Three-dimensional distribution of subchondral fracture lines in osteonecrosis of the femoral head

Objective: To investigate the characteristics of three-dimensional distribution of subchondral fracture lines on the surface of the osteonecrosis femoral head, and to discuss the underlying mechanisms that contribute to its collapse. Methods: We retrospectively analyzed computed tomography (CT) images from 75 patients (comprising a total of 77 femoral heads) diagnosed with Association Research Circulation Osseous (ARCO) stage IIIA or IIIB femoral head necrosis. The three-dimensional structures of both the femoral head and the subchondral fracture line were reconstructed and subsequently fitted into normal femoral head model. A heat map of fracture line was generated to visualize its spatial distribution across the femoral heads surface.to observe its distribution. In addition to that, the femoral head was partitioned into four zones, and the frequency of each fracture line traversing different zones was calculated and analysed. Results: Highest and lowest density of subchondral fracture lines was demonstrated in anterolateral and posterolateral zone respectively. and most sparse in posterolateral. Furthermore, the three-dimensional heat map of fracture lines highlighted their most frequent occurrence in the anterolateral area, particularly near the junction of the femoral head and neck. One fracture line may pass through multiple areas, passage frequencies for fracture lines was observed in zones I, II, III and IV for 66 times (85.7 %), 52 times (67.5 %), 25 times (32.5 %) and 46 times (59.7 %), respectively, with a significant difference between zone I and other zones (P