Quantitative evaluation of the posterior deltoid to triceps tendon transfer based on muscle architectural properties.

The architectural properties of the posterior deltoid muscle and the 3 heads of the triceps were measured using microdissection techniques to determine whether substitution of triceps function by the posterior deltoid is architecturally appropriate. Muscles from 10 fresh cadaver specimens were fixed by high-pressure perfusion using buffered formaldehyde. Muscle architectural properties, including pennation angle, fiber bundle length, sarcomere length, and physiologic cross-sectional area, were determined. Fiber bundle length varied significantly among the deltoid (123.1 +/- 7.8 mm), medial (64.5 +/- 3.8 mm), lateral (66.5 +/- 5.4 mm), and long (85.3 +/- 9.5) heads of the triceps. The physiologic cross-sectional area of the posterior deltoid was significantly less than the total triceps area and was predicted to provide only approximately 20% of the maximum isometric tension of the combined triceps heads. These data demonstrate that the long fibers of the posterior deltoid render it a very suitable transfer to provide elbow extension because of its tremendous excursion and also show why useful functional results seem relatively independent of posterior deltoid tension at the time of surgery.