Osteoarthritis (OA) is the most common type of arthritis. Its high prevalence, especially in the elderly, and the high rate of disability related to disease make it a leading cause of disability in the elderly. Because of the aging of Western populations and because obesity, a major risk factor, is increasing in prevalence, the occurrence of osteoarthritis is on the rise. In the United States, osteoarthritis prevalence will increase by 66–100% by 2020.
OA affects certain joints, yet spares others (Fig. 332-1). Commonly affected joints include the cervical and lumbosacral spine, hip, knee, and first metatarsal phalangeal joint (MTP). In the hands, the distal and proximal interphalangeal joints and the base of the thumb are often affected. Usually spared are the wrist, elbow, and ankle. Our joints were designed, in an evolutionary sense, for brachiating apes, animals that still walked on four limbs. We thus develop OA in joints that were ill designed for human tasks such as pincer grip (OA in the thumb base) and walking upright (OA in knees and hips) Some joints, like the ankles, may be spared because their articular cartilage may be uniquely resistant to loading stresses.
Joints affected by osteoarthritis.
OA can be diagnosed based on structural abnormalities or on the symptoms these abnormalities evoke. According to cadaveric studies, by elderly years, structural changes of OA are nearly universal. These include cartilage loss (seen as joint space loss on x-rays) and osteophytes. Many persons with x-ray evidence of OA have no joint symptoms and, while the prevalence of structural abnormalities is of interest in understanding disease pathogenesis, what matters more from a clinical perspective is the prevalence of symptomatic OA. Symptoms, usually joint pain, determine disability, visits to clinicians, and disease costs.
Symptomatic OA of the knee (pain on most days of a recent month in a knee plus x-ray evidence of OA in that knee) occurs in ∼12% of persons age ⩾60 in the United States and 6% of all adults age ⩾30. Symptomatic hip OA is roughly one-third as common as disease in the knee. While radiographically evident hand OA and the appearance of bony enlargement in affected hand joints (Fig. 332-2) are extremely common in older persons, most cases are often not symptomatic. Even so, symptomatic hand OA occurs in ∼10% of elderly individuals and often produces measurable limitation in function.
Severe osteoarthritis of the hands affecting the distal interphalangeal joints (Heberden's nodes) and the proximal interphalangeal joints (Bouchard's nodes). There is no clear bony enlargement of the other common site in the hands, the thumb base.
The prevalence of OA rises strikingly with age. Regardless of how it is defined, OA is uncommon in adults under ...