The relationship between the innervation pattern of the suprascapular nerve (SSN) and the muscle architecture of supraspinatus has not been thoroughly investigated. The supraspinatus is composed of two architecturally distinct regions: anterior and posterior. Each of these regions is further subdivided into three parts: superficial, middle and deep. The purpose of this study was to investigate the course of the SSN throughout the volume of supraspinatus and to relate the intramuscular branches to the distinct regions and parts of the supraspinatus. The SSN was dissected in thirty formalin embalmed cadaveric specimens and digitized throughout the muscle volume in six of those specimens. The digitized data were modeled using Autodesk(®) Maya(®) 2011. The three-dimensional (3D) models were used to relate the intramuscular innervation pattern to the muscle and tendon architecture defined by Kim et al. (2007, Clin Anat 20:648-655). The SSN bifurcated into two main trunks: medial and lateral. All parts of the anterior region were predominantly innervated by the medial trunk and its proximal and medial branches, whereas all parts of the posterior region predominantly by the lateral trunk and its posterolateral and/or posteromedial branches. The posterior region also received innervation from the proximal branch of the medial trunk in half of the specimens. These findings provide evidence that the anterior and posterior regions are distinct with respect to their innervation. The 3D map of the innervation pattern will aid in planning future clinical studies investigating muscle activation patterns and provide insight into possible injury of the nerve with supraspinatus pathology and surgical techniques.

Neuromuscular partitioning is important in defining functional differences within a muscle volume. It has been shown that individual neuromuscular partitions may be differentially affected in pathology. Neuromuscular partitions are defined by independent innervation and architectural differences. Infraspinatus (IS) is a functionally important rotator cuff muscle where neuromuscular partitioning has not been well studied. The purpose is to investigate the intramuscular innervation patterns of IS. In this pilot study, 5 formalin‐embalmed cadaveric have been dissected, digitized, and modeled to date. The suprascapular nerve (SSN) was digitized sequentially in short segments and the data was modeled using Autodesk® Maya®2012. The models were used to document the intramuscular innervation patterns/neuromuscular partitions. The SSN enters IS at the spinoglenoid notch as 1–3 nerves. In three specimens, one nerve entered the IS belly and divided into 3 main branches: (1) a superior branch (br) to superior part of the muscle belly; (2) a lateral br to upper inferior belly; (3) middle br to middle and lower inferior bellies. When SSN enters as 2–3 branches, a separate lateral and/or superior branch enter their respective regions. These results provide a detailed mapping of the intramuscular innervation of IS, providing evidence of neuromuscular partitioning within the IS muscle belly.

Muscle architecture, the arrangement of fibre bundles within the muscle volume, has important functional implications. Previous studies of infraspinatus (IS) muscle architecture have focused on dissection and photography of the superficial muscle layers rather than a volumetric analysis. The aim of this study was to develop a methodology to quantify the architectural parameters of the fibre bundles throughout the volume of IS. As a prototype, one formalin‐embalmed cadaveric specimen was used. The IS was exposed and each fibre bundle was meticulously dissected and digitized from end to end. The digitized data was imported and a 3D model of the fibre bundle architecture, as in situ, was constructed in Autodesk® Maya®2012. Architectural parameters including fibre bundle length (FBL), pennation angle (PA), and physiological cross sectional area (PCSA) were computed. Based on the architectural parameters, muscular partitioning was determined. This technique successfully captured IS architecture throughout its volume. The IS was found to consist of 2 architecturally distinct regions, superior and inferior. The average measures for the superior and inferior regions were respectively: FBL 115.3mm; PA 22.2°; PCSA 180.3mm2 and FBL 84.9 mm; PA 15.9°; PCSA 550.5 mm2. The results suggest that there is muscular partitioning of the IS. This methodology will form the basis of a continuing study to understand detailed IS architecture at the fibre bundle level.