Morphological and bone defect mapping analysis of true acetabulum in Crowe type IV hip dysplasia

The primary aim of this study was to quantitatively analysis the acetabular morphological feature and 2D/3D coverage of the Crowe IV DDH hip, dividing into subgroups by the false acetabulum. The secondary aim was to propose a 3D bone mapping to determine acetabular bone defect analysis from the perspective of the implanted simulation.

A total of 53 Crowe IV hips (27 hips without the false acetabulum in IVa group and 26 hips in IVb group) and 40 normal hips met the inclusion criteria and were retrospectively evaluated. Firstly, the anatomical size and volume of the acetabulum were measured quantitatively. Secondly, through the simulated implantation, morphological assessments of the true acetabulum included Cup-CE, Cup-Sharp, acetabular anteversion angle, and thickness of the medial wall. Last, Acetabular sector angles (ASAs) and the component coverage ratio were measured to provide coverage indices. Further, 3D bone mapping visualization was applied to determine the uncovered component portion distribution.

The anatomic shape and volume of the acetabular triangle were significantly smaller in Crowe IV hips. At the level of the acetabular component center, IVb acetabula were found to be more anteverted and abductive, with smaller Cup-CE and larger Cup-Sharp angles. The coverage sector angles in Crowe IVa hips were larger in the anterosuperior and superior direction, while smaller in the posterosuperior and posterior direction, with no subgroup difference in total component coverage. Both 3D bone mapping and correlation analysis reveal that posterosuperior and posterior bone stock is highly associated with the component coverage.

With the presence of the false acetabulum, there existed acetabular anteversion and segmental coverage distinctions between subgroups. During the acetabular reconstruction, management of posterosuperior and posterior bone stock was important for ideal component coverage.