Osteoarthritis (OA) is the most common form of arthritis and affects more than 20 million Americans, costing billions of dollars in health care annually. Osteoarthritis is caused by the breakdown of joint cartilage, leading to a loss of the cartilage "cushion" between the bones of the joints. Risk factors associated with OA include age, obesity, traumatic injury and overuse due to sports or occupational stresses. There is no cure for OA and current treatments are directed at the symptomatic relief of pain, and at improving and maintaining joint function. There remains, however, a critical need both to develop OA treatments that focus on slowing down the degenerative process of the disease and for validated animal models to test these new treatments. NIH scientists at the NIDCR have generated a mouse model for osteoarthritis (FASEB J. (2002) 16, 673-680) that fills one part of this important gap.

The mouse model is a double knockout mouse that lacks biglycan and fibromodulin, two members of the small leucine-rich proteoglycan family, and that spontaneously develops OA. All the hallmarks of human osteoarthritis are present, including: progressive degeneration of the articular cartilage from early fibrillation to complete erosion, subchondral sclerosis, an absence of inflammation and development of osteophytes and cysts. Advantages over the existing models for osteoarthritis include: high phenotypic penetrance, early onset (at 1-2 months) and a rapid disease progression (between 3-6 months) which can be accelerated by moderate levels of exercise, such as treadmill running. These properties, combined with a normal life span, make the biglycan/fibromodulin-deficient mouse an ideal animal model for evaluating new drugs and treatments for osteoarthritis.