Neural Shape Modeling Reveals Early and Progressive Femoral Bone Shape and Cartilage Thickness Changes After Anterior Cruciate Ligament Reconstruction

ObjectivesTo assess early and longitudinal post-traumatic osteoarthritis (POTA) changes in the femoral bone and cartilage following after anterior cruciate ligament reconstruction (ACLR). MethodsACLR 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; p2 evaluated sensitivity to change. Cosine similarity compared trajectories of progressive bone and cartilage shape changes in PTOA (this data) and idiopathic-OA (OAI data). ResultsAt 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 (p2=0.01) increased from periarticular osteophyte lipping rather than subchondral plate enlargement, with concomitant region-specific femoral cartilage thinning and thickening (p2=0.02). B-Score (p2=0.45) was more sensitive to longitudinal change than BC-Score (p2=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). ConclusionEarly 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.