Para-acetabular Radiopaque Densities in Patients With Femoroacetabular Impingement: A Retrospective Assessment of Prevalence and Characteristics.

Background: Femoroacetabular impingement (FAI) syndrome is a common source of hip pain associated with chondrolabral injury. There is a subset of patients with FAI syndrome who present with radiopaque densities (RODs) adjacent to the acetabular rim.

Purpose: To evaluate the prevalence, characteristics, and patient-specific factors associated with RODs adjacent to the acetabulum in patients treated with hip arthroscopy for symptomatic FAI.

Study Design: Case series; Level of evidence, 4.

Methods: Between November 2014 and March 2018, a total of 296 patients who underwent hip arthroscopy for FAI with a labral tear were reviewed retrospectively. Patient-specific variables were collected, including age, sex, lateral center-edge angle (LCEA), and alpha angle. Imaging (computed tomography) and surgical reports were reviewed for the location and characteristics of RODs, as well as subsequent labral treatment technique. Patients were excluded if they were treated for extra-articular hip pathology, had a revision procedure, or had a diagnosis other than FAI with a labral tear. No patient was excluded for any history of systemic inflammatory disease. Binary logistic regression was used to compare age, LCEA, and alpha angle for patients with or without radiopaque fragments. An alpha level of 0.05 was used to indicate statistical significance.

Results: A total of 204 patients met inclusion criteria; 33 patients (16.2%; 16 males, 17 females) had para-acetabular RODs. There were no statistically significant differences in age ( = .82), sex ( = .92), LCEA ( = .24), or alpha angle ( = .10) among patients with or without an ROD. Of the 33 patients, 29 (87.9%) had fragments in the anterosuperior quadrant. Overall, 31 patients (93.9%) were treated with labral repair in addition to correction of the underlying bony impingement, while 2 patients (6.1%) underwent focal labral debridement owing to poor labral tissue quality around the RODs. Twenty-five patients (76%) had identifiable RODs, which were excised at the time of surgery. The mean (± SD) ROD size measured on axial and coronal computed tomography imaging was 6.3 ± 5.5 mm and 4 ± 4.5 mm, respectively.

Conclusion: Age, sex, LCEA, and alpha angle were not predictive of the presence of para-acetabular RODs. Approximately one-sixth of all patients with FAI had RODs identified on computed tomography, which were typically located at the anterosuperior acetabulum. The majority of hips with para-acetabular RODs were amenable to labral repair. The relative prevalence and lack of predictive patient-specific indicators for these fragments suggest that a high degree of suspicion is necessary when evaluating patients with FAI.