Correct orientation of the acetabular shell component within the pelvis is believed to be a significant factor in determining the risk of dislocation, aseptic loosening of the implant within the surrounding bone, component wear, and osteolysis in patients undergoing Total Hip Arthroplasty (THA). Current image-guided computer-assisted THA bases abduction and anteversion angles of the acetabular component relative to the anterior pelvic plane (APT), which is derived from the bilateral anterior superior iliac spine (ASIS) and pubic tubercles (PT). Determination of the APP relies on accurate identification of these bony landmarks through palpation. Difficulties in accurately locating bony landmarks through palpation, variability of the pelvis location inside the body as well as in patient position on the operating table, make for highly inconsistent definition of the APP. This high variability can cause misaligned THA components which can limit surgical success²⁶.

This study aimed to find a set of repeatably identifiable bony landmarks from two-dimensional digitally reconstructed radiographic (DRR) images that would define a novel pelvic reference frame to orient acetabular components during THA. Twenty orthopaedic surgeons identified twelve bony pelvic landmarks on DRR images taken of one pelvis from varying views. Analyses of standard deviation data from landmark location data recorded from these DRR images were used to determine the optimal landmarks and DRR views to create a new pelvic reference frame. The ASIS, PT, and ischial tuberocity (IT) of the affected side of the pelvis were the most repeatably identified landmarks in anterior and lateral DRR views. The reference frame created by these landmarks, the Oblique Pelvic Plane (OPP), was compared to the APP using sensitivity and repeatability analyses. The OPP showed lower variability compared to the APP in relation to the acetabular plane. The OPP has potential to become an alternate reference frame in the pelvis for orienting acetabular components during image-guided computer-assisted THA.