Effects of intraarticular injection of halopredone diacetate on the articular cartilage of rabbit knees: a comparison with methylprednisolone acetate.

Halopredone diacetate, which is a new synthetic corticosteroid drug showing local retention, and methylprednisolone acetate in common clinical use were injected into the knee joints of adult rabbits to compare the effects of the two drugs on the articular cartilage. The dosage of one injection was 1.75 mg (H-1 group) and 8.75 mg (H-5 group) for halopredone diacetate and 1.4 mg (M-1 group) and 7.0 mg (M-5 group) for methylprednisolone acetate. The drugs were injected into the right knee joint once a week, 12 times in total. One week after the last injection, the steroid crystals remaining in the knee joint were observed in all rabbits in the H-1 and H-5 groups. White deposits were seen locally on a part of the cartilage in all the rabbits in the H-1, H-5, and M-5 groups but not in the M-1 group. These white deposits were observed as cystic lesions by light microscopy and contained abundant hydroxyapatite. Other histologic findings in the articular cartilage included fissure, hypocellularity, and a decrease of proteoglycan in each group. However, no distinct difference was noted between the H-1 group and the M-1 group as regards the histological-histochemical grades of the cartilage on the medial tibial condyle or in the electron microscopic findings of the cartilage on the medial femoral condyle. The same was true for the H-5 and M-5 groups. These results show that repeated intraarticular injections of these two drugs cause severe cartilage lesions to the same degree, except for the intracartilaginous white deposits of rabbit knees.