Pincer Deformity

A pincer deformity is acetabular overcoverage that causes premature contact between the acetabular rim and the femoral head-neck junction. The overcoverage may be focal, such as an anterosuperior prominence, or global. Arthroscopic acetabuloplasty (rim trimming) removes the pathologic rim while preserving enough acetabular coverage to maintain hip stability. This section focuses on the principles of acetabuloplasty and how to correct pincer deformities.

General steps:

1. Define the location and extent of overcoverage before surgery.

A properly positioned AP pelvis is the main study. Useful measurements include the lateral center-edge angle, Tönnis angle, and signs of acetabular retroversion such as the crossover and posterior wall signs. A CT scan may be helpful for complex, global, or revision deformities.

2. Access and exposure

Acetabuloplasty is usually performed in the central compartment under traction. After the interportal capsulotomy, the capsule and periosteal tissue are elevated from the acetabular rim. Capsular traction sutures are useful because they improve visualization without requiring unnecessary capsular excision.

The anterolateral and mid-anterior portals are commonly alternated for viewing and working. For example, the superolateral rim can be viewed from the anterolateral portal while the burr is introduced through the mid-anterior portal. Portal switching improves the angle for the more anterior rim.

3. Manage the labrum during rim trimming

The labrum should be preserved whenever possible. The amount of rim resection and the condition of the chondrolabral junction determine how it is handled.

In a small rim resection with an intact chondrolabral junction the rim can often be trimmed without detaching the labrum. The capsule and periosteum are elevated above the labrum and the burr is kept on the extra-articular side of the chondrolabral junction.

In a moderately sized rim resection, the labrum can be elevated with the capsule and subperiosteal complex. This provides access to the bone without intentionally separating the labrum from the cartilage.

In a large rim resection the labrum should be taken down and refixed as part of a labral repair. Large deformities often occur in the context of a concomitant labral tear requiring repair anyways.

4. Resect the deformity

Begin rim trimming in small, controlled passes. The anterosuperior rim is the most commonly treated region. Switch portals as needed to maintain a perpendicular, controlled burr trajectory. Keep the burr visible and keep the labrum and articular cartilage out of the cutting path. Stop frequently and reassess with fluoroscopy and arthroscopic visualization. Smooth the rim and prepare the new labral footprint if repair is required. There should be enough acetabular bone remaining to allow safe anchor placement without penetrating the articular cartilage,

Common technical problems

1. Under-resection

Residual overcoverage can leave persistent impingement.

2. Over-resection

Excessive rim trimming decreases acetabular coverage and can create iatrogenic dysplasia or instability.

3. Chondrolabral injury

An uncontrolled burr can damage the labrum or penetrate the chondrolabral junction introducing the need for labral repair when it could have been avoided.