Copyright 2009
Definition
Gout of the knee is a common disorder of uric acid metabolism that can lead to deposition of monosodium urate (MSU) crystals in soft tissue, recurrent episodes of debilitating joint inflammation, and, if untreated, joint destruction.
Gout is characterized by recurring attacks in various joints of the body with the lower extremity joints being more commonly affected. The first metatarsophalangeal joint (podagra) is the most common joint involved with up to 50% of first time cases starting there, but the knee is commonly involved as well. Gout presents as polyarthritis in 10% of new cases. The attacks begin abruptly and reach maximum intensity within 8-12 hours. The joints are red, hot, and exquisitely tender; even a bed sheet on the swollen joint is uncomfortable. If left untreated, the first attacks usually resolve spontaneously in less than 2 weeks. Gout is slightly more common in blacks then whites, and is more common in men then in women. Usually uric acid levels are elevated for 20 years before an attack appears. Attacks are most common on the 4th to 6th decades and are rare in younger patients.
Gout is caused by the presence of urate crystals in the synovial fluid and soft tissue. Although the presence of urate crystals in the soft and synovial tissues is a prerequisite for a gouty attack, the fact that urate crystals can also be found in synovial fluid in the absence of joint inflammation suggests that the mere presence of intrasynovial urate crystals is not sufficient to cause flares of gouty arthritis. A gout attack may be triggered by either a release of uncoated crystals (eg, due to partial dissolution of a microtophus caused by changing serum urate levels) or precipitation of crystals in a supersaturated microenvironment.
Gouty attacks of the knee can eventually lead to degenerative changes if there is poor control of the disease with multiple recurrent attacks.
Diagnosis is definitively made by aspiration of joint fluid and examining the aspirate for urate crystals. Gouty attacks can mimic a septic joint, so aspiration and identification is almost always required. A history of previous attacks in other joints is necessary to obtain to help in determining if the etiology of the knee pain.
Imaging includes the use of plain x-rays to look for CPPD disease and any other bony abnormality which may be causing some of the symptoms. MRI and CT are never needed to help in diagnosing this disease.
Treatment options depend on severity of symptoms but includes medications such as indomethacin to help with inflammation, and allopurinol and colchicine to help with the reduction of uric acid. Surgery is usually not indicated unless there is an accompanying infection.
References
http://emedicine.medscape.com/article/329958-overview