The Effect of Acetabular Rim Recession on Anterior Acetabular Coverage

Abstract

Background: The majority of rim recession for femoroacetabular impingement (FAI) is performed anteriorly and has traditionally been assessed by the lateral center-edge (CE) angle, which correlates most closely with lateral coverage. The radiographic false-profile view permits measurement of anterior coverage via the anterior CE angle and more closely correlates with anterior coverage. Purpose: To answer the following questions: (1) How does incremental anterior rim recession change lateral and anterior CE angles? and (2) Can these changes be predicted by a formula? Study Design: Descriptive laboratory study. Methods: Twelve cadaveric hips were dissected free of soft tissue to expose the anterior acetabular rim. Incremental resections of 2.5 mm (range, 0-10 mm) were performed from the 12- to 3-o’clock position using a Dremel rotary tool. Anteroposterior hip and false-profile radiographs were obtained at each interval using a fluoroscopic C-arm. The lateral and anterior CE angles were measured by 3 orthopaedic surgeons. Results: The average preresection lateral CE angle was 35.1°, and the mean decrease in lateral CE angle from 0 to 10 mm was 9.9°; the average preresection anterior CE angle was 38.4° and the mean decrease in anterior CE angle from 0 to 10 mm was 18.2°. The anterior CE angle decreased by a factor of 1.9 when compared with the lateral CE angle (P = 2 × 10−7). The lateral CE angle decreased by approximately 1° (1.0°) per millimeter of rim recessed. The anterior CE angle decreased by approximately 2° (1.8°) per millimeter of rim recessed. Conclusion: The lateral CE angle should not be extrapolated to reflect anterior acetabular coverage. The anterior CE angle is a superior marker and predictably decreases with rim recession at double the rate of the lateral CE angle. Clinical Relevance: The false-profile view is recommended in the perioperative workup for all patients undergoing arthroscopic treatment of pincer impingement.