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

Abstract

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 ( P = .82), sex ( P = .92), LCEA ( P = .24), or alpha angle ( P = .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.

Acetabular Rim Ossification Variants Are Found in Almost 20% of Patients Presenting With Hip Pain

“…They did not find any correlation to presence of “radiopaque densities” with age, sex, lateral central edge angle, or alpha angle, which differed from the current studies results. 19 Register et al. 21 found acetabular rim fractures in 11% of their patients with FAI, Clohisy et al.…”

“…Dumont et al. 19 had a prevalence of 16.2% of “radiopaque densities” in patients undergoing surgical treatment for FAI. The “radiopaque densities” were most often visualized between the 12- and 3-o’clock positions on the acetabulum, and only 66.7% of them were visible on plain radiograph as compared to computed tomography.…”

“…The reported radiographic prevalence of acetabular rim ossicles ranges from 4% to 41% in patients with symptomatic FAI and 7% to 13% in asymptomatic volunteers. 6 , 16 , 17 , 18 , 19 , 20 , 21 , 22 Radiographically, these distinct types of acetabular rim ossicles are oftentimes collectively referred to as “os acetabuli,” a term originally used to describe the secondary ossification center of the acetabulum. 4 , 8 , 16 , 18 , 20 , 22 , 23 , 24 Because this collective term has been used to describe many types of ossifications, the true prevalence of each distinct form has been difficult to determine.…”

Clinical outcomes after arthroscopic treatment of calcification with surrounding inflammation in the hip labrum

“…Byrd et al [8] reported that 56 FAI patients had calcifications of the labrum in a total of 3745 patients undergoing hip arthroscopy from 2004 to 2013. Dumont et al [9] found that para‐acetabular radiopaque densities occurred in 16% of FAI patients. The calcifications in these series were located in the anterolateral labrum, which was consistent with the area prone to labral tears.…”