【Objective】 To analyze histological change at patella from meniscectomized rats and subsequently to study the mechanism of pain from patella. 【Methods】 Rats were divided into 3 groups: operation (MMx)group(n=30)

sham-operation (Sham) group(n=30)

and normal (Control) group(n=30). Medial meniscus and medial collateral ligament (MCL) of right knee was resected in MMx group while reserved after being exposed in Sham group. No surgery in Control group. Then mechanical thresholds of pain were tested and histological change of cartilage and subchondral bone at patella were evaluated on 1

2

and 4 weeks post-operation. Angiogenesis at the subchondral bone was measured and molecules such as tumor necrosis factor-α(TNF-α)

vascular endothelial growth factor (VEDF)

nerve growth factor (NGF)

substance P were detected by immunohistochemistry. 【Results】 (1)The pain thresholds in MMx group declined dramatically after surgery and remained at lower level than that in Sham and Control group. (2) The patella cartilage degenerated more in MMx group in accordance with Mankin’s score of cartilage after surgery. Subchondral bone remolding occurred 2 weeks post surgery and significant change appeared 4 weeks later: blood vessels crossing the osteochondral junction

breaching tidemarks and eroded deep cartilage. The tidemarks doubled and disappeared. The thickness of subchondral bone decreased. The cartilage and subchondral bone appeared normally in Sham and Control group. (3)VEDF and NGF were identified at cartilage and TNF-α and substance P were expressed excessively around neo-vascularization at osteochondral junction in MMx group. All cytokines were detected weakly in Sham and Control group.【Conclusions】

(1)The patella from rats with MCL and medial meniscus resection presents change of osteoarthritis(OA)and the model imitate OA pain of knee joint;(2)Up-regulation of VEDF and NGF correlate with the degeneration of cartilage

remolding of subchondral bone and angiogenesis;(3)Neo-vascularization along with pain-related molecules induce mechanical hyperalgesia in the knee. Subchondral bone of patella should also be the therapeutic target of OA pain.