After mechanical immobilization of the lower limb joints in experimental animals for a certain duration, articular cartilage develops clinically comparable degenerative lesions regardless of external compression, whether the joint is fixed in an extended, flexed or neutral position. Studies have demonstrated that most immobilization-induced articular cartilage damage is irreversible in rabbit knee joints after 60 days of fixation. When the immobilization period is less than 30 days, electron microscopy reveals intact superficial round protuberances and unexposed tangential fibrous bundles in articular cartilage, enabling potential lesion recovery. In contrast, immobilization exceeding 30 days leads to progressive and irreversible joint destruction. Fixed flexion positioning reduces contraction of transarticular knee muscles, resulting in atrophic alterations of periarticular bone tissue. Extended immobilization restricts joint movement and contraction of muscles and joint capsules, generating excessive compressive stress on articular surfaces and ultimately driving osteoarthritis progression. Experimental evidence further indicates that joint immobilization for fewer than 4 days initiates pathological accumulation, with both intermittent repeated immobilization and continuous fixation exerting damaging effects. Research by Okazaki et al. confirmed that extended immobilization of rabbit knee joints for 7–14 days triggers early chondrocyte degeneration; moderate cartilage damage develops at 28 days, and severe degenerative lesions occur after 42 days. The expression of P53 mRNA has been verified to play a critical regulatory role throughout this pathological process. Accordingly, stable and reproducible osteoarthritis animal models can be successfully established by rigidly fixing rabbit knee joints in the extended position for 5 to 6 weeks.

New Zealand white rabbits (male and female, 2–2.5 kg)
Modeling method: The left hind knee joint was fixed in an extended position with plaster bandage for 6 weeks to establish an osteoarthritis model.
Evaluation index: HE staining

Articular cartilage tissue HE staining