The first four editions of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) used the range of motion (ROM) method and derived impairment percentages. This method is reliable and works well to rate finger joint injuries such as fractures or sprains that cause reduced finger joint ROM, but it frequently underestimates the functional difficulty (impairment) caused by tendon injuries that restrict the excursion of tendons. For this reason, the AMA Guides, Fifth Edition, introduced a second method to rate ROM in fingers, the total active motion (TAM) method. When an evaluator calculates the patient's impairment using the traditional method from the first four editions of the AMA Guides, the impairment percentage is likely to underestimate the patient's “real world” difficulty or function; the TAM method measures flexion when the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joints are in full simultaneous flexion, and it measures extension when all three joints are in full simultaneous extension. Based on an example and using the Combined Values Chart in the Fifth Edition and the traditional method (the only method allowed in the first four editions), one would assess a 16% impairment of the digit; using the TAM method now available in the Fifth Edition, the impairment is more appropriately estimated at 61%.

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