An anatomical study of the transverse part of the infraspinatus muscle that is closely related with the supraspinatus muscle

Abstract

Background: Detailed anatomical information of the infraspinatus is important in order to discuss muscle function. The aim of this study was to investigate the morphology, histology and innervation of the infraspinatus muscle, in order to construct an anatomical basis for diagnoses and operative procedures.

Materials and methods: We used 51 shoulders without rotator cuff tears of 27 Japanese cadavers embalmed by 8% formalin. We observed the detailed morphology of the infraspinatus in 20 specimens macroscopically, and we also examined histologically in 7 specimens. In addition, we examined the innervation patterns of the supraspinatus and infraspinatus muscles in 24 specimens.

Results: The infraspinatus was composed of oblique and transverse parts in accordance with muscle fiber direction. Both parts had partially independent morphology, and the transverse part inserted into the main tendinous portion of the oblique part as a thin tendinous membrane. The transverse part was innervated by branches arising from the suprascapular nerve proximal to the spinoglenoid notch. The innervating branches ran on the superoposterior surface of the part, and entered the part from the posterior surface.

Conclusion: Although the transverse part is a part of the infraspinatus, according to its innervation, the transverse part might be closely related to the supraspinatus. The independent transverse part of the infraspinatus has not been noticed. When we diagnose and treat the rotator cuff region, it will be important to consider this part as well as the main oblique part of the muscle.

Level of evidence: Basic science study.