Reduction of triceps muscle force after shortening of the distal humerus: a computational model.

Bone deficiency resulting in shortening of the distal humerus may occur after fractures, treatment of nonunions, or revision of total elbow arthroplasty. A biomechanical model of the triceps muscle and tendon was used to investigate the effect of distal humeral shortening on triceps force production. The analysis indicated that shortening of the distal humerus primarily influences the media head of the triceps, which contributes most to elbow extension strength in extended elbow positions. In a posture of 30 degrees elbow flexion, shortening the distal humerus by 1, 2, and 3 cm reduced the extension strength by 17%, 40%, and 63%, respectively. At 90 degrees of flexion, strength was reduced by 11%, 15%, and 21%, respectively. This result suggests that shortening the humerus by 1 cm may be well tolerated, but shortening by 2 or more cm may cause a significant reduction in triceps force. This would be particularly important in patients requiring terminal extension strength for weight bearing.