Patellar luxation causes abnormal mechanical loading and joint destruction in the femoral-tibial joint

Aims: Patellar luxation can cause abnormal mechanical loading and is a leading cause of patellofemoral joint damage, however its contribution to femoral-tibial joint damage is poorly elucidated. In this study, we sought to investigate the role of patellar luxation in the femoral-tibial joint in both mice and humans. Methods: In this study, we generated a patellar luxation mouse model based on the standard operating procedure of destabilization of the medial meniscus (DMM) surgery which mimics osteoarthritis (OA). Then phenotypes including gait analysis, osteophyte formation, aberrant subchondral bone remodelling, cartilage degeneration, and synovitis of femoral-tibial joint were evaluated in vivo at eight weeks after surgery. Additionally, we also performed a retrospective study to investigate femoral-tibial joint characteristics in 18 patients with post-traumatic OA or recurrent patellar luxation. Results: We found that patellar luxation caused abnormal gait and augmented osteophyte outgrowth around the tibial plateau and patella. Furthermore, micro-CT analysis showed that mice treated with patellar luxation operation exhibited aberrant subchondral bone remodelling. Intriguingly, according to Safranin-O/Fast Green staining, mice with patellar luxation showed better articular cartilage integrity and less cartilage proteoglycan damage in the medial compartment of the femoral-tibial joint. Moreover, either patellar luxation operation or DMM surgery promoted the expression of TNF-α and F4/80 in synovium tissue. However, mice subjected to patellar luxation exhibited aggressive cartilage erosion in the lateral compartment of the knee joint. In addition, the clinical study showed that patellar luxation was associated with lateral cartilage degeneration of the femoral-tibial joint. Conclusion: This study confirmed that lateral patellar luxation induced subchondral bone osteopenia, promoted osteophyte formation as well as synovial inflammation, and caused lateral cartilage rather than medial cartilage degeneration in the femoral-tibial joint.