Shoulder and upper arm muscle architecture.

Abstract

To examine the architecture of the shoulder and upper arm muscles and generate data that could serve as a guide for comparison, compatibility, and relative performance among these muscles for use in transfer. Eleven shoulder and arm muscles were dissected bilaterally in 5 fresh cadavers. Of these 110 potentially available muscles, 107 were suitable for evaluation and were grouped according to similarities in architecture. Resting muscle length, required excursion, muscle fiber length, pennation angle, and mass were determined. Physiologic cross-sectional area (PCSA) was then calculated from these parameters using a standard formula. Based on the gross appearance of muscle fiber orientation, the 11 muscles were subdivided into 3 groups. Required excursion was found to be less than fiber length in all muscles except for the teres major and middle deltoid with abduction. The middle deltoid muscle was found to have a short fiber length, complex multipennate structure, and high PCSA. Comparison showed the biceps and posterior deltoid to have fiber lengths greater than any portion of the triceps; however, neither demonstrated architectural features that would generate the force (represented by PCSA) determined for the combined triceps. Data presented in this study offer the opportunity for direct comparison of architectural features of select shoulder and arm musculature.