Simulation of distal tendon transfer of the biceps brachii and the brachialis muscles.

Rupture of the distal tendons of the biceps brachii and the brachialis often consists of a clean avulsion of the end of the tendons from their tuberosities. In most of the reattachment procedures these tendons are reinserted to the same tuberosities. The purpose of this study was to examine the kinetic activity in the upper limb when the insertion locations of the two prime elbow flexors are altered. The right upper limb was modeled as a two-bar linkage moving in the vertical plane of the scapula. Our Hill-type musculo-tendon actuation system was modeled in terms of five muscles moving in three-dimensional space. The prime elbow flexors, i.e. the biceps brachii and the brachialis, were excited maximally, while the other muscles were left passive and were included as such in the analysis. The limb kinetics was studied in four different insertion locations of the biceps brachii and the brachialis. Data on the elbow kinematics, the muscle tensions histories, the muscle length-tension and velocity-tension relationships and the joint constraint forces were produced. The results indicate that when the new insertions of the biceps brachii and the brachialis are located further away from the elbow joint axis, the moments of these muscles about the joint axis increase. However, the shortening velocities of these muscles are increased as well, which results in a reduced tension. In addition, the magnitudes of the compressive force, the tangential forces and the torsional and bending moments are reduced. These results suggest that, whenever surgically possible, reinsertion of ruptured distal tendons of the biceps brachii and the brachialis more distally to the location of their tuberosities should be beneficial.