Update of the physiology and biomechanics of tendon transfer surgery.

Tendon transfer surgery has evolved over the past decade. Unique muscle properties have been elucidated in terms of potential force generation, excursion, and metabolic properties. The choice of an appropriate donor muscle is becoming more of a science than an art. The measurement of sarcomere length has progressed from the laboratory into surgery. Methods of tendon coaptation have advanced to allow early mobilization. This article reviews recent advances in our understanding of tendon transfer surgery of the hand and upper extremity.