Effects of low dosage Co-60 irradiation in the course of aseptic arthritisof the knee joint of rabbits

Purpose: Numerous clinical observations demonstrate the efficacy of low rad iation doses in the treatment of painful osteoarthritis. Experimental inves tigations remain scarce. We investigated the effects of locally daily 5 tim es 1.0 Gy 60-Co irradiation on an artificially induced aseptic gonarthritis in rabbits. Material and Methods: Three separate experiments (EV) were performed (10 ra bbits per experiment, 5 treated/5 controls; duration: EV1:18 days; EV2:6 da ys; EV3:29 days). An aseptic arthritis in the right knee joint of rabbits w as induced by intraarticular injection of 0.5 ml papain solution (3%, 30,00 0 USP/mg) on day 0. The arthritic knee joint of the anesthesized animals wa s irradiated daily from day 1 to 5 with 5 times 1.0 Gy. The controls were s ham-irradiated under the same conditions. The time course of arthritis in t reated animals and sham-treated controls was evaluated by clinical, laborat ory-chemical and histological criteria. The clinical investigation was perf ormed daily, the puncture of the knee-joints was carried out several times in EV1, and at the end of experiments in EV2 and EV3. At the end of the obs ervation period, animals were killed and the knee joints excised for histol ogical analysis. Results: The intraarticular injection of papain caused a peracute inflammat ory response in all animals. After 1 week the chronical stage was reached, and the experimental arthritis resolved slowly within several weeks. Local irradiation accelerated the decrease of inflammatory joint swelling, being significant by day 4. On day 6 the volume of synovial fluid in irradiated k nee-joints was significantly smaller. The morphometric data indicated a red uction in thickness of synovial membrane, a decrease in number of synovial cell layers, and a decrease in distance between capillaries and the synovia l membrane surface following irradiation of arthritic joints. Due to consid erable individual variability, the morphometric data partially did not reac h statistically significance. Conclusion: The experiments provide evidence for an antiphlogistic effect o f irradiation with 5 times 1.0 Gy in vivo. They support the clinical observ ations of the efficacy of anti-inflammatory radiotherapy.