Pelvic Osteotomy Technique for Pincer Impingement

INTRODUCTION

Although the proximal femur is the most common source of femoroacetabular impingement, acetabular morphology can also serve as a source of impingement pathomorphology. Acetabular sources of femoroacetabular impingement usually result from a state of either acetabular retroversion or global acetabular overcoverage (ie, acetabular protrusio). In cases of pathologic version or overcoverage (retroverted or small lunate deep hips), where the lunate cartilage is not amenable to rim reduction, a reorienting periacetabular osteotomy (PAO) is advised to optimize the spatial orientation of the acetabulum.

INDICATIONS FOR SURGERY

The following are the relevant examination and imaging findings of patients with femoroacetabular impingement symptoms who may be considered for a PAO, either anteverting or reverse in nature, to address their abnormal hip mechanics.

Anteverting Periacetabular Osteotomy

Acetabular retroversion is a diagnosis made by clinical examination and imaging analysis. Patients frequently complain of impingement-related difficulties, including pain with sitting and impact activities. There are frequent findings of anterior impingement on examination with pain during flexion and internal rotation of the hip. In severe cases, patients can present with significant limitations to internal rotation and may have findings of obligate external rotation in flexion. Occasionally, patients may also have the sensation of instability during impingement testing, which is the result of the femoral head levering on the anterior acetabular wall, causing subluxation of the femoral head on an insufficient posterior wall.¹

Radiographic findings in these patients include a crossover sign, posterior wall sign, and ischial spine sign on anteroposterior (AP) pelvis radiographs. Frequently, the entire hemipelvis is externally rotated in acetabular retroversion, which explains why a focal acetabular prominence or insufficiency is seldom encountered.² It is imperative that the AP pelvis radiograph be taken with the coccyx overlying the pubic symphysis, as any rotation of the pelvis on this projection will alter the appearance of acetabular version. The AP pelvis should also be scrutinized for the anterior and posterior wall indices, the lateral acetabular coverage (lateral center-edge angle [LCEA], Tönnis angle), and deformity of the proximal femur. Dunn lateral and false profile views should also be obtained to look for femoral cam deformity and anterior acetabular coverage, respectively. Cross-sectional imaging, including both computed tomography (CT) and magnetic resonance imaging (MRI), are essential to accurately quantify the version angle of both the acetabulum and femur and evaluate the articular cartilage and acetabular labrum, respectively.³,⁴

Reverse Periacetabular Osteotomy

Acetabular overcoverage is a diagnosis made by clinical examination and imaging analysis. Patients frequently complain of impingement-related difficulties, including pain with sitting and impact activities. There are frequent findings of anterior impingement on examination with pain during flexion and internal rotation of the hip. In severe cases, patients can present with significant limitations to hip motions including flexion, abduction, and internal rotation.

Radiographic findings in these patients indicate global acetabular overcoverage. AP pelvis radiographs will show elevated lateral acetabular coverage (LCEA >35, Tönnis <0), high anterior and posterior wall indices, and coxa profunda or protrusion. False profile radiographs will similarly show anterior overcoverage. The proximal femur morphology on both AP pelvis and Dunn lateral radiographs should be noted, but cam-type deformity is infrequently encountered in the presence of a truly overcovered
acetabulum.⁵ Cross-sectional studies, specifically CT scans, are beneficial in these patients to accurately identify the bony pathomorphology. CT is particularly helpful by its 3-D reconstructions that help define the size of the lunate cartilage in deep hips. Large lunate hips may be managed with acetabular rim trimming, but small lunate hips are better suited with a reorientation acetabular osteotomy.⁶,⁷

SURGICAL TECHNIQUE

The positioning, approach, and osteotomy technique for both the anteverting and reverse PAO procedures mirror those of the standard PAO for acetabular dysplasia.⁸ An in-depth description of this surgical technique is presented in Chapter 5, but a brief description of this procedure will be. After completion of all osteotomies, the reorientation of the acetabulum for both anteverting and reverse PAOs differ from the traditional PAO and are discussed in greater depth in this chapter.

Positioning and Preparation

Patients undergoing PAO should be placed supine on a radiolucent (ie Jackson) table. Typically, a combination of general anesthesia without motor paralysis and a lumbar plexus block catheter are used. A urinary catheter is placed prior to prep and drape. We typically use a blood collection suction device allowing us an autologous transfusion at the end of surgery.

