Biomechanic comparison of 3 tendon transfers for supination of the forearm

Flexion-pronation of the hand and the forearm is a common deformity when the upper extremity is affected by cerebral palsy. Solutions used to improve the pronation deformity and increase supination include transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis, pronator teres rerouting, and brachioradialis rerouting. The purpose of this study was to compare the biomechanic efficacy of these 3 tendon transfers in simulated supination in cadaveric forearms.

Ten fresh-frozen adult cadaveric above-elbow upper extremities were used. In each specimen the 3 tendon transfers were performed sequentially in random order and were loaded in increments of 4 N (1 lb) to a maximum of 36 N (8 lb). Measurements were recorded from the starting point of 90 degrees of pronation. Statistical analysis of the data included the Student t test with the Bonferoni correction.

For all transfers, supination increased in a nonlinear manner as the load was increased in a nonlinear manner. For the flexor carpi ulnaris transfer, the forearm reached its neutral position at a load of 9 N (2 lb). The forearm continued to rotate to up to 84 degrees of supination with 36 N (8 lb) of load. With the brachioradialis transfer, the forearm reached its neutral position at 13 N (3 lb) of load and continued to rotate to up to 33 degrees of supination with 36 N of load. With the pronator teres transfer, the forearm never reached the neutral position. Under a maximum load of 36 N, only 55 degrees of rotation from full pronation was obtained.

Transfer of the flexor carpi ulnaris to the extensor carpi radialis brevis proved to be the most effective transfer for producing supination in cadavers. The brachioradialis transfer was second best. The pronator teres rerouting was the least effective transfer in effecting simulated supination in this experiment.