An accurate history and a thorough examination must precede special tests that are to confirm the diagnosis of OA. Currently there is no single reliable diagnostic test; thus a step-wise approach is employed. In straightforward symptomatic cases, plain radiography is often all that is necessary to confirm the diagnosis. If the process is thought to be linked to crystal deposition disease or secondary to an inflammatory arthropathy, a full workup including urate levels, full blood count, erthyrocyte sedimentation rate, C-reactive protein, rheumatoid factor, and autoantibody screen may be indicated.
Table 1.1. Kellgren and Lawrence radiographic scale for osteoarthritis 
0 No features of osteoarthritis
1 Doubtful; minute osteophyte of doubtful significance
2 Minimal; definite osteophyte but joint space unimpaired
3 Moderate; moderate diminution of joint space
4 Severe; joint space severely impaired with sclerosis of subchondral bone
Plain radiography may be unremarkable in the early stages, but joints exhibiting classic disease demonstrate characteristic features, as noted by Kellgren and Lawrence , who encouraged the classification of OA solely on radiologic grounds (Table 1.1). Alternative grading systems have evolved since the
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