1. Gout affects primarily the first MTP joint in addition to other joints of the foot and lower extremity. Tophaceous deposits over the small joints of the hand may be confused with osteophytes. The diagnosis of gout is confirmed by the identification of urate crystals in the joint fluid (see Chapter^.).
2. Calcium pyrophosphate dihydrate arthritis (pseudogout) may coexist with OA. The wrist, shoulder, knee, and ankle joints are commonly involved. Radiographs reveal chondrocalcinosis in most pseudogout patients. The diagnosis is confirmed by identifying birefringent, rhomboidal CPPD crystals in the joint fluid (see Chapter.38). Another type of crystal, basic calcium phosphate, is implicated in the pathogenesis of the destructive OA variant known as Milwaukee shoulder syndrome.
D. Other disorders that may coexist with OA but are important to identify and treat include the following:
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