Changes of elbow muscle moment arms after total elbow arthroplasty

The changes of muscle moment arms on the elbow during simulated active motion were calculated from the simultaneous kinematic and tendon excursion in six cadaver specimens. The results after four different Coonrad-Morrey total elbow arthroplasty positions of implantation were compared with those of the intact elbow. With optimal total elbow arthroplasty implantation, the general pattern of change of the muscle moment arms with elbow flexion resembled that of the intact elbow, but with increased flexor dominance over the extensors with elbow flexion. No significant modification of the muscle moment arms was related to the changes of positioning of the implants, except with 60° elbow flexion, a slight increase of the brachialis muscle moment arms with distal placement of the humeral component. The malplacements of the humeral component in varus/valgus or in internal/external rotation were found to significantly affect the muscle moment arms.