Biomechanical analysis of the brachioradialis as a donor in tendon transfer

Anatomic and biomechanical properties of the passive brachioradialis muscle were investigated to understand the limited excursion of this muscle seen during tendon transfer surgery. First, architectural measurements were perf ormed on three fiber bundles obtained from four regions of the brachioradia lis (10 specimens) chosen to represent the range of muscle fiber lengths ac ross the brachioradialis. Next, in separate specimens (eight specimens), pa ssive excursion was measured by securing the distal tendon stump to a servo motor. A constant load of 4.9 N was applied to the tendon, while the distal tendon was released from the surrounding tissue in 3-cm increments. Within the four regions studied, muscle fiber length varied significantly from 10 4.2 +/- 6.2 mm to 179.8 +/- 6.1 mm. As the brachioradialis was released, an average of 3 mm of mobility was obtained for each interval whereas for the succeeding three intervals, an average of 5.3 mm of mobility was obtained. This resulted in 22.2 +/- 2.3 mm of mobility when each specimen was fully released. These data show that there is no intrinsic muscle fiber length li mitation to excursion, but that excursion is limited by other intermuscular connections to adjacent connective tissue and other muscles.