Guidelines for testing slow acting drugs in osteoarthritis.

New compounds appear to improve symptoms of osteoarthritis (OA), and others are putative chondroprotective agents. We suggest experimental designs for studying the effects of these agents in subjects with hip and knee OA. The course of the articular cartilage lesion is the primary outcome measure to be assessed in putative chondroprotective agent trials. Serial radiographic studies suggest that the annual rate of joint space narrowing in patients with hip or knee OA is about 0.25 mm. Other approaches to quantitation of cartilage loss, e.g., radiographic measurement of the area of joint space, ultrasonography, magnetic resonance imaging and fiberoptic arthroscopy (for knee OA) are under investigation.