Early changes in osteochondral tissues in a rabbit model of post-traumatic osteoarthritis

Concurrent osteoarthritic (OA) manifestations in bone and cartilage are poorly known. To shed light on this issue, this study aims to investigate changes in subchondral bone and articular cartilage at two time points after anterior cruciate ligament transection (ACLT) in a rabbit model. 2 (N = 16) and 8 (N = 10) weeks after ACLT, the subchondral bone structure, cartilage thickness, Osteoarthritis Research Society International (OARSI) score, fixed charged density (FCD), and collagen orientation angle were analyzed. OA related changes were evaluated by comparing the ACLT to the contralateral (C-L) and control knees. Already 2 weeks after ACLT, higher trabecular number in the medial femoral condyle and femoral groove, greater OARSI score in the femoral condyles, and thinner trabeculae in the lateral tibial plateau and femoral groove were observed in ACLT compared to C-L knees. Only minor changes of cartilage collagen orientation in the femoral condyles and femoral groove and smaller FCD in the femoral condyles, medial tibial plateau, femoral groove and patella were observed. 8 weeks post-ACLT, the surgical knees had thinner subchondral plate and trabeculae, and smaller trabecular bone volume fraction in most of the knee locations. OARSI score was greater in the femoral condyle and lateral tibial plateau cartilage. FCD loss was progressive only in the femoral condyle, femoral groove, and patellar cartilage, and minor changes of cartilage collagen orientation angle were present in the femoral condyles, femoral groove, and lateral tibial plateau. We conclude that ACLT induces progressive subchondral bone loss, during which proteoglycan loss occurs followed by their partly recovery, as indicated by FCD results.