Osteoarthritis (OA) is a debilitating condition affecting over 21 million persons in the United States. This number is expected to rise in the coming decades. Treatment approaches for OA focus on symptom modifying measures (i.e., pain relief) as disease modifying interventions do not currently exist. However, some of the interventions used to alleviate the symptoms of OA are also thought to have disease-modifying benefits. Two such non-surgical interventions for OA are intra-articular hyaluronan (HA) injections and physical exercise. In order to effectively study their effects in human OA, animal models that are amenable for studying intervention outcomes are needed.

The research focused on developing and characterizing a progressive non-surgical model of knee OA in adult mice. This model was used to firstly, examine the capacity of intra-articular HA injections to prevent knee joint degeneration, and secondly to examine the capacity of moderate exercise to prevent onset and progression of joint degeneration.

Intra-articular injections of TGF-β1 into murine knees produce synovial hyperplasia, osteophyte formation, and fibrotic changes on cartilage surfaces and joint capsules. However, additional exposure of the joints to high intensity treadmill running (biomechanical overuse) results in more widespread and focal OA-like cartilage erosions of both the tibial and femoral surfaces, similar to that described for the pathological appearance of late human knee OA. Taken together, these data support that synovitis and soft-tissue activation in early OA joints may precede and/or accelerate the process cartilage degeneration characteristic of progressive and late stage osteoarthritis.

Intra-articular injections of high molecular weight HA one day following TGF-β1 injections resulted in decreased synovial hyperplasia, minimized osteophyte formation, and significantly decreased severity of cartilage lesions. A four week, alternate day, low intensity aerobic treadmill running program prior to TGF-β injections and overuse also resulted in decreased severity of cartilage lesions.