Abstract: BACKGROUND: Cartilage injury is one of the important pathological manifestations of knee osteoarthritis (KOA). Tongluo Analgesic Gel is prepared on the basis of Tongluo Analgesic Formula, using carbomer, gelatin and other compounds with good biocompatibility as carriers, which can be directly applied to the affected area, and is more convenient for patients to carry and use.   
OBJECTIVE: To observe the effects of Tongluo Analgesic Gel on cartilage inflammation and degeneration in rabbits with different degrees of KOA, and to preliminarily explore the mechanism of Tongluo Analgesic Gel in treating KOA. 
METHODS: Fifty-six male rabbits were randomly divided into eight groups, namely: control group; sham operation group; mild KOA group; moderate KOA group; severe KOA group; Tongluo Analgesic Gel intervention for mild, moderate, and severe KOA groups. Except for the control group and the sham operation group, KOA models were established in the other groups using the modified Hulth method. Rabbits in the mild, moderate and severe KOA groups were sacrificed at 4, 8 and 16 weeks after modeling, respectively. In the three intervention groups, 3-week intervention with Tongluo Analgesic Gel were given, 1 mL once, 3 times a week beginning at 4, 8, and 16 weeks after modeling, respectively. The changes of knee joint diameter before and after modeling in each group were observed. Hematoxylin-eosin staining was performed to observe the morphological changes of cartilage tissues in each group. RT-qPCR and western blot methods were used to detect the changes of expression levels of interleukin-1β, tumor necrosis factor-α, matrix metalloproteinase-13 and disintegrin-like metalloproteinase with thrombospondin motifs-5 (ADAMTS-5) in cartilage tissue. 
RESULTS AND CONCLUSION: The diameter of the right knee joint of rabbit models established using the modified Hulth method was significantly increased compared with the control group and sham operation group, and it changed with time (P < 0.05, P < 0.01). After treatment with Tongluo Analgesic Gel, the diameter of the right knee joint was significantly decreased, especially in the mild and moderate KOA models (P < 0.01). The hematoxylin-eosin staining results showed that the morphological changes of cartilage tissues in the sham operation group were not significantly different from those in the blank group. The cartilage surface of the mild, moderate, and severe KOA groups was uneven, with disordered layers and delamination, whereas the cartilage surface became slightly smooth and flat after intervention with Tongluo Analgesic Gel. Compared with the control group, the expression levels of interleukin-1β, tumor necrosis factor-α, matrix metalloproteinase-13 and ADAMTS-5 in the mild, moderate and severe KOA groups were significantly increased, while Tongluo Analgesic Gel could significantly inhibit these expression levels in the KOA models (P < 0.05, P < 0.01), especially in the mild and moderate KOA groups (P < 0.01). To conclude, Tongluo Analgesic Gel can significantly inhibit cartilage inflammation and delay cartilage degeneration in rabbits with different degrees of KOA, especially in mild and moderate KOA rabbits. 

Key words: bone, osteoarthritis, knee, cartilage degeneration, gel, inflammation, factor, rabbit, experiment