To evaluate the histological changes of the synovial membrane treated by 166Ho-Chitosan complex in collagenase induced arthritis of the knee in the rabbit.

Arthritis was induced in sixteen rabbits by intra-articular injection of 1mg collagenase II and then treated by intra-articular injection of 0.4mCi 166Ho-Chitosan complex 2weeks later. The radioisotope scan was checked in each rabbit for the distribution and extra-articular leakage of the 166Ho-Chitosan complex. The synovial tissues from the femorotibial joints were evaluated for serial histological changes 2, 4, 8, 12 weeks after the 166Ho-Chitosan complex injetion.

Two weeks after 166Ho-Chitosan complex administration, inflammatory cells such as giant cells, lymphocytes, histiocyte, and fibroblasts appeared in the subsynovial stroma. The most synovial cells were necrotized. Four weeks after 166Ho-Chitosan complex administration, the inflammatory cells were decreased and many fibroblasts appeared on the subsynovial stroma. There was neovasculization in the synovial membrane 4 weeks after administration. The fibers of collagen were noticed in the synovial membrane and subsynovial stroma at 8 weeks. There was no synoviocyte in the synovium and the thickness of fibrosis was increased at 12weeks. There were fragmentation of the nucleoli of synoviocyte and endothelial cell on the transmission electron microscope (TEM).

This study suggests that the synovial membranes treated by 166Ho-Chitosan complex in the collagenase induced arthritis of the knee in the rabbit show early radiation damage and then subsequently develop the fibrosis, and no synovial cell regeneration was observed until 12 weeks.