Complete Circumferential Osseous Extension in the Acetabular Rim Occurs Regardless of Acetabular Coverage.

BACKGROUND: Complete circumferential osseous extension in the acetabular rim has been reported to occur in the deep hip with pincer impingement. However, this phenomenon occasionally is observed in dysplastic hips without pincer impingement, and the degree to which this finding might or might not be associated with hip pain, and how often it occurs bilaterally among patients, are not well characterized. QUESTIONS/PURPOSES: (1) To determine the proportion of patients with complete circumferential osseous extension in the acetabular rim using three-dimensional (3-D) CT in patients with and without hip pain who had CT scans obtained for various reasons. (2) To elucidate how often this complete circumferential osseous extension occurred bilaterally among those patients. (3) To investigate the relationship between the proportions of patients with complete circumferential osseous extension observed on CT scans among three different acetabular coverage groups: dysplasia, normal, and overcoverage. (4) To determine how often the finding of hip pain was associated with complete circumferential osseous extension. PATIENTS AND METHODS: Between September 2011 to July 2016, we evaluated 3788 patients with pelvic complaints such as hip, groin, thigh, buttock, or sacroiliac joint pain. We obtained consent from 26% (992 of 3788) of them, and obtained 3-D CT scans as part of that evaluation. For the current retrospective study, we excluded patients younger than 20 years or 80 years or older (181 patients), patients who had previous hip surgery (185 patients), patients with severe osteoarthritis with Tönnis Grades 2 or 3 (301 patients), and patients who could not have an accurate lateral center-edge (LCE) angle measured owing to poor-quality radiographs (24 patients), leaving 301 patients (602 hips) for this analysis. In this study population, patients reported pain in 131 hips (22%), defined as all types of hip pain except for trauma, including activity pain, pain with sports, pain on motion, and impingement pain; the others did not report hip pain. The mean age of the patients was 56 ± 16 years, and the mean LCE angle was 26° ± 8° (range, -9° to 47°). We first determined the proportion of patients with complete circumferential osseous extension in the acetabular rim using 3-D CT for those with and without hip pain who had CT obtained for various reasons. We next elucidated how often this complete circumferential osseous extension occurred bilaterally among the patients, and finally we investigated the relationship between the proportion of patients with complete circumferential osseous extension observed on CT scans among the three groups: dysplasia (defined as LCE angles of 22° or smaller), normal, and overcoverage (defined as LCE angles of 34° or larger) groups. We finally determined how often the finding was associated with hip pain attributable to complete circumferential osseous extension. RESULTS: The proportion of patients with complete circumferential osseous extension was 6% (18 of 301 patients). Eighty-nine percent (16 of 18) of the patients had bilateral complete circumferential osseous extension. There were no differences in the proportions of patients with complete circumferential osseous extension among the three groups: 5.3% (odds ratio [OR], 1.02; 95% CI, 0.45-2.31; p = 0.97), 5.3%, and 7.4% (OR, 0.70; 95% CI, 0.28-1.73; p = 0.44) in the dysplasia, normal, and overcoverage groups, respectively, with the numbers available. Eighteen percent (six of 34) of the hips with complete circumferential osseous extension had pain. CONCLUSIONS: Complete circumferential osseous extension in the acetabular rim is relatively uncommon. When it occurs, it usually is bilateral, it occurs regardless of acetabular coverage, and it is associated with pain in a minority of patients. LEVEL OF EVIDENCE: Level III, prognostic study.

Focal concavity of posterior superior acetabulum and its relation with acetabular dysplasia and retroversion in adults without advanced hip osteoarthritis.

BACKGROUND: Although little is known, a limited number of three-dimensional computed tomography (CT) images of the pelvis present focal concavity of posterior superior acetabulum. The purpose of the present study was to investigate this morphologic deformity and its relation with dysplasia and retroversion in adults who were expected to have the original morphology of the acetabulum after growth. METHODS: Consecutive adult patients with hip pain who visited our hospital and had three-dimensional pelvic CT images were retrospectively analyzed after approval of the institutional review board; exclusion criterions included diseases, injuries and operations that affect the morphology of the hip including radiographic osteoarthritis Tönnis grades 2 and 3. Focal concavity of posterior superior acetabulum was evaluated by three-dimensional CT image. Acetabular dysplasia was determined by lateral center edge (LCE) angle <25°, Tönnis angle >10°, and anterior center edge (ACE) angle <25° on standing hip radiographs. Acetabular version angle was measured at the one-fourth cranial level of axial CT image. A subgroup analysis included only younger adult patients up to 50 years. RESULTS: The subjects analyzed were 46 men (92 hips) and 54 women (108 hips) with a median age of 57.5 (21-79) and 51.0 (26-77) years, respectively. Focal concavity of posterior superior acetabulum was observed in 13 hips; 7 patients had unilaterally, while 3 patients showed bilaterally. Among these hips, pain was observed in 8 hips but 4 hips (2 patients) were associated with injuries. This morphologic abnormality was not associated with acetabular dysplasia determined by LCE angle <25°, Tönnis angle >10° or ACE angle <25°. Of note, no acetabulum with the deformity plus dysplasia was retroverted. These findings were confirmed in a subgroup analysis including 22 men (44 hips) and 27 women (54 hips) with a median age of 31.0 (21-50) and 41.0 (26-50) years, respectively. CONCLUSIONS: Focal concavity of posterior superior acetabulum could be a rare morphologic abnormality of acetabular formation independent of lateral or anterior dysplasia or retroversion.