Wrist trauma can disrupt the ligamentous support between the carpal bones, leading to instability of the carpus and pain, loss of motion, and loss of function. The most common patter of wrist instability is scapholunate instability that results from a fall on the outstretched hand, possibly with twisting motion. The second most common carpal instability pattern is that between the triquetrum and the lunate, termed lunotriquetral instability. The AMA Guides to the Evaluation of Permanent Impairment directs physicians to use frontal and lateral roentgenographic projections of the wrist to evaluate carpal instabilities and to rate impairment as mild, moderate, or severe. Carpal height can be used to assess impairment. Carpal translation is a medial or lateral translation of the entire carpus on the forearm (radius and ulna). Arthritic changes also can impair wrist stability and are seen roentgenographically as loss of joint space in the wrist. The degree of carpal instability lies on a continuum of loss of carpal bone support and amount of collapse, and, although little absolute difference exists between a 28-degree radiolunate angle and a 31-degree measurement, these two measurements yield different impairment ratings. Also, some forms of instability (eg, dynamic carpal instability) appear roentgenographically if the wrist is stressed, and examiners have freedom to assign impairment without reproducible, objective measures.

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