Chemical structure of uric acid<unk>  is a disorder of purine metabolism, and occurs when its final metabolite, uric acid, crystallizes in the form of monosodium urate, precipitating and forming deposits (tophi) in joints, on tendons, and in the surrounding tissues. Microscopic tophi may be walled off by a ring of proteins, which blocks interaction of the crystals with cells and therefore avoids inflammation. Naked crystals may break out of walled-off tophi due to minor physical damage to the joint, medical or surgical stress, or rapid changes in uric acid levels. When they break through the tophi, they trigger a local immune-mediated inflammatory reaction in macrophages, which is initiated by the NLRP3 inflammasome protein complex. Activation of the NLRP3 inflammasome recruits the enzyme caspase 1, which converts pro-interleukin 1β into active interleukin 1β, one of the key proteins in the inflammatory cascade. An evolutionary loss of urate oxidase (uricase), which breaks down uric acid, in humans and higher primates has made this condition common. The triggers for precipitation of uric acid are not well understood. While it may crystallize at normal levels, it is more likely to do so as levels increase. Other triggers believed to be important in acute episodes of arthritis include cool temperatures, rapid changes in uric acid levels, acidosis, articular hydration and extracellular matrix proteins. The increased precipitation at low temperatures partly explains why the joints in the feet are most commonly affected. Rapid changes in uric acid may occur due to factors including trauma, surgery, chemotherapy and diuretics. The starting or increasing of urate-lowering medications can lead to an acute attack of<unk>  with febuxostat of a particularly high risk. Calcium channel blockers and losartan are associated with a lower risk of<unk>  compared to other medications for hypertension.
Gout
Septic arthritis
Greyout
Rheumatoid arthritis
Blackout 
Calcium pyrophosphate dihydrate crystal deposition disease
Barefoot
Alkaptonuria