Approach

A modified Smith-Peterson approach is utilized through a bikini incision to access the hip and pelvis for the periacetabular osteotomies. Briefly, the aponeurosis of the abdominal musculature is elevated from the iliac wing, and the iliac periosteum is sharply divided and elevated medially, giving access to the lateral window of the ilioinguinal approach. Next, the interval between the tensor fascia lata and the sartorius is developed with care to avoid violation of the sartorial compartment in an effort to preserve the lateral femoral cutaneous nerve. This interval is developed proximally to the pelvis, where the sartorius insertion is osteotomized at the anterior superior iliac spine, allowing it to be elevated medially. The distal extent of this interval is typically the ascending branch of the lateral femoral circumflex artery, which should be preserved.

The rectus femoris tendon and iliocapsularis muscle is found at the base of the tensor/sartorius interval. The iliocapsularis is elevated off the rectus tendon and the underlying joint capsule in a lateral to medial direction, with its proximal fibers being released from the anterior inferior iliac spine. As the iliocapsularis is elevated medially, flexion of the hip will facilitate mobilization of both the iliocapsularis muscle and psoas musculotendinous unit. Ultimately, these must be medialized beyond the level of the pubic eminence. The periosteum of the iliac and pubic bones is divided and elevated to the level of the ischial spine medially. Distally, the interval between the hip capsule and the psoas is developed by blunt dissection, allowing access for the first osteotomy cut of the ischium.

Osteotomies

A total of four periacetabular osteotomies are made in order to completely mobilize the acetabular fragment. The typical sequence of osteotomy is the ischial, pubic, iliac, and posterior column. The ischial osteotomy is done under fluoroscopic guidance, using a 30° angled chisel (Ganz osteotome). The goal of this step is an incomplete osteotomy of the ischium (leaving a segment of posterior column bone intact) immediately distal to the hip capsule insertion. This osteotomy will eventually be joined by the posterior column osteotomy.

The pubic osteotomy is made just medial to the pubic eminence and can be made with a variety of tools (Gigli saw, osteotome, burr), but our preference is the Gigli saw. The periosteum of the pubic ramus is elevated both anteriorly and posteriorly around the superior ramus, and retractors are placed to avoid injury to the nearby obturator nerve and vessels. The Gigli saw is passed from anterior to posterior around the ramus using a silk passing suture. Unlike the traditional PAO technique, the pubic osteotomy should have a slight reverse obliquity, allowing the fragment to rotate without impingement of the pubic segments.

The iliac osteotomy is performed with an oscillating saw. First, the ideal starting point for the posterior column cut is identified via fluoroscopy. Next, a small (1-cm) incision is made along the abductor insertion on the lateral ilium in line with the posterior column starting point, and a narrow Hohmann retractor is inserted along the lateral ilium to protect the gluteal muscles. The osteotomy is started at the lateral ilium and is directed toward the pelvic brim in a line perpendicular to the body’s longitudinal axis, aiming for the posterior column starting point. For anteverting PAOs, a standard iliac cut suffices. For true reverse PAOs, rounding of the junction of the iliac and posterior column osteotomies is beneficial for later fragment reorientation and can be facilitated with a curved osteotome.

Last, the posterior column osteotomy is created using a variety of osteotomes to connect the iliac and ischial osteotomies. First, a narrow straight osteotome is used to start the medial cut of the posterior column, using manual palpation and fluoroscopy to guide the cut. The medial cut is finished with the 30° Ganz osteotome to the level of the ischial osteotomy. Next, the iliac/posterior column corner is completely osteotomized with the Ganz osteotome. After freeing this corner, a laminar spreader is inserted to put tension across the iliac osteotomy. The lateral aspect of the posterior column cut is then made with the 30° Ganz osteotome, connecting distally to the ischial
osteotomy. At this point, the acetabular fragment should be completely freed from the remainder of the pelvis with an intact portion of the posterior column remaining.

Clinical Scenario

A 24-year-old female presented for evaluation of bilateral hip pain, left more symptomatic than the right, which had become significantly worse over a 2-year period. She had tried and failed multiple rounds of physical therapy to improve gluteal strength and pelvic positioning. She had impingement symptoms with pain on flexion (90°) and internal rotation (10°). She was evaluated with radiographs (Figure 14.1A, B) and an MRI. Her radiographs demonstrated acetabular retroversion with a large crossover sign, posterior wall sign, and ischial spine sign. All of these were most notable on her supine AP pelvis radiograph but also present on standing films. Her acetabuli had borderline lateral (23° LCEA, 8° Tönnis) and anterior coverage (20° ACEA). She had a spherical femoral head on AP imaging as well as a lateral image (not shown). MRI indicated acetabular retroversion and mild degenerative changes within the acetabular labrum, but the femoral and acetabular cartilage appeared normal. Taken together, her morphology was considered consistent with a retroverted acetabulum causing femoroacetabular impingement. She was considered a candidate for an anteverting PAO for acetabular redirection.

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