The early evaluation of induced osteoarthritis in rats with 99Tcm-pertechnetate scans

Osteoarthritis was induced in 30 adult rats by serial injection of papain (3.5 mg kg-1) into the right knee on days 1, 4 and 7 of the study, with equal volumes of normal saline being injected into the left knee as a control. The severity of the induced arthritis was observed after the subcutaneous injection of 37 MBq kg-1 (1 mCi kg-1) 99Tcm-pertechnetate in the neck 24 h and 1, 2, 4, 6 and 8 weeks after the first intra-articular injection of papain. The ratio of radioactivity in the right compared with the left knee of each rat was measured as an index of the severity of osteoarthritis. After the scans, X-rays of both knees were obtained. At each state of progression, a rat was sacrificed and bilateral knee sections were performed for further pathological evaluation. The results were then compared with the changes in the radioactivity ratio and the X-rays. The radioactivity ratio of the knees reached a peak approximately 25 min after the subcutaneous injection of 99Tcm-pertechnetate and this value was chosen as the index of the severity of osteoarthritis. Marked differences in radioactivity in the left and right knees were observed as early as 24 h after the first intra-articular injection of papain. The radioactivity ratio increased with time, which correlated well with pathological changes. Joint space narrowing was not found on X-ray until 4 weeks post-injection. The results showed that the 99Tcm-pertechnetate scans correlated well with the pathological changes and that this method can detect osteoarthritis earlier than joint X-rays. It is suggested that a 99Tcm-pertechnetate scan is a useful means of evaluating early changes in induced osteoarthritis in rats.