Posterior Approach to the Acetabulum

The posterior approach gives access to the posterior wall of the acetabulum and its posterior column (Fig. 7-39). It also allows direct visualization of the dorsocranial part of the acetabulum, either through the fracture gap or via a capsulotomy. It is by far the easiest of all acetabular approaches, and extensive blood loss is not usually encountered. The approach also allows access to the anterior column if a trochanteric osteotomy and surgical dislocation of the hip is performed.7,8

Its uses include reduction and fixation of:

1. Fractures of the posterior lip of the acetabulum

2. Fractures of the posterior column

3. Fractures of the posterior lip and posterior column

4. (Juxta- and infratectal) Simple transverse fractures

5. Transverse fractures with associated posterior lip fractures

If a trochanteric osteotomy and surgical dislocation of the hip is used, it can also be used for anterior lip fractures, dome fractures, and acetabular fractures in association with femoral head fractures.

Position of the Patient

Two positions are possible. If the approach is to be used for fractures of the posterior lip and/or posterior column, place the patient in the lateral position. This position is also used if a trochanteric osteotomy is planned.

Alternatively, if the approach is to be used for transverse fractures, place the patient in the prone position (Fig. 7-40). If traction is to be used, place a skeletal pin transversely through the lower end of the femur with the knee flexed to reduce the risk of a traction injury to the sciatic nerve.

Figure 7-39 The posterior approach to the acetabulum allows access to the posterior column, posterior lip, and dome segment of the acetabulum.

With the patient in the lateral position, there is a natural tendency for the femoral head to move medially in cases of transverse acetabular fracture. Operating in the lateral position, therefore, makes reduction of these fractures more difficult. Reduction of the fracture in this position can only be obtained by an assistant lifting the femoral head out of the acetabulum. The use of the prone position facilitates reduction of transverse fractures.

Landmarks and Incision

Landmarks

Palpate the greater trochanter on the outer aspect of the thigh. Note that the posterior edge is easier to palpate than the anterior one.

Incision

Make a longitudinal incision centered on the greater trochanter extending from just below the iliac crest to 10 cm below the tip of the greater trochanter (Fig. 7-41).

Internervous Plane

There is no true internervous plane in this approach. However, the gluteus maximus that is split in the line of its fibers is not significantly denervated because it receives its nerve supply well proximal to the split.

Superficial Surgical Dissection

Deepen the incision through subcutaneous fat. Incise the fascia lata in the line of the skin incision in the lower half of the wound, and extend this incision superiorly along the anterior border of the gluteus maximus muscles (Fig. 7-42). Retract the split edges of the fascia to reveal the piriformis muscle and the short external rotators of the hip (Fig. 7-43). Partial detachment of the insertion of gluteus maximus from the femur will facilitate mobilization of this muscle.

Figure 7-40 Position of the patient for posterior approach to the acetabulum. Position of the patient for posterior approach to the acetabulum if a trochanteric flip osteotomy is not to be used. Note the flexed position of the knee to prevent stretching of the sciatic nerve.

Figure 7-41 Make a longitudinal incision centered on the greater trochanter extending from just below the iliac crest to 10 cm below the greater trochanter.

Figure 7-42 Incise the fascia lata in line with the skin incision. Extend the incision superiorly along the anterior border of the gluteus maximus muscle.

Figure 7-43 Retract the split edges of the fascia to reveal the piriformis muscle and the short external rotators of the hip.

Deep Surgical Dissection

Internally rotate the leg to put the short external rotators and the piriformis on the stretch. Identify the quadratus femoris muscle and superior to this the tendon of obturator internus with the accompanying gemelli muscles. Finally identify the piriformis muscle and tendon lying above the superior gemellus. Palpate the sciatic nerve as it runs down the leg lying on the short external rotator muscles and trace the nerve proximally. It usually passes anterior to the piriformis muscle to enter the greater sciatic notch. Detach the tendon of obturator internus and the two gemelli muscles as they insert into the femur (Fig. 7-44). If the sciatic nerve is bifid and you wish to perform a surgical dislocation of the hip, then also divide the

tendon of the piriformis muscle to prevent a traction lesion of the nerve. Using the short external rotator muscles as a cushion, carefully insert a retractor into the greater sciatic notch. Do not apply great pressure on this retractor as this will create a sciatic nerve palsy. Insert a second retractor into the lesser sciatic notch to expose the posterior column in its whole extent.

The posterior capsule of the hip is revealed. This is often torn or detached in cases of trauma. If the posterior capsule is intact and a direct inspection of the joint is required, make a T-shaped capsulotomy. Ensure that you avoid damage to the limbus when incising the capsule.

The inner surface of the acetabulum can only be viewed by distracting the femoral head. This can either be achieved by skeletal traction or with the help of a Schanz screw placed in the femoral head.

