Unknown variant of the accessory subscapularis muscle?

Nicol Zielinska,R Shane Tubbs,Łukasz Olewnik,Marko Konschake

doi:10.1007/s12565-021-00633-8

Abstract

Acting in medial rotation of the arm, the subscapularis (SM) is the most powerful and largest muscle of the rotator cuff. It is morphologically variable, especially in the number of tendons, place of insertion, and number of bellies, and it is sometimes fused with another muscle. An accessory subscapularis muscle (ASM) is among the morphological variations of the SM, but it is a really rare variant. The present case describes a very rare ASM that is divided into proximal tendinous attachment, intermediate fleshy muscular belly and distal tendinous attachment. Its origin is located on the lateral border of the scapula, but some fibers are connected with the muscular part of the SM. Its distal attachment is fused with the capsule of shoulder joint, above the tendinous insertion of the SM. Such an arrangement allows for greater stabilization of the joint. Moreover, there is a possibility that it could be used during treatment of ruptured SM tendons.

Highlights

The most powerful and largest muscle of the rotator cuff is the subscapularis (SM), which acts in medial rotation of the arm (Bergman et al 2017)
The tendinous origin was located on the lateral border of the scapula, but some proximal fibers were connected to the muscular part of the SM
The accessory subscapularis muscle (ASM) consisted of proximal tendinous attachment, intermediate fleshy muscular belly and distal tendinous attachment

Summary

Introduction

The most powerful and largest muscle of the rotator cuff is the subscapularis (SM), which acts in medial rotation of the arm (Bergman et al 2017). The tendinous origin was located on the lateral border of the scapula, but some proximal fibers were connected to the muscular part of the SM It passed into the muscular part, and into distal attachment fused with the capsule of the shoulder joint above the insertion of the SM. We think that this structure, if present, could be helpful during operative treatment of a SM tendon rupture, so knowledge about it should be important for orthopedics specialists or surgeons. The distal attachment was fused with the medial part of the capsule of the shoulder joint, above the insertion of the SM.

Discussion

Conclusions