2 Materiasl and methods
2.1 Experimental animals and Cartilage damage model
New Zealand white rabbits(A total of 20 healthy adult New Zealand white rabbits with body weight in 3.0-3.5kg,male and female unlimited)were obtained from the Experimental Animal Center of Anhui Medical University.All procedures were approved by the Anhui Medical University Laboratory Animal Ethics Committee(approval number:LLSC20210237).We used Borrelli’s method to modify the animal model of impingement cartilage injury in rabbit knee joint.After adaptive feeding for 1 week, rabbits were modeled. The specific method was as follows: the supine position was taken, and the pelvis and thigh were fixed. Anesthesia with 10% chloral hydrate and hair removal at both knees. A longitudinal incision of about 3 cm was made on the medial side of one knee joint. The rabbit patella was everted, the knee joint was flexion and extension 120°, and the femoral shaft was 90°. A 1kg impingent was used to fall down from a height of 50 cm along the guide rod and impinged on the medial femoral condyle, causing cartilage damage on the medial femoral condyle.All rabbits were sacrifificed in a CO2 chamber at 4 weeks post-surgery and knee joints were collected for MRI imaging and immunohistochemistry (IHC) staining.