[Morphological changes in the knee joint of rat by intra-articular injection of vitamin A]

Morphological changes in the rat knee joint were induced by intra-articular injection of vitamin A. Rats were divided into low (7500 IU) and high (50000 IU) dosage groups based on the dosage of vitamin A administered. Changes in the synovium, bone and cartilage in the joints were histologically investigated. Quantitative analysis was also carried out: for changes in the synovium, the number of lymphocytes, lining cells and endothelial cells were counted; for bone changes, the number of osteoclasts, eroded surface (%ES), depth of eroded cavity (Dec), formation surface (%FS) and width of new bone (Wnb) were evaluated; and for changes in the joint cartilage, a modified histologic-histochemical grading system was used. In the low dosage group, many eosinophils infiltrated into the synovium, and bone-eroded lesions composed of inflammatory granulation and many osteoclasts were observed in the transitional region from the articular cartilage to the synovium after 1 week, the first week of the evaluation. In the high dosage group, similar bone-eroded lesions were observed after 4 weeks, the first week of the evaluation. In both groups after 4 weeks, these bone-eroded lesions were accompanied by new bone formation. As to the histomorphometry, the number of osteoclasts, %ES and Dec in the high dosage group after 4 weeks were significantly greater than those in the low dosage group. %FS were significantly higher after 4 and 8 weeks but not significantly different after 12 weeks. Wnb was significantly higher after 4 weeks but not significantly different after 8 weeks. These bone-eroded lesions were dosage dependent. There were no apparent changes observed in the joint cartilage. These results suggested that vitamin A induced eosinophil infiltration into the synovium, and that the transitional region was the main reactive site for vitamin A in the rat knee joint.