Single-incision piriformis-sparing posterior THA approach does not require special instruments

Issue: April 2018

ByGeert Meermans, MD

Total hip arthroplasty is one of the most successful surgical procedures for relieving pain and improving quality of life and has been called “the operation of the century.” Despite this success, early and late complications have been reported and dislocation remains one of the most common early complications after THA. The causes of dislocation are multifactorial and can be attributed to patient characteristics, surgical technique and component positioning. Historically, the posterior approach has been associated with a higher risk of dislocation compared with a lateral or anterolateral approach. It is still favored by most surgeons because of its excellent exposure of both the acetabulum and femur and the fact that a standard posterior approach can be easily extended in difficult cases or when intraoperative complications, such as fractures, occur.

The increased risk of dislocation using a posterior approach is attributed to disruption of the posterior soft tissue structures, including the short external rotators of the hip and the posterior capsule. Adequate soft tissue repair greatly reduces the relative risk of dislocation using a posterior approach. In addition, there have been continued efforts in the past decade to modify the posterior approach to help preserve the posterior soft tissues without compromising exposure and implant positioning.

This article reviews the surgical technique of a modified posterior approach through a single incision without the need for specially designed instruments and with preservation of the piriformis tendon insertion at the greater trochanter (GT).

Patient positioning

Patients are positioned in the lateral decubitus position using lumbar and pubic supports. Preoperatively, the pubic symphysis and both anterior superior iliac spines are used to assess pelvic tilt and rotation. Both hips are flexed approximately 45° and the tip, anterior, and posterior borders of the GT are marked. The borders of the incision are marked 4-cm proximal and 8-cm distal from the tip of the GT (Figure 1). With added experience and in slim patients, the incision can be made smaller.

Approach

A slightly proximal posterior-curved incision is made which runs through the posterior third at the level of the GT. Sharp dissection is done through the subcutis. The gluteus maximus is split in the line of its fibers and the fascia lata is split distally in the line of the incision. The soft tissues are retracted with a self-retaining retractor. The sciatic nerve is palpated to check its location and proximity to the posterior structures. The leg is internally rotated by an assistant or by placing the ipsilateral foot on the edge of an elevated surgical instrument table with a sterile padding or gauze to prevent compressive lesions.

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A pointed Hohmann retractor is placed under the posterior edge of the gluteus medius and proximal of the piriformis tendon, which can be easily identified visually or by palpation. To facilitate discrimination of the different anatomical landmarks, the fascial layer covering the piriformis, obturator internus and gemelli can be removed by making a superficial, horizontal incision posterior to the GT and sweeping it posterior using a gauze. By retracting the Hohmann anterior and superior, the posterior structures are exposed (Figure 2). There are several small vessels covering the tendons and muscles that should be coagulated using a diathermy. The capsule is incised along the inferior border of the piriformis tendon from the edge of the acetabulum to the posterior border of the femur. The incision is continued distally along the intertrochanteric crest. To remove the capsule as close to its bony insertion as possible, the blade electrode of the diathermy can be bent to facilitate capsular release around the intertrochanteric crest. Two Vicryl 2-stay sutures are placed in the capsule and external rotators. The first one is placed in the corner of the vertical and horizontal limb of the capsule and the second one is placed 3-cm more distal. A third stay suture is placed through the non-detached posterosuperior capsule at the insertion of the piriformis tendon at the GT (Figure 3).

Posterior THA approach — **Figure 1.** The patient is placed in lateral decubitus position. The dotted lines represent the outline of the GT. The full lines mark the proximal and distal edge of the incision.

Femoral osteotomy

At this point, the hip can be dislocated by internal rotation and flexion of the femur. The proper level of the osteotomy can be determined based on preoperative planning in reference to the tip of the GT, the superior border of the lesser trochanter or by placing a trial femoral broach parallel to the femur and aligning the center of rotation of the native femoral head and trial head (Figure 4). When necessary, the quadratus femoris may be partially detached to improve exposure. A Hohmann retractor is placed on the medial border of the femoral neck to protect the soft tissues when using an oscillating saw for the osteotomy.

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Exposure of the acetabulum

After removal of the femoral head, a Hohmann retractor is placed over the anterior and superior wall of the acetabulum to retract the proximal femur anteriorly. Exposure can be improved by flexing the ipsilateral hip, which relaxes the anterior capsule and allows more anterior retraction of the femur. When tight, the anterior capsule may need to be released. The acetabulum is further exposed using a Charnley pin posteriorly between the released capsule and the posterior acetabular wall. The inferior capsule is incised using electrocautery, and a double-prong retractor is placed inferiorly to improve exposure of the transverse acetabular ligament (TAL) and facilitate entry of the acetabular reamers. When deemed necessary, an additional Charnley pin is placed superiorly to get a full 360°-exposure of the acetabulum (Figure 5).

Exposure of the femur

The proximal femur is presented by flexion, adduction and internal rotation of the hip. A proximal femoral elevator is used to improve exposure. This elevator can be attached to a chain with a clamp (Figure 6). A Hohmann retractor is placed laterally to protect the soft tissues and prevent skin abrasion. An extra retractor can be placed medially in the event soft tissue produces a suboptimal view of the proximal femur (Figure 7). The femoral canal is opened and prepared with standard broaches.

Capsular reattachment

The capsule and external rotators are reattached to the bone using a posterior transosseous repair. Two drill holes are made in the GT, the first superiorly in the middle-third adjacent to the insertion of the piriformis tendon that can be palpated. The second drill hole is made at the posterior edge of the GT and exits anterior of the intertrochanteric crest. The two stay sutures of the detached capsule are passed through the holes. The stay suture of the non-detached posterosuperior capsule is passed through the corner of the detached capsule to allow closure of the vertical limb of the capsule release (Figure 8). The sutures passed through the drill holes are tied first with the hip in slight flexion and neutral rotation. A Hohmann retractor is placed under the posterior edge of the gluteus medius and proximal of the piriformis tendon. The vertical limb of the capsular release is sutured side-to-side (Figure 9).

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Proximal femur presentation and suturing — **Figure 6.** Presentation of the proximal femur by flexion and adduction internal rotation of the hip is shown. A femoral elevator is attached to a chain.

Key points

Place the incision along the posterior third of the GT. In this way the posterior structures are in direct line with the skin incision and a more extensile approach can be avoided.
Detach the capsule as close to its bony insertion as possible. This can be difficult because of the intertrochanteric crest. Bending a diathermy blade allows working around the corner.
Flex the femur for better anterior exposure of the acetabulum. This will relax the anterior capsule and allow more anterior translation of the proximal femur.
Use a femoral elevator to improve vision and access to the proximal femur. Attaching this elevator with a clamp to a chain avoids the use of an extra hand.
Reattach the capsule to its anatomic position by placing the drillholes in the correct position. The ideal exit point of the proximal hole is directly inferior of the non-detached capsule. For the distal hole this is anteriorly of the intertrochanteric crest.
Close the vertical limb of the capsular release by placing a stay suture in the non-detached capsule at the insertion of the piriformis tendon at the GT. Place this suture through the corner of the detached capsule before tying the transosseous capsular sutures.

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For more information:
Geert Meermans, MD, can be reached at Department of Orthopaedics - Bravis Hospital, Boerhaavelaan 25, 4708 AE Roosendaal, the Netherlands; email: geertmeermans@hotmail.com.

Disclosure: Meermans reports he receives institutional support from DePuy Synthes, a Johnson & Johnson company, and Zimmer Biomet; and receives consulting fees from DePuy Synthes, a Johnson & Johnson company.