Osteoarthritis (OA) is the most common form of arthritis and affects roughly 30-40 million Americans. The condition is due to a metabolic disorder of cartilage, the gristle that caps the ends of long bones. Cartilage functions to cushion the joint against impact and also to allow gliding of the joint with movement.

Cartilage consists of cells called chondrocytes that sit inside a matrix- much like grapes inside of gelatin. Normally, chondrocytes produce substances that build up and nourish the matrix. When osteoarthritis develops, the chondrocytes begin to function abnormally and no longer elaborate normal matrix.

Instead, chondrocytes begin to produce destructive enzymes that weaken the matrix. Small cracks in cartilage develop. At the same time, the lining of the joint (synovial capsule) is stimulated to produce inflammatory enzymes that further weaken cartilage. The end result is loss of cartilage. As cartilage wears away, the joint begins to become mechanically unbalanced leading to more damage.

Conventional treatment for osteoarthritis of the knee consists of patient education, maintenance of ideal weight, supplements such as good quality forms of glucosamine/chondroitin, bracing, lateral wedge insoles, non-steroidal anti-inflammatory drugs, injections of glucocorticoids (steroids), injections of viscosupplements, and sometimes surgery. (All of these have been described in previous articles by me).

One often neglected but critical component of treatment is exercise. A recent review discussed the importance of exercise and reached some interesting conclusions. (Bennell K, Hinman R. Current Opin Rheumatol. 2005; 17: 634-40)

Benefits of exercise appear to be additive when exercise is delivered with other interventions such as weight loss.

Types of exercise include strengthening, stretching, and non impact aerobic exercise, all of which are important and which work synergistically.

It appears that supervised exercise sessions are superior to home exercises for pain reduction. The challenge is to convince patient so the importance of exercise. One interesting question is whether exercise can prevent disease or slow its progression.

Also it is apparent that certain patient subgroups that may respond differently to treatment. It has been substantiated that one major risk factor for the development and progression of knee OA is weak quadriceps muscles. This is especially true for women. As a result, if strength training is administered to this high risk group, it may be able to prevent knee osteoarthritis.

According to the authors, novel exercise programs that strengthen hip muscles or alter impairments in knee neuromuscular control may also influence disease progression.

They conclude that "Future studies must identify cost-effective exercise modes, strategies to maximize exercise compliance and optimal treatment combinations. The role of muscle strength and altered neuromuscular control in the prevention and development of osteoarthritis must be evaluated with the view to devising and testing novel exercise interventions."

As a rheumatologist who sees many many patients with OA of the knee, I encourage a comprehensive exercise program along with many of the other treatments described above. No one treatment will work for a patient. However, the right combination of treatments will work for almost all patients. Exercise is an oft-neglected but important component of a comprehensive knee care program with OA.