Effects of in vivo cyclic compressive loading on the distribution of local type II collagen and superficial lubricin in rat knee articular cartilage
Abstract Background This study aimed to examine the effects of a single episode of in vivo cyclic loading on rat knee articular cartilage (AC) in mid-term observation and investigate relevant factors associated with the progression of post-traumatic osteoarthritis (PTOA). Methods Twelve-week-old Wistar rats underwent one episode of 60 cycles of dynamic compression of 20 N or 50 N on their right knee joint. The spatiotemporal changes in the AC after loading were evaluated using histology and immunohistochemistry at 3 days, 1, 2, 4 and 8 weeks after loading (n=6 for each condition). The chondrocyte vitality was assessed at 1, 3, 6 and 12 hours after loading (n=2 for each condition). ResultsA localized AC lesion on lateral femoral condyle was confirmed in all subjects. The surface and intermediate cartilage in the affected area degenerated after loading, yet the calcified cartilage remained intact. The expression of type II collagen in the lesion cartilage was upregulated after loading, whereas the superficial lubricin layer was eroded in response to cyclic compression. However, the distribution of superficial lubricin gradually recovered to the normal level 4 weeks after loading-induced injury.ConclusionWe confirmed that 60 times cyclic loading exceeding 20 N could result in cartilage damage in rat knee. Endogenous repairs in well-structured joints work well with rebuilding protective layers on the lesion cartilage surface, which could be the latent factor in delaying the progression of PTOA.