Upward migration of the subchondral bone plate is associated with osteochondral repair. The aim of this study was to quantitatively monitor the sequence of subchondral bone plate advancement in a lapine model of spontaneous osteochondral repair over a 1-year period and to correlate these findings with articular cartilage repair.
Standardized cylindrical osteochondral defects were created in the rabbit trochlear groove. Subchondral bone reconstitution patterns were identified at five time points. Migration of the subchondral bone plate and areas occupied by osseous repair tissue were determined by histomorphometrical analysis. Tidemark formation and overall cartilage repair were correlated with the histomorphometrical parameters of the subchondral bone.
The subchondral bone reconstitution pattern was cylindrical at 3 weeks, infundibuliform at 6 weeks, plane at 4 and 6 months, and hypertrophic after 1 year. At this late time point, the osteochondral junction advanced 0.19 [95% confidence intervals (CI) 0.10-0.30] mm above its original level. Overall articular cartilage repair was significantly improved by 4 and 6 months but degraded after 1 year. Subchondral bone plate migration correlated with tidemark formation (r = 0.47; P < 0.0001), but not with the overall score of the repair cartilage (r = 0.11; P > 0.44).
The subchondral bone plate is reconstituted in a distinct chronological order. The lack of correlation suggests that articular cartilage repair and subchondral bone reconstitution proceed at a different pace and that the advancement of the subchondral bone plate is not responsible for the diminished articular cartilage repair in this model.