Experimental osteoarthritis in the rabbit. I. Histological changes of the synovial membrane.

Based on an experimental model of osteoarthritis in 42 full-grown rabbits the histological changes were studied during the development of osteoarthritis after operative induction of instability of the knee joint. The changes were followed from 2 week to 1½ years after the induction. The first changes were observed at 1 week stage as a proliferation of the lining cells. During the time of observation additional changes were seen such as hypertrophy of villi, infiltrations with plasma cells and lymphocytes, increased vascularity and interstitial edema and fibrosis. Edema was only seen during the first months, later increasing fibrosis was predominant. The first cartilage change was reduction of the staining ability, expressing depletion of GAG, this was seen already at the one week stage whereas morphological changes were present after 4–6 weeks. It was concluded that the synovial membrane in this model shows changes that may contribute to the development of osteoarthritis.