Red flags The following findings are of particular concern: Erythema, warmth, effusion, joint capsule tenderness, and decreased range of motion Fever with acute joint pain Acute joint pain in a sexually active young adult Skin breaks with signs of cellulitis adjacent to the affected joint Underlying bleeding disorder or use of anticoagulants Systemic or extra-articular symptoms Interpretation of findings Recent significant trauma suggests that injury is the cause (eg, fracture, meniscal tear, or hemarthrosis).