Quantifying Changes in 3D Acetabular Morphology in Normal Hips Based on the Development of Secondary Ossification Centers.

Acetabular development in pediatric hips is driven by growth from the triradiate cartilage (TRC) and secondary ossification centers (SOCs) of the os pubis, os ischium, and os ilium. These SOCs appear and fuse at different ages, with sex-specific differences affecting their morphology. This study quantifies the impact of SOCs on acetabular coverage, version, tilt, and surface area during adolescence. Three-dimensional (3D) surface reconstructions of 540 normal hips (in 128 male and 142 female patients) aged 8 to 19 years with no hip pathology were generated from computed tomography (CT) scans. Acetabular parameters, including coverage angles in predefined octants, version, tilt, and surface area, were extracted with use of a previously published algorithm. The Proximal Femur Maturity Index (PFMI) was used to assess skeletal maturity. Contributions to acetabular morphology from the 3 SOCs were analyzed using generalized linear mixed models. Significance was defined as p < 0.05. PFMI grades strongly correlated with chronological age (rs = 0.91; p < 0.001). Os ilium ossification was significantly associated with increased superior coverage (p < 0.001), and os ischium ossification was associated with increased posterior coverage (p < 0.001). Superior coverage demonstrated a strong correlation with lateral tilt (rs = 0.837; p < 0.001), and posterior coverage was strongly correlated with anteversion (rs = 0.788; p < 0.001). Female patients exhibited greater acetabular anteversion (17.7° ± 6.4° versus 12.2° ± 6.4°; p < 0.001) and lateral tilt (38.5° ± 4.7° versus 36.6° ± 5.7°; p < 0.001), whereas male patients demonstrated larger acetabular surface area (31.9 ± 6.4 versus 28.8 ± 4.2 cm2; p < 0.001). We did not find a significant association between os pubis ossification and increased anterior coverage in male (p = 0.38) or female (p = 0.065) patients, nor did we find a correlation between anterior coverage and age (p = 0.115). Os ilium and os ischium ossification were associated with increased superior and posterior acetabular coverage, respectively, during adolescence. In contrast, os pubis ossification was not associated with changes in anterior coverage. The timing of SOC appearance and closure aligns with key developmental changes in acetabular morphology, reinforcing the role of SOCs in determining hip stability. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.