Acetabular Ossicles: Epidemiology and Correlation With Femoroacetabular Impingement

To investigate (1) the prevalence, size, and location of acetabular ossicles in general population; (2) differentiation between the characteristic types of acetabular ossicles: unfused ossification centers (true os acetabuli), rim fractures, labral calcifications and loose bodies; and (3) correlation between acetabular ossicles, and femoroacetabular impingement (FAI) with symptoms.

Patients aged 16 to 60 years who underwent abdominal and pelvic computed tomography (CT) with non-orthopaedic indications in 2016 and patients who underwent hip arthroscopy surgery from 2010 to 2016 in our institution were included for asymptomatic and symptomatic groups, respectively. Two investigators evaluated CT images to find the prevalence, size, location of acetabular ossicles, and relationship with symptoms and FAI. We correlated them with types of ossicles.

This study included 5684 patients with 11368 hips (2790 male and 2894 female; mean age, 44.3 years) for asymptomatic group, and 264 patients with 289 hips (171 male and 93 female; mean age, 34.4 years) for symptomatic group. The prevalence of ossicles in symptomatic and asymptomatic groups was 8.65% (25/289) and 3.33% (378/11,368), respectively. The distribution of ossicles types in general population were labral calcifications (55.09%), rim fractures (35.73%), unfused ossification center (1.24%), and loose bodies (7.94%). Labral calcification had the smallest size and mostly was asymptomatic. Rim fracture was correlated with FAI in general (83.33%; P < .001) but not with any types of FAI. Size of ossicles was related with symptom (895.28 vs 103.64 mm³; P < .001).

The prevalence of acetabular ossicles in general population are 3.46%, with significantly higher prevalence of acetabular ossicles were found in symptomatic group (8.65% vs 3.33%). Size of acetabular ossicles was significantly associated with hip pain. Labral calcification was the most common type of acetabular ossicles. Significant relationship was found between rim fracture and FAI but not with any specific types of FAI.

Level III, Retrospective comparative study.