Porth's Essentials of Pathophysiology, 4e

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Musculoskeletal Function

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changes in the synovium that occur in OA are not as pronounced, nor do they occur as early. In secondary forms of OA, repetitive impact load- ing contributes to joint failure, accounting for the high prevalence of OA specific to vocational or avocational sites, such as the shoulders and elbows of baseball pitch- ers, ankles of ballet dancers, and knees of basketball players. Immobilization also can produce degenerative changes in articular cartilage. Cartilage degeneration due to immobility may result from loss of the pumping action of lubrication that occurs with joint movement. These changes are more marked and appear earlier in areas of contact, but also occur in areas not subject to mechanical compression. Although cartilage atrophy is rapidly reversible with activity after a period of immo- bilization, impact exercise during the period of remobi- lization can prevent reversal of the atrophy. Therefore, slow and gradual remobilization may be important in preventing cartilage injury. Clinically, this has implica- tions for instructions concerning the recommended level of physical activity after removal of a cast. Clinical Features Typically, OA presents with joint pain. 60,61 Initially, pain may be described as aching and may be somewhat dif- ficult to localize. It usually worsens with use or activity and is relieved by rest. A common phenomenon, often referred to as “gelling,” involves difficulty initiating joint movement after inactivity, epitomized by the problems older people with OA have in “getting started” after sit- ting down for a while. In later stages of disease activ- ity, night pain may be experienced during rest. Cracking of joints (audible crepitus) and joint locking may occur when the joint is moved. As the disease advances, even minimal activity may cause pain. The most frequently affected joints are the hips, knees, lumbar and cervical spine, proximal and distal joints of the hands, the first carpometacarpal joint, and the first metatarsophalangeal joints of the feet. Table 44-1

identifies the joints that commonly are affected by OA and the common clinical features correlated with the dis- ease activity of each particular joint. A single joint or sev- eral may be affected. Although a single weight-bearing joint may be involved initially, other joints often become affected because of the additional stress placed on them while trying to protect the initial joint. It is not unusual for a person having a knee replacement to discover soon after the surgery is done that the second knee also needs to be replaced. Other clinical features are limitations of joint motion and joint instability. Joint enlargement usually results from new bone formation; the joint feels hard, in contrast to the soft, spongy feeling characteristic of the joint in RA. Sometimes, mild synovitis or increased synovial fluid can cause joint enlargement. Diagnosis and Treatment. The diagnosis of OA usu- ally is determined by history and physical examination, x-ray studies, and laboratory findings that exclude other diseases. 60–62 Although OA often is contrasted with RA for diagnostic purposes, the differences are not always readily apparent. Other rheumatic diseases may be superimposed on OA. Psychological factors, severity of joint disease, and educational level affect the expression of symptoms. Because there is no cure, the treatment of OA is symptomatic and includes physical rehabilitative, phar- macologic, and surgical measures. Physical measures are aimed at improving the supporting structures of the joint and strengthening opposing muscle groups involved in cushioning weight-bearing forces. This includes a balance of rest and exercise, use of splints to protect and rest the joint, use of heat and cold to relieve pain and muscle spasm, and adjusting the activities of daily living. Weight reduction is helpful when the knee is involved. The involved joint should not be further abused, and steps should be taken to protect and rest it. These include weight reduction (when weight-bearing surfaces are involved) and the use of a cane or walker if

TABLE 44-1 Clinical Features of Osteoarthritis Joint Clinical Features

Cervical spine

Localized stiffness; radicular or nonradicular pain; posterior osteophyte formation may cause vascular compression Low back pain and stiffness; muscle spasm; decreased back motion; nerve root compression causing radicular pain; spinal stenosis Most common in older men; characterized by insidious onset of pain, localized to groin region or inner aspect of the thigh; may be referred to buttocks, sciatic region, or knee; reduced hip motion; leg may be held in external rotation with hip flexed and adducted; limp or shuffling gait; difficulty getting in and out of chairs Localized discomfort with pain on motion; limitation of motion; crepitus; quadriceps atrophy due to lack of use; joint instability; genu varus or valgus; joint effusion

Lumbar spine

Hip

Knee

First carpometacarpal joint

Tenderness at base of thumb; squared appearance to joint

Proximal interphalangeal joint— Bouchard nodes Distal interphalangeal joint (DIP)—Heberden nodes First metatarsophalangeal joint

Same as for distal interphalangeal joint disease

Occurs more frequently in women; usually involves multiple DIPs, lateral flexor deviation of joint, spur formation at joint margins, pain and discomfort after joint use Insidious onset; irregular joint contour; pain and swelling aggravated by tight shoes