Arthritis Treatment: Injection Therapy for Osteoarthritis of the Knee

The most common form of arthritis is osteoarthritis (OA). It affects almost 30 million Americans and the incidence is expected to rise with the graying of the Baby Boomers.

OA is a disease that affects the hyaline articular cartilage of joints. The exact mechanism of disease development is still being researched but there appears to be a trigger that causes a metabolic abnormality to occur. Cells, called chondrocytes, inside the cartilage begin to elaborate destructive enzymes which cause the surrounding matrix to degrade. In addition, inflammatory changes involving the synovium- the lining of the joint- contribute to further cartilage damage.

OA affects primarily weight-bearing joints such as the neck, low back, hips, and knees. I will focus on the knee.

Treatment for OA of the knee is primarily symptomatic. This involves the use of exercise, weight loss if indicated, patient education, analgesic medications, non-steroidal-anti-inflammatory drugs (NSAIDS) - either oral as well as topical, and injections.

The most common type of injection given for OA of the knee is a corticosteroid ("cortisone") injection. These are effective for reducing pain short-term and also helping to improve quadriceps muscle strength by reducing the inhibition of quadriceps reflex due to the presence of inflammation and swelling. Usually fluid is withdrawn from a swollen joint at the time of corticosteroid injection.

Corticosteroid injections are usually given to patients who are already taking oral medications such as NSAIDS. These injections may be given as often as three times a year. More often and they can actually cause more cartilage damage.

The second type of injection is hyaluronic acid. These types of injections are often referred to as viscosupplements since they are used to reduce pain but also provide a lubricating quality as well. Some preparations are derived from rooster combs and others are synthetically manufactured. There are many different formulations available. Despite claims that one product is superior to others, there is no concrete data that one preparation is superior to others.

These injections are often used as a last-ditch effort to help patients avoid having to undergo knee replacement surgery. As with corticosteroid injection, withdrawal of joint fluid always precedes injection of the viscosupplement.

Whether the injection is corticosteroid or hyaluronic acid, each needs to be administered using ultrasound needle guidance in order to ensure proper delivery of the medication to the joint space. Reports of inadequate response to these preparations probably are more related to poor injection technique rather than to the shortcoming of the medication.