Why Exercise Therapy is Important for Knee Osteoarthritis

Exercise recommendations for people with knee osteoarthritis suggest the following:

Strength training and aerobic exercise reduce pain and improve function when knee osteoarthritis (OA) causes pain.

There are very few reasons why patients with knee OA should not exercise.

Exercise therapy for OA should be specific to each patient and prescribed by a physical therapist.

Exercise has been shown effective for knee OA even when X-rays show bone-on-bone at the joint.

Sticking with the program is the best insurance that the desired results will be achieved.

These are the findings of a group of physical therapists who took the time to review all the studies published on exercise and knee osteoarthritis (OA) up through the year 2011. Other recommendations were also posted such as the importance of exercise on reducing the worsening of knee OA and the need for lifestyle changes along with exercise for the best results.

But the area of greatest interest to physical therapists was the fact that specific muscle impairments are present in patients with knee OA. These can be changed with exercise. The term “impairments” is used instead of “weakness” because there is more going on than just a decrease in muscle strength.

Muscle impairment includes problems with muscle activation (muscle fibers contracting), muscle atrophy (wasting away), and force production. Force production refers to the ability of the nervous system to fully contract all the muscle fibers. A fully activated muscle must have the ability to fire up all the motor units at a rate that produces optimal muscle function. Failure of any of these factors to function with the correct timing and force can result in knee muscle weakness and the progression of OA.

The question has been raised whether muscle impairments cause the OA or if the OA results in muscle impairments. The answer to that question remains unknown at this time. We do know that weaker muscles (especially the quadriceps along the front of the thigh) put more pressure on the joint. This higher loading rate may be what causes the start up of the knee joint degeneration. It’s also possible that this phenomenon doesn’t initiate OA but does cause existing disease to get worse. Stronger muscles protect the cartilage and joint.

But there’s one other important factor to consider and that’s alignment of the joint. If the knee is not centered and more weight is loaded on one side over the other, the chances of developing arthritis are much greater. Combining malalignment with muscle impairments increases the risk of cartilage and joint damage. Adding obesity or being overweight to the mix further increases the risk of knee OA.

Physical therapists can take all of this information into consideration when planning an exercise program for someone with knee pain, decreased physical function, and disability associated with osteoarthritis (OA).

The question then becomes: what exercise or exercises are best to counter the muscle impairments observed in patients with knee OA? There are many other variables to consider as well. For example, which is better: exercising at home by yourself or meeting with a group? How much supervision is required and how often is it needed? Future studies are needed to fully explore these questions and provide answers that will make a difference for this patient population.