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Differential Diagnosis
Rheumatoid arthritis is a close differential of osteoarthritis. The distinguishing features of rheumatoid arthritis include morning stiffness lasting for ≥60 minutes, the presence of positive rheumatoid factor and/or anti-cyclic citrullinated peptide (anti-CCP) antibody, and increased ESR and C-reactive protein (CRP) levels.
Septic arthritis should also be ruled out, where it presents with a positive synovial fluid culture. Seronegative arthritis such as inflammatory arthropathies which affect >1 joint including ankylosing spondylitis and reactive arthritis (recent history of an infection, usually of the urinary tract, precedes joint pain) may also be considered. Another form of seronegative arthritis, psoriatic arthritis, in which patients may also present with psoriasis, should likewise be considered.
Other differential diagnoses include crystal arthropathies such as gout, which is suspected in patients with increased serum uric acid levels and the presence of tophi; and pseudogout where there is the presence of calcium pyrophosphate crystals on synovial fluid analysis.
If there is a sudden onset of pain after strenuous activity, ligament injury may be considered.