Anatomical structure and nerve branching pattern of the human infraspinatus muscle.

The function of the infraspinatus muscle, critical to rotator cuff function, is dependent upon the muscle's structure and innervation pattern. The morphology of the infraspinatus muscle has been inconsistently described in the literature. Additionally, the branching pattern of the suprascapular nerve in the infraspinous fossa has not been addressed in the literature. The purposes of this study were to determine: the arrangement of the infraspinatus muscle bellies; the branching patterns of the suprascapular nerve to the infraspinatus muscle; if the infraspinatus muscle was composed the neuromuscular compartments. Forty-eight infraspinatus muscles from 24 embalmed cadavers were studied using standard dissection techniques to determine morphological characteristics and innervation patterns. Results demonstrated that the infraspinatus muscles were comprised of three separate muscular partitions with each partition residing in a thin fascial compartment but all residing deep to the posterior scapular fascia. A first order suprascapular nerve branch was present in 91.6% of superior, 100% of middle, and 70.8% of inferior partitions. A first order nerve was present in all 3 muscular compartments of the same infraspinatus muscle in 62.5% of cases. Second order nerve branches were present in 8.3% of superior, 0% of middle, and 29.2% of inferior partitions. These findings help to determine a more complete and accurate understanding of the structure of the infraspinatus muscle. A better understanding of its structure could lead to a better understanding of the function of the muscle. Such information will enable more effective rehabilitation strategies for injuries involving the infraspinatus component of the rotator cuff.