Regional and depth-dependent associations between subchondral bone and cartilage in hip osteoarthritis: a preliminary...

To explore regional and depth-dependent associations between subchondral bone metabolic activity and adjacent cartilage composition in individuals with mild-to-moderate hip osteoarthritis using simultaneous [¹⁸F]-sodium fluoride (NaF) positron emission tomography (PET) and quantitative magnetic resonance (MR) imaging.

In this exploratory cross-sectional study, 14 participants (28 hips) underwent [¹⁸F]-NaF PET/MR imaging. Subchondral bone metabolic activity was quantified using standardized uptake values (SUV); cartilage composition was assessed using T_1ρ and T₂ relaxation times. PET/MR images were registered to a reference space allowing regional cartilage and adjacent bone analysis across subregions and depths (4-16 mm from the articular surface). Linear mixed-effects models adjusted for age were used to explore regional differences and cartilage-bone relationships with false discovery rate (FDR) correction.

Higher T_1ρ and T₂ relaxation times were observed in the overall femoral cartilage compared with the acetabular cartilage, whereas higher SUV was observed in the acetabulum than in the femur. Within the femur, elevated SUV was observed in the femoral neck. No cartilage-bone relationships remained statistically significant after FDR correction. Exploratory analyses without the FDR correction suggested positive and negative regression coefficients between cartilage relaxation times and adjacent femoral bone SUV in the posterior and anterior femoral head regions. The magnitude and direction of these coefficients were consistent across increasing bone depths.

This preliminary study presents an exploratory framework for assessing region and depth-specific interactions between subchondral bone metabolic activity and cartilage composition in the hip. The observed patterns are hypothesis-generating and warrant confirmation in larger, longitudinal studies.