Three-dimensional morphological analysis of true acetabulum in Crowe type IV hip dysplasia via standard-sized cup-simulated implantation.

Background: Acetabular reconstruction in Crowe type IV developmental dysplasia of the hip (DDH) can be a challenging procedure for surgeons. A high risk of acetabular revision has been reported to be associated with extremely small acetabular prostheses. However, to our knowledge, quantitative morphological and coverage evaluations of the true acetabulum in Crowe IV hips have been infrequently conducted. Useful bony landmarks for acetabular reconstruction can also facilitate satisfactory intraoperative implantation. The aim of the present study was to investigate the anatomical size, orientation angles, and 2/3-dimensional (2D/3D) coverage parameters of the true acetabulum in Crowe IV hips; evaluate the feasibility of standard cup (>44 mm) implantation at the true acetabulum in Crowe IV hips; and identify the optimal position and useful bony landmarks of the acetabular reaming center in Crowe IV hips. Methods: A total of 42 Crowe IV hips in 37 patients and 36 normal hips were included in this study. Based on pelvic 3D computed tomography (CT) reconstruction, anatomical size and integral volume of the true acetabulum were measured quantitatively. Through standard-size cup-simulated implantation, morphological assessments of the true acetabulum included Cup-CE, Cup-Sharp, acetabular anteversion angle, and thickness of the medial wall. Acetabular sector angles (ASAs) and the component coverage ratio were measured to provide coverage indices. Acetabular reconstruction was also performed at different vertical levels to measure medial bone stock and 3D component coverage. Bony landmarks for optimal component center location were also determined. Results: The anatomic shape and volume of the acetabular triangle were significantly smaller in Crowe IV hips. Compared with the control group, the dysplastic acetabulum was more anteverted and abductive, with a thicker medial wall. According to the true acetabulum, bone stock was relatively sufficient in the posterior direction and prominently deficient in the anterosuperior and superior direction. The average 3D component coverage reached 79.89% by standard-sized cup implantation, with the most satisfactory coverage achieved at the true acetabulum (at the level of 13.32 mm above the transverse acetabular ligament). Regarding the component opening plane, the optimal component center was located at the midpoint between the superolateral and posteroinferior points of the true acetabulum. Conclusions: The most satisfactory coverage was achieved at the level of the true acetabulum, of which the most prominent deficiency was mainly located in the anterosuperior and superior directions. The optimal component center was determined to be the midpoint between the superolateral and posteroinferior points of the true acetabulum.