Neural Shape Modeling Reveals Early and Progressive Femoral Bone Shape and Cartilage Thickness Changes After Anterior...

Objective : To assess early and longitudinal post-traumatic osteoarthritis (POTA) changes in the femoral bone and cartilage following anterior cruciate ligament reconstruction (ACLR). Methods : ACLR and contralateral knees of 17 subjects (11M, 38±11years), and 17 matched healthy controls underwent 3T-MRI at 3-weeks, 3, 9, 18, and 30 months post-ACLR. Two neural shape models (NSMs): B-NSM (bone-only) and BC-NSM (bone+cartilage), trained on the Osteoarthritis Initiative (OAI), encoded femoral bone and cartilage shapes. The study endpoints were shape scores (B-Score, BC-Score), regional bone surface area, and cartilage thickness. Cross-sectional and longitudinal changes were assessed with linear mixed-effects models; η _p ² evaluated sensitivity to change. Cosine similarity compared trajectories of progressive bone and cartilage shape changes in PTOA (this data) and idiopathic-OA (OAI data). Results : At 3-weeks, ACLR knee B-Scores were significantly lower (p=0.010) than contralateral knees from surgical notchplasty. Over 30-months, ACLR knee B- and BC-Scores significantly increased (p<0.001, p<0.001) compared to baseline, with no significant change in scores of other knees. Bone surface area (η _p ² =0.01) increased from periarticular osteophyte lipping rather than subchondral plate enlargement, with concomitant region specific femoral cartilage thinning and thickening (η _p ² =0.02). B-Score (η _p ² =0.45) was more sensitive to longitudinal change than BC-Score (η _p ² =0.30). ACLR knee bone shape changes aligned with idiopathic-OA progression (cosine similarity=0.25); cartilage thickness changes did not (cosine similarity=0.09). Conclusion : Early and progressive bone remodeling and spatiotemporal cartilage thickness changes were observed post-ACLR. Both B- and B+C-Scores outperformed bone surface area and cartilage thickness measures in quantifying longitudinal changes in ACLR knees. ACLR bone shape features exhibited a linear progressive pattern similar to idiopathic-OA, while the cartilage thickness changes were nonlinear. NSM-derived, reader-independent, shape metrics of the bone and cartilage may serve as early biomarkers to study PTOA in ACLRs, or as quantitative endpoints for prevention and early-intervention trials.