Morphological features of the acetabulum with coxa profunda: A retrospective observational study

Abstract Background: Although radiographic coxa profunda is considered an indicator of acetabular over-coverage of the femoral head, recent studies do not support this. The morphological characteristics of coxa profunda are not fully elucidated. Therefore, this study aimed to verify the relationship between the pelvic characteristics and coxa profunda. Methods: This retrospective study included the data of women who had undergone unilateral total hip arthroplasty and whose pelvic anteroposterior radiographs revealed normal hip joint morphology on the contralateral side with a distance of ≥2 mm between the ilioischial line and acetabular floor. Five parameters were measured with axial computed tomography at the central hip joint and compared between the coxa profunda (n = 39) and control (n = 34) groups. Parameters included those related to acetabular anteversion and thickness and bony region position representing the ilioischial line. Results: The mean acetabular anteversion angle was 12.5 ± 4° and 22.3 ± 5.6° in the control and coxa profunda groups, respectively. The mean thickness of the acetabular fossa to the medial wall was 7.5 ± 1.7 and 3.9 ± 1.2 mm in the control and coxa profunda groups, respectively. The mean thickness of the acetabular fossa to the medial wall was 7.5 ± 1.7 and 3.9 ± 1.2 mm in the control and coxa profunda groups, respectively. The acetabulum was more anteverted (p < 0.001) and the acetabular bone was thinner (p < 0.001) in the coxa profunda group than in the control group. Additionally, the bony region representing the ilioischial line was located more posterior to the pelvis in the coxa profunda group than in the control group. Conclusion: Our results suggest that in hip radiographs showing no other significant abnormal findings, coxa profunda is related to dysplasia, with anteversion of the acetabulum and lesser anterior coverage than normal. The acetabulum is also thinner than normal in coxa profunda. These findings can be useful for formulating treatment strategies for hip disorders involving coxa profunda since coxa profunda does not indicate over-coverage as conventionally interpreted; rather, coxa profunda indicates dysplasia in the anterior part of the acetabulum.