The most accepted indication for acetabular reorientation is mild to moderate symptomatic hip dysplasia (Figure 41.1). Initially, there was controversy about the degree of dysplasia and concomitant femoral head deformity that can be adequately addressed with a PAO; it was felt that severely subluxed hips would not be candidates for a PAO. Subsequently, good outcomes have been published for more severe deformities, and the indications have been expanded as long as a concentric hip joint is possible. Thus, dysplasia secondary to Legg-Calvé-Perthes disease and dysplasia secondary to flaccid and spastic neuromuscular disorders can be considered appropriate indications for PAO. Global acetabular retroversion causing impingement is also considered an indication for PAO, particularly if the retroversion is associated with posterior wall deficiency or posterior instability.

There may also be a role for acetabular reorientation in patients with borderline dysplasia (center edge angle of 20°–25°) and clinically symptomatic instability. This occurs most often in the setting of increased femoral and/or acetabular anteversion, and primarily manifests as iliopsoas or abductor fatigue symptoms.

Mid- and long-term follow-up have established that the most predictable outcomes are in patients less than 35 years
old at the time of surgery with little to no arthritis (Tönnis Grade 0 or 1) on plain radiographs. Good results have, however, been reported for patients over 35 or 40, even in early series, with the caveat that there is minimal arthrosis and the hip is concentric on preoperative imaging.

Study results of PAO in patients with preoperative arthrosis reveal that Tönnis Grades 2 and 3 are greater predictors of failure. Although the presence of Tönnis Grade 2 or 3 arthrosis is a predictor of failure, some patients with this degree of arthrosis show improved outcomes scores and relatively preserved joint space in midterm follow-up. Thus, although arthrosis is a relative contraindication to PAO, PAO may be preferable to total hip arthroplasty in certain younger patients.

Contraindications to PAO include incongruence on functional radiographs (abduction and internal rotation images or flexion false profile images), which indicates potentially worse congruency after acetabular reorientation and is thus a predictor of worse outcomes. This can occur in nonspherical femoral heads or when the acetabular radius is smaller than the femoral head radius. PAO is also contraindicated in very young patients (less than 10 or 11 years of age) because of the risk of injury to the triradiate cartilage.

The PAO can be performed with adjuvant arthroscopy, which is performed for labral repair or débridement and cartilage assessment; the arthroscopy is performed first with the patient on a traction table using a standard technique. Most patients with hip dysplasia also have some form of intra-articular pathology and labral injury; concurrent hip arthroscopy allows intra-articular injury to be addressed concomitant with the PAO. The combination of arthroscopy and PAO in the same setting has been previously described, but outcomes data are not yet available.

For the PAO, the incision is slightly curved lateral to the anterior superior iliac spine (ASIS) and the tensor-sartorius interval. The ASIS is osteotomized and reflected medially, preserving the sartorius attachment on the osteotomized fragment. Care is taken near the ASIS because the lateral femoral cutaneous nerve emerges proximally within 5 cm of and medial to the ASIS, and can be injured during the approach. Proximally, the external oblique aponeurosis is sharply incised and the iliacus is elevated subperiosteally and medially off the iliac wing. Because of reports of prolonged hip flexor weakness after PAO, the direct and indirect head of the rectus can be left attached (rectus-sparing modification) and retracted laterally during the capsular exposure. A retractor is placed deep to the iliopsoas tendon to allow retraction of the tendon. Once the lateral aspect of the superior pubic ramus is visualized, the subperiosteal dissection of the ilium can be extended to the quadrilateral plate. This allows a blunt Hohman to be placed on the ischial spine near the sciatic nerve, and enables visualization of the inner table of the pelvis. EMG studies indicate that nerve irritation does occur intraoperatively; thus, it is critical that care be taken with retractor placement.

The interval between the iliopsoas tendon and the joint capsule is developed medially, allowing access to the ischium for the first osteotomy. A specially curved or angled chisel is then passed into the interval and used to make the first cut (Figure 41.2). The osteotomy is performed using fluoroscopic visualization and begins just inferior to the infracotyloid notch, extending posteriorly towards the base of the ischial spine (Figure 41.3). The lateral portion of the ischial osteotomy is very close to the sciatic nerve; the nerve is at risk if the osteotome slips laterally. The nerve can be protected to a certain extent by placing the leg in abduction and knee flexion, and directing the osteotome medially.

Attention is then directed to the pubic osteotomy. The superior pubic ramus is dissected subperiosteally. Blunt retractors are placed around the bone to protect the obturator nerve, which runs on the inferior aspect of the ramus. The cut is made just medial to the iliopectineal eminence and perpendicular to the bone, which is generally about 45° to the plane of the table. This osteotomy is deep to the retracted Iliopsoas tendon; therefore, the iliopsoas will be weak in the postoperative period.

