The relationships between patellofemoral bone remodeling, cartilage composition, and vertical loading rate: PET/MRI in isolated patellofemoral osteoarthritis

Objective: Loading is invariably an important factor of consideration for understanding the causality flow and parallel existence of articular cartilage and subchondral bone changes. The goal of this study was to investigate the patterns of subregional ¹⁸NaF-SUV vs. T_1p-T₂ associations and vertical ground reaction force loading rates; in isolated patellofemoral-joint-osteoarthritis (PFJ-OA) patients.

Method: Thirty-five isolated PFJ-OA patients, with no tibiofemoral involvement, underwent simultaneous scans in a 3.0T whole-body hybrid positron emission tomography-magnetic resonance imaging scanner. MRI Whole-Organ Magnetic Resonance Imaging Scoring assessments were performed to identify/confirm isolated PFJ-OA knees from bilateral scans. T_1p-T₂ relaxation and SUV values were automatically computed for both trochlear and patellar cartilage and subchondral bone subregions (deep, superficial, lateral, and medial). Maximum vertical impact loading rates (Loading-Rate_Norm) were calculated from walking trials. Relationships were explored between SUV uptake, T_1p-T₂ values, and Loading-Rate_Norm via linear mixed-effects modeling.

Results: Significant and complex association patterns were noted between medial and lateral bone ¹⁸NaF-SUV uptakes vs. medial and lateral cartilage sub-regional T_1p and T₂. SUV_Mean and SUV_Max were positively associated with deep cartilage subregional T_1pand T₂ values; and negatively associated with superficial cartilage subregional T_1p-T₂ values in both medial and lateral regions. Both medial and lateral bone ¹⁸NaF-SUV_Mean and SUV_Max uptakes remained positively associated with the individual gait characteristics, i.e., peak vertical impact loading rates (Loading-Rate_Norm).

Conclusion: Evidence of simultaneous, complementary, cross-sectional associations between T_1p-T₂ values and peak vertical loading rates with ¹⁸NaF-SUV, have been rare in the isolated PFJ-OA cohort. The clinical implications of such novel associations remain of utmost importance from a gait retraining perspective.