An Anatomical Study of the Anterosuperior Capsular Attachment Site on the Acetabulum

Despite the fact that many surgeons perform partial capsular detachment from the anterosuperior aspect of the acetabulum to correct acetabular deformities during hip arthroscopy, few studies have focused on whether these detachments influence hip joint stability. The aim of this study was to investigate the capsular attachment on the anterosuperior aspect of the acetabulum. We hypothesized that the attachment on the inferior aspect of the anterior inferior iliac spine (AIIS) is wide and fibrocartilaginous and might have a substantial role in hip joint stability. METHODS: Fifteen hips from 9 cadavers of Japanese donors were analyzed. Eleven hips were analyzed macroscopically, and the other 4 were analyzed histologically. In all specimens, the 3-dimensional morphology of the acetabulum and AIIS was examined using micro-computed tomography (micro-CT). RESULTS: Macroscopic analysis showed that the widths of the capsular attachments varied according to the location, and the attachment width on the inferior edge of the AIIS was significantly larger than that on the anterosuperior aspect of the acetabulum. Moreover, the capsular attachment on the inferior edge of the AIIS corresponded with the impression, which was identified by micro-CT. Histological analysis revealed that the hip joint capsule on the inferior edge of the AIIS attached to the acetabulum adjacent to the proximal margin of the labrum. In addition, the hip joint capsule attached to the inferior edge of the AIIS via the fibrocartilage. CONCLUSIONS: The capsular attachment on the inferior edge of the AIIS was characterized by an osseous impression, large attachment width, and distributed fibrocartilage. CLINICAL RELEVANCE: It appeared that the capsular attachment on the inferior edge of the AIIS was highly adaptive to mechanical stress, on the basis of its osseous impression, attachment width, and histological features. Anatomical knowledge of the capsular attachment on the inferior edge of the AIIS provides a better understanding of the pathological condition of hip joint instability.