Attention is turned to the supra-acetabular osteotomy. The abductors are tunneled only at the level of the osteotomy, and a blunt Hohman retractor is placed laterally near the greater sciatic notch. Additional soft tissue is elevated off the quadrilateral surface. There are two portions to the supra-acetabular cuts; the first passes through the iliac wing and the second is retroacetabular, meeting up with the ischial osteotomy. Both are often performed under direct and fluoroscopic visualization, and can be made with either an oscillating saw or osteotome. The retroacetabular cut angles 120° from the supra-acetabular cut and is directed toward the first ischial cut (Figure 41.4).

Depending on the patient’s anatomy, the retroacetabular osteotomy is performed with either a straight or curved osteotome. This extends along the posterior column to meet the ischial osteotomy. The cut should be just posterior to the midpoint of the width of the posterior column, defined as the area between the hip joint and the sciatic notch. The osteotome is angled slightly from anterior to posterior to avoid the posterior part of the joint (Figure 41.5). A useful fluoroscopic technique is to see a perfect lateral image of the osteotome on false profile view when beginning the osteotomy. Once the osteotomy is completed medially, the lateral cortex is osteotomized as a controlled fracture. This is undertaken to protect the sciatic nerve, which is directly inferior to the lateral cortex and would be at risk if the osteotomes were used to complete the lateral osteotomy. Fluoroscopy is used to ensure that the retroacetabular osteotomy meets the ischial osteotomy. Once the medial aspects of the osteotomy are performed, the posterolatereral cortex where the iliac and the posterior column osteotomies meet can be cut with an angled osteotome, which also allows more fragment mobilization (Figure 41.5).
At this point, there is some risk of the osteotomy propagating into the sciatic notch, with subsequent discontinuity of the posterior column. Although this may ultimately be of little consequence, it does compromise the stability of the healing fragment; thus, the patient must remain non–weight-bearing until evidence of fragment healing is seen.

When all of the cuts have been made, a Schanz pin is placed in the acetabular fragment at the anterior inferior iliac spine (AIIS), angled posterior between the inner and outer tables of the pelvis. This facilitates fragment mobilization and control of the fragment during correction. At this time, the fragment should move freely (Figure 41.6). This is important because, if it does not, the soft tissue or bony hinging hinders the correction and limits medialization of the joint. For “classic dysplasia,” lateral and anterior correction is essential; thus, the fragment should be adducted and flexed. Nonetheless, the correction should be individualized for each patient and based on the anatomy and information from the preoperative radiographs. Once a preliminary correction has been obtained, the fragment is fixed with 2.4-mm Kirschner wires (K-wires) and evaluated fluoroscopically. There are five parameters to assess intraoperatively:

Once a satisfactory correction has been obtained, 3.5-mm or 4.5-mm cortical screws can be placed for definitive fixation (Figure 41.7).

Once the correction is obtained and stable, any potential impingement is addressed. Hip range of motion (ROM) in flexion and internal and external rotation are evaluated. An anterior capsulotomy to evaluate for impingement is routinely performed to evaluate any potential impingement. Depending on the proximal femoral anatomy, a femoral neck osteoplasty can be performed, particularly if there are any limits to motion. In addition, any restrictions in motion or impingement from the AIIS can be assessed and bone from the AIIS can be resected if it is causing impingement. The capsule is then repaired with absorbable suture. The ASIS osteotomy is fixed with a 3.5-mm cortical screw and the remainder of the wound is closed in a layered fashion.

Postoperatively, patients remain in the hospital for 3 to 6 days for pain control and mobilization. Weight bearing is limited to 20% the first 4 to 6 weeks because load-to-failure testing of the screw constructs found that ultimate failure can occur with loads as low as 1.27 times body weight. In addition, loss of correction and stress fractures of the intact pelvis have occurred in patients who began weight bearing too soon after surgery. Aspirin is used for routine thrombosis prophylaxis. The overall incidence of venous thrombosis following PAO is low (0.94%). In otherwise low-risk patients, the complications
of enoxaparin (Lovenox) or other chemoprophylaxis include prolonged wound drainage, hematoma, and bleeding, which largely outweigh the risk of deep vein thrombosis (DVT) or pulmonary embolus.

Postoperatively, patients remain in the hospital for 3 to 6 days for pain control and mobilization. The primary goal of this phase is healing and pain control. Patient education emphasizes protection of the surgical site and compliance with activity modification to minimize pain and inflammation. Weight bearing (WB) is limited to 20% of body weight to protect the healing osteotomy (Figure 41.8). It is important to note that non-weight bearing (NWB) should be avoided, as this will place undue stress on the hip flexors, which will be working to hold the lower extremity from contacting the floor—this action will result in pain. Patients are encouraged to ambulate with a foot flat progression to establish a more natural walking pattern. Home exercise instruction focuses on isometric contraction and establishment of core stability.