Experimental radiation synovectomy in rabbit knee with holmium-166 ferric hydroxide macroaggregate.

Holmium-166 ferric hydroxide macroaggregate (Ho-166 FHMA) particles possess two important properties for radiosynovectomy; relatively short half-life of the radioisotope and appropriate carrier size. Both these minimize radioactive leakage from the treated joint. This study was conducted to assess the effects of Ho-166 FHMA on synovium and synovial fluid in rabbit knee joints. Whole-knee autoradiography was utilized to determine distribution of radioactivity after intra-articular Ho-166 FHMA injection. Intra-articular injection of Ho-166 FHMA resulted in focal acute radiation necrosis in synovial lining but no hyperplasia of synoviocytes. Later, subsynovial fibrosis became evident. White blood cell and total protein levels in the joint fluid were elevated because of intra-articular inflammation due to the acute effects of radiation. Whole knee autoradiograms showed uneven distribution of the radionuclide along the synovium and extraarticular leakage on the third day after treatment.