An Anatomical Study of the Acetabulum with Clinical Applications to Hip Arthroscopy

BACKGROUND: The clock face has been employed to define the position of labral pathology in relation to identifiable arthroscopically relevant acetabular landmarks. The purpose of this study was to qualitatively and quantitatively describe arthroscopically relevant anatomy of the acetabulum. We aimed to present a surgical landmark that is located in close proximity to the usual location of labral pathology as an alternative to the midpoint of the transverse acetabular ligament as a reference point. METHODS: Fourteen fresh-frozen cadaveric hemipelves were dissected to evaluate osseous landmarks and relevant surrounding soft-tissue structures of the acetabulum. With use of a coordinate-measuring device, we determined the location, orientation, and relationship of key arthroscopic landmarks and the footprint areas formed by the insertions of the rectus femoris, capsule, and labrum. RESULTS: An analysis of variability of reference points around the acetabulum in relation to the anterior inferior iliac spine (AIIS) revealed that the superior margin of the anterior labral sulcus (psoas-u) was the most consistent anatomic landmark. The AIIS comprised superior and inferior facets, demarcated by the origins of the direct head of the rectus femoris and the iliocapsularis. The inferolateral corner of the footprint of the direct head of the rectus femoris was located 19.2 mm (95% confidence interval CI, 18.0 to 20.4 mm) from the acetabular rim and the inferolateral aspect of the iliocapsularis footprint, 12.5 mm (95% CI, 10.1 to 15.0 mm) from the rim. CONCLUSIONS: The superior margin of the anterior labral sulcus (psoas-u) was a reliable landmark for reference of the clock face on the acetabulum. We propose that this point, denoting 3:00, be adopted as the new standard clock-face reference for intra-articular hip structures because of its universal presence and reliable arthroscopic visualization. This marker is also beneficial because of its proximity to the typical location of labral pathology. The data presented provide a comprehensive analysis of pertinent arthroscopically relevant acetabular anatomy. CLINICAL RELEVANCE: The establishment of a new standard reference point within the acetabulum will enhance the consistency of interpretation of the location of labral pathology and improve arthroscopic orientation and navigation.