Osteoarthritis (OA) of the knee is common and affects over 35% of persons 60 years of age and older. As the U.S. population ages, its prevalence is expected to rise. It results from the joint’s failure to repair damages that occur as a result of stress on the joint. While cartilage (the padding in the center of every joint) loss is fundamental, OA is a disease of the whole joint. The rate of disease progression over time differs from person to person. Symptoms include pain, stiffness, reduced joint motion, and muscle weakness. Long-term consequences include reduced physical activity, deconditioning, impaired sleep, fatigue, depression, and disability. Symptom severity and joint damage as seen on X rays is often discordant. As the disease advances, the differences seen between symptoms and joint damage can be explained by pain sensitization and tolerance, adaption to chronic pain, or reduction in activity to avoid pain.
Risk factors for OA of the knees include older age, female sex (it is more common in women), overweight or obesity, occupational factors (e.g., knee bending, heavy lifting, or squatting), and varus or valgus knee alignment. This last factor refers to angulation of the lower leg in relation to the knee. In valgus alignment, the lower leg is angled outward, or away from the midline, whereas in varus it is angled inward, or toward the midline. Recreational physical activity is not a risk factor. Pain from OA of the knee is difficult to study over time because it fluctuates and varies from individual to individual. In studies that looked at pain over time, greater pain was associated with younger age, female sex, non-white race, lower educational level, obesity, other medical factors, psychological factors like low self-esteem, and pain sensitivity.
Findings of knee OA on physical exam include crepitus (crunching of the knee during flexion), bony enlargement, reduced knee flexion, and tenderness. Redness, warmth, and swelling, if present, are mild. If these last three factors are severe, a different form of arthritis or an infection is the likely culprit. X rays and MRI scans usually show bone spurs and narrowing of the joint space, or the space between the upper and lower bones, caused by cartilage loss. There are no blood or urine tests to detect OA as there are for other forms of arthritis (i.e., rheumatoid arthritis). Likewise, joint aspiration (withdrawal of joint fluid) is not indicated routinely, and fluid may be unobtainable from many osteoarthritic knees.
Treatment of knee OA has shifted away from pharmaceuticals towards non-pharmaceutical therapy. Exercise is an essential component of the management of knee OA. Exercise goals are maintaining or improving aerobic fitness, range of motion, and strength which helps to reduce the chance of falls. An exercise regimen is often done in conjunction with and under the supervision of a physical therapist. Physical therapy, including aquatics, is usually the first course of treatment. When pain relief is necessary, the first choice is topical NSAIDs (i.e., voltaren gel). Oral NSAIDs and COX-2 inhibitors may be helpful in pain relief but do have side effects, including intestinal bleeding, and should be used with caution. They are contraindicated in anyone with heart disease as studies have implicated them in causing heart attacks. Other medications for pain relief include acetaminophen (Tylenol), duloxetine (Cymbalta), and tramadol. Opiates are never advisable for obvious reasons. Lastly, arthroscopic partial meniscectomy has been shown to give temporary relief as pain usually returns within a few years. In severe cases, knee replacement has been shown to provide marked improvement of pain and high rates of patient satisfaction.
By Peter Galvin, MDBLOG COMMENTS POWERED BY DISQUS