally. Keeping the patient’s knee bent during the procedure is a way to relieve pressure from the nerve associated with stretching. Routine exposure or neurolysis is not required if the nerve can be palpated or visualized and protected.
Once the posterior border of the gluteus medius muscle is exposed, the joint itself can be entered through the hip capsule. The capsulotomy proceeds from the acetabular rim along the posterior border of the gluteus medius (or the superior border of the piriformis when it is present). The exposure is facilitated by gently elevating the gluteus medius muscle and tendon to create a separation between the undersurface of the medius and superficial surface of the minimus muscle. If that interval can be established, then a retractor (typically a blunt Hohmann retractor) can be placed over the gluteus minimus and onto the anterior hip capsule. The posterior edge of the gluteus medius is gently retracted forward with the retractor. One can then make the capsulotomy along the cephalad border of the piriformis, proceeding distally from the acetabular rim, behind the gluteus medius and minimus muscles, ending the proximal limb of the capsulotomy near the piriformis fossa. The standard capsulotomy is fashioned in an L shape ( Fig. 34-2 ), with the apex at the piriformis fossa, and the distal limb continuing across the insertion of the piriformis tendon and the conjoint tendon (obturator and gemellus muscles). When possible, it is advisable to separate and tag the short external rotators, including the piriformis, conjoint tendon, and posterior hip capsule, to facilitate later repair. However, in many revision procedures these structures are scarred together and cannot be individually identified. The posterior capsule may be scarred or absent in patients with a history of granulomatous inflammation resulting from wear debris or recurrent dislocation. In most revisions the dissection will need to be extended distally in order to properly expose the femur. The distal release may include not only the short external rotators but also the iliopsoas tendon insertion on the lesser trochanter, and the gluteus maximus muscle insertion on the posterior femur. The more distal dissection facilitates the elevation of the femur from the wound, dislocation of the femoral head, and internal rotation of the femur.