Posterior lip fractures of the acetabulum can be adequately visualized and fixed at this stage. If you require more extensive exposure of the posterior column, as, for example, a posterosuperior wall fracture, a transverse fracture with an associated posterior wall fracture or a T-shaped fracture perform an osteotomy of the greater trochanter. If the piriformis tendon is still attached to the greater trochanter develop a plane between the piriformis muscle inferiorly and the gluteus medius superiorly. Continue this dissection to the greater sciatic notch. Deep to the gluteus medius identify the gluteus minimus muscle and develop a plane between this muscle and the piriformis. Take care not to injure branches of the superior gluteal nerves and vessels which run in this intermuscular interval. Mark the bone from the tip of the trochanter to the vastus tubercle using cutting diathermy and then divide the greater trochanter from posterior to anterior, removing a piece of bone 5 mm in size. Creating a step osteotomy (Fig. 7-45) gives the osteotomized bone stability when it is reattached to the femur.

Figure 7-44 Divide the short external rotator muscles 1 cm from their insertion into the femur.

This bone will have the gluteal muscles and possibly the piriformis muscle attached to it superiorly and the vastus lateralis attached to it inferiorly. Divide the fascia overlying the vastus lateralis muscle for about 5 cm distal to the vastus tubercle to increase the mobility of the muscle. Then progressively evert the trochanter with its attached muscles over the anterior surface of the femur using a sharp retractor (Fig. 7-46). The small remaining attachment of gluteus medius to the intertrochanteric ridge will now need to be released. If difficulty is encountered mobilizing the fragment, the insertion of piriformis may sometimes need to be partially released if this has not already been done.

If you require access to the anterior surface of the hip joint capsule, flex and externally rotate the hip. Mobilize the insertion of gluteus minimus from the retroacetabular surface along the superior capsule to its femoral insertion along the anterior aspect of the trochanter. If further

exposure of the anterior structure is required, perform a Z-shaped capsulotomy to inspect the inside of the joint (Figs. 7-47 and 7-48). Apply traction to the limb to partially sublux the joint and allow visualization of the ligamentum teres. Divide the ligament and flex the leg to 90 degrees. Adduct the leg and achieve dislocation by applying external rotation. With the femoral head dislocated, appropriate anterior and posterior retraction provides a 360-degree view of the joint and a compete view of the femoral head (Fig. 7-49).

The trochanteric fragment can be reattached easily with screws during closure. Note that trochanteric osteotomies are associated with heterotopic bone formation in acetabular surgery.

Dang

Nerves

The sciatic nerve is often contused by the original trauma. Great care must be taken throughout the operation that the nerve is not forcibly retracted. The divided external rotators will protect the nerve from direct trauma, but the nerve may still be injured by indirect forces transmitted through the retractor. The nerve is in most danger if a fracture table with continuous traction is used. You must be certain that the knee is flexed to avoid stretching the nerve.

Figure 7-45 Create a step osteotomy of the greater trochanter.

If a surgical dislocation of the hip is planned, check that the nerve is not bifid. If it is or if it actually goes through the substance of the piriformis muscle, divide the tendon of the piriformis muscle before fully everting the osteotomized trochanter.

Vessels

The inferior gluteal artery leaves the pelvis beneath the piriformis. This vessel may be damaged by the original fracture or the artery may be injured during the surgical dissection. If the artery is transected, it will retract into the pelvis and bleeding will be brisk. To control the bleeding, apply direct pressure, then turn the patient over into the supine position. If the artery has retracted into the pelvis, vascular control can only be achieved by tying off the external iliac artery via a retroperitoneal

approach.

The superior gluteal artery and nerve leaves the pelvis above the piriformis and enters the deep surface of the gluteus medius. This attachment tethers the muscle, limiting the amount of upward retraction of the muscle and prevents you from reaching the iliac crest. The nerve and artery are at risk if the plane between gluteus minimus and piriformis needs to be developed.

How to Enlarge the Approach

Local Measures

Visualization of the inside of the acetabulum is always difficult because of the presence of an intact femoral head. In addition to using longitudinal femoral traction, specialized femoral head retractors are available that allow the head to be partially dislocated, thereby facilitating clear visualization of the dome of the acetabulum. It is critically important to obtain good visualization of the inside of the joint because the screws used for internal fixation may penetrate the joint.

Extensile Measures

The skin incision can be extended distally down to the level of the knee. Either split the vastus lateralis or elevate it from the lateral intermuscular septum to allow exposure of the lateral surface of the entire shaft of the femur.

The exposure cannot be usefully extended proximally.

Figure 7-46 Progressively evert the trochanter with its attached muscles over the anterior surface of the femur.

Figure 7-47 If further exposure of the anterior structures is required perform a Z-shaped capsulotomy.

Figure 7-48 The femoral head is now revealed.

Figure 7-49 Flex the hip 90 degrees and fully adduct it. Then dislocate the joint by applying an external rotation force. The femoral head then drops posteriorly to reveal a 360-degree view of the acetabulum.