Depth-specific characterization of bone microarchitecture in the femoral head: implications for osteoarthritis and osteoporosis research

Abstract Background Osteoarthritis (OA) and osteoporosis (OP) are highly prevalent musculoskeletal diseases characterized by cartilage loss and increased subchondral bone formation and by systemic bone mass reduction, respectively. The femoral head is commonly examined in both OA and OP research, yet both conditions may coexist in the same patient, making it unclear how local cartilage degeneration and systemic bone mineral density (BMD), as a marker of OP-related skeletal status, contribute to bone microarchitectural changes at different depths. Methods Femoral heads were obtained from 30 patients undergoing primary total hip arthroplasty for hip OA. Ex vivo high-resolution peripheral quantitative computed tomography (HR-pQCT) was performed on the entire femoral head, followed by computational segmentation of the subchondral mineralized plate (SMP) and five concentric trabecular regions. Depth-specific bone microarchitectural parameters were analyzed in relation to histologically assessed cartilage degeneration and systemic BMD measured by dual-energy X-ray absorptiometry (DXA). Results The cohort had a mean age of 75.4 ± 9.5 years, 53.3% were female, and patients spanned the spectrum of normal BMD (36.7%), osteopenia (46.7%), and osteoporosis (16.7%). Trabecular volumetric tissue mineral density (Tb.vTMD), bone volume to tissue volume (BV/TV), and trabecular thickness (Tb.Th) showed an initial decrease in the superficial trabecular regions, followed by a progressive increase toward deeper regions, whereas cyst-like void volume continuously decreased with depth and almost completely disappeared beyond 9.84 mm in depth. Cartilage degeneration independently predicted subchondral bone microstructure within the SMP and in superficial to intermediate trabecular regions (up to 13.12 mm in depth). Specifically, higher OARSI grades were associated with higher SMP.Th, Tb.vTMD, BV/TV, and Tb.Th. Systemic BMD T-score emerged as an independent predictor of trabecular bone parameters across all depths and represented the sole determinant of BV/TV and Tb.Th in the deepest trabecular region (beyond 13.12 mm depth), while cartilage degeneration was not associated with trabecular bone parameters in the deepest trabecular region. Conclusions Our findings showcase spatially distinct contributions of cartilage degeneration and systemic skeletal status to subchondral bone remodeling, identifying depth as a critical determinant in the analysis of osteochondral alterations in hip OA. Specifically, our findings emphasize that systemic BMD should be considered a covariate in OA research and that deep regions of the femoral head should be used for OP research to minimize potential confounding by local OA-related effects.