Analysis of posterior deltoid function one year after surgical restoration of elbow extension

Purpose: The purpose of this study was to measure the extent and timing of elbow extension torque recovery after posterior deltoid-to-triceps tendon transfer. Methods: Elbow extension moment was measured in 40 limbs from 23 patients who underwent surgical restoration using the posterior deltoid-to-triceps tendon transfer at times ranging from 8 weeks to 1 year after surgery. For comparison purposes, elbow extension moment also was measured in healthy controls and persons with C7 spinal cord injuries. Results: Maximum extension moment was 5.89 ± 0.24 Nm (mean ± standard error of mean, n = 40), which corresponds to approximately 65% of the predicted posterior deltoid force and provided an adequate moment to oppose gravity. Based on the shape of the moment-joint angle curve and using a biomechanical model, it was predicted that posterior deltoid was inserted at a relatively short muscle length of 123.1 mm and thus operated exclusively on the ascending limb of the length-tension relationship. Conclusions: These observations support an evolving model of muscle architecture in which connective tissue septa restrict muscle fiber elongation during surgical tensioning of the tendon transfer. This relatively short length would result in a significant force loss should any of the repair sites slip or stretch during rehabilitation. These data have implications for the reconstruction and rehabilitation of this patient population.