Defining the normal acetabular vault in adult males and females using a novel three-dimensional model

The management and quantification of bone loss is a major challenge in primary and revision total hip replacement. Defining the normal three-dimensional (3D) anatomy of the acetabular vault could aid in assessing pathologic changes and in designing prosthetic joint components. We performed a quantitative assessment of normal 3D acetabular vault structure to define the shape and location of weight-bearing acetabular bone referred to as the vault. Images from 70 normal hip computed tomography images were used to define the 3D acetabular vault anatomy and develop a 3D model. Variation in vault shape was quantified by measuring the distance between every surface point on a subject's hemipelvis and the reference vault. Variation among different hip alignments was assessed using 19 scans from subjects with varus, valgus and dysplastic hip morphologies. The acetabular vault model had 96.6% (95% CI: 91.7-101.5), 97.8% (95% CI: 94.5-101.1) and 96.4% (95% CI: 98.7-94.1) of the surface points within 3 mm of normal male, normal female and abnormal hip specimens, respectively. Comparison of acetabular vault model fit between gender and hip types revealed that it was only significantly different between normal males and normal females (P=0.0194) and between normal males and dysplastic females (P=0.0377). A conserved 3D acetabular vault shape and location exists that can accommodate various hip morphologies. Defining a normal vault may increase the precision with which hip pathology can be identified and may also serve as a preoperative assessment tool for planning total hip arthroplasty.