An unreported infraspinatus muscle variation—two-headed infraspinatus minor muscle and three-headed fusion with the teres minor muscle

Abstract

The infraspinatus muscle is situated under the scapular spine in the infraspinous fossa and inserts into the greater tuberosity of the humerus. It is a component of a crucial shoulder muscle group, the rotator cuff. There are a few interesting additional muscles in the infraspinal region. In the literature they are called the infraspinatus superficialis, infraspinatus minor and infraspinatus accessory muscles. The infraspinatus minor muscle is described as a superficial muscle bundle running under the scapular spine. During routine anatomical dissection, an unreported variation of the infraspinatus minor muscle was found. It derived from the inferior surface of the scapular spine and the infraspinous fossa. It had two heads. The superior head inserted on the greater tuberosity of the humerus. The inferior head inserted on the tendinous part of the infraspinatus muscle. There was also an unusual fusion of the infraspinatus muscle with the teres minor muscle. In this paper we will discuss the anatomical and physiological relationships of this morphological variation.

Novel Muscle in Infraspinous Fossa

“…After passing the latter, the nerve innervated the muscle and the IS. However, in terms of shape, the muscle was directed orthogonally to the IS, and its direction also differed from other previously reported variations of the IS [10][11][12]. Rather, the direction was similar to that of the posterior part of the DELT.…”

Diagnosis of suprascapular nerve entrapment syndrome based on the infraspinatus muscle cross-sectional area on shoulder MRI

“…Its motor innervation is to the supraspinatus and infraspinatus muscles. [9][10][11] Traumatic injuries such as, clavicular fracture, scapular fracture, shoulder dislocation, the acromioclavicular joint, or proximal humerus fractures are common causes of nerve damage. Another cause of SNE include iatrogenic damages during exertional overload in physical or athletes laborers, surgical procedures, tuberous changes of this area.…”

Accessory infraspinatus muscle in a male cadaver: a case report

“…Other known variations of the infraspinatus muscle include fusions with the deltoid or teres minor muscle, partial division into two laminae overlying each other, division into two heads, and the occurrence of a partially separated infraspinatus minor muscle [4][5][6]9]. The infraspinatus minor muscle is described as a bundle of transverse muscle bers running underneath the scapular spine that is partially differentiated from the main body of infraspinatus and rejoins the main body in its tendinous portion [4][5][6]. The accessory infraspinatus muscle reported here is distinguished from other infraspinal variants on the basis that is fully differentiated from the underlying infraspinatus muscle, the overlying deltoid muscle, and the adjacent teres minor muscle from its origin to its insertion.…”

“…Other known variations of the infraspinatus muscle include fusions with the deltoid or teres minor muscle, partial division into two laminae overlying each other, division into two heads, and the occurrence of a partially separated infraspinatus minor muscle [4][5][6]9]. The infraspinatus minor muscle is described as a bundle of transverse muscle bers running underneath the scapular spine that is partially differentiated from the main body of infraspinatus and rejoins the main body in its tendinous portion [4][5][6].…”