Resultant forces and angles of twist about the wrist after the ecrl to ecu tendon transfer

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Abstract
This paper describes an experimental investigation to determine the biomechanical efficacy of the extensor carpi radialis longus (ECRL) to extensor carpi ulnaris (ECU) tendon transfer procedure used in rheumatoid hand reconstruction. Six normal cadaver specimens were tested in an apparatus that measured (a) the forces acting on the hand to restrain it in seven characteristic wrist configurations, and (b) the amount of hand pronation/supination that occurred as a result of loads applied to the tendons of the six major wrist muscles. Each specimen was tested with the ECRL tendon intact, surgically released, and transferred to the insertion point of ECU. In the intact and transferred states, the ECRL tendon was loaded sequentially while the remaining five wrist tendons were subjected to equal constant loads. In all three experimental ECRL test states, forces were also applied to all intact wrist tendons in a manner designed to represent physiologic load sharing. When the ECRL tendon was loaded sequentially, the transfer resulted in the predictable increase in the radially directed restraining force and the predictable supination of the hand relative to the forearm. When all intact tendons were loaded physiologically, the transfer also resulted in an increase in the radially directed restraining force. Significant differences between test states occurred generally only between the intact and release states of the ECRL tendon and not between release and transferred states. The results confirm that the ECRL‐to‐ECU tendon transfer procedure leads to forces and displacements that tend to correct the undesired deformities commonly associated with advanced rheumatoid wrist disease; however, the similarity of results in release and transferred states indicates that the effectiveness of the procedure involves the loss of normal ECRL function rather than reinsertion into the ECU per se.