Osteoarthritis is disease of joints. The diagnosis of osteoarthritis is usually based on clinical and radiographic feactures. In the early stages, the radiograph may be normal, but joint space narrowing becomes evident as articular cartilage is lost. Other characteristic radiographic findings include subchondral bone sclerosis, subchondral cysts, and osteophytosis.
A change in the contour of the joint due to bony remodeling and subluxation may be seen.
Although tibiofemoral joint space narrowing has been considered to be a radiographic surrogate for articular cartilage thinning, in patients with early OA who do not have radiographic evidence of bony changes (e.g., subchondral sclerosis or cysts, osteophytes), joint space narrowing alone does not accurately indicate the status of the articular cartilage.
Similarly, osteophytosis alone, in the absence of other radiographic features of OA, may be due to aging rather than to OA.
As indicate above, there is often great disparity between the severity of radiographic findings, the severity of symptoms, and functional ability in OA. Thus, while more than 90 percent of persons over the age of 40 have some radiographic changes of OA in weight-bearing joint, only 30 percent of these persons are symptomatic.
No laboratory studies are diagnosis for OA, but specific laboratory testing may help in identifying one of the underlying causes of secondary OA.
Because primary OA is not systemic, the erythrocyte sedimentation rate, serum chemistry determinations, blood counts, and urinalysis are normal.
Analysis of synovial fluid reveals mild leukocytosis (<2000 white blood cells per microliter), with a predominance of moninucler cells.
Synovial fluid analysis is of particular value in excluding other conditions, such as calcium pyrophosphate dehydrate deposition disease, gout or septic arthritis.
Prior to the appearance of radiographic changes, the ability to clinically diagnose osteoarthritis without an invasive procedure e.g., arthroscopy is limited. Approaches such as magnetic resonance imaging and ultrasonography have not been sufficiently validated, and their limits of resolution and cost do not justify their routine clinical use for diagnosis of osteoarthritis or monitoring of disease progression.
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