Patient presents with complaints of left knee pain, swelling, and stiffness, consistent with left knee synovitis.  Symptoms include localized warmth, tenderness to palpation along the joint line, and reduced range of motion. Onset of symptoms was gradual over the past [Number] weeksmonths, possibly related to [Possible cause, e.g., overuse, recent trauma, underlying condition].  Patient denies any locking or giving way of the knee.  No history of fever or chills.  Medical history includes [List relevant medical history, e.g., osteoarthritis, rheumatoid arthritis, previous knee injuries].  Physical examination reveals palpable effusion, mild erythema, and pain with passive and active movement of the left knee.  McMurray's test is negative for meniscal tear.  No ligamentous instability noted.  Differential diagnosis includes osteoarthritis, rheumatoid arthritis, gout, pseudogout, and septic arthritis.  Initial treatment plan includes NSAIDs for pain and inflammation, rest, ice, and elevation.  Consider arthrocentesis for synovial fluid analysis to rule out infection or crystal arthropathy if symptoms persist or worsen.  Follow-up scheduled in [Timeframe] to assess response to treatment and consider further diagnostic testing such as X-ray or MRI if indicated.  ICD-10 code M65.90, Synovitis and tenosynovitis, unspecified, is considered.  Patient education provided on activity modification and importance of follow-up.