Infraspinatus

Original Editor - Wendy Walker

Lead Editors - Kate Sampson, Kim Jackson, Wendy Walker, Lilian Ashraf, Aya Alhindi, 127.0.0.1, Oyemi Sillo, WikiSysop, Naomi O'Reilly and George Prudden  

Description

A thick, triangular muscle; one of the 4 muscles which comprise the Rotator Cuff of the shoulder.

Origin

The infraspinatus fossa of scapula, with some fibres arising from the infraspinatous fascia which covers the muscle and separates it from Teres Major and Teres Minor.

Insertion

The posterior aspect of greater tuberosity of humerus, and the capsule of shoulder joint.

Nerve Supply

Suprascapular Nerve (C5 & C6)

Blood Supply

Suprascapular and circumflex scapular arteries.

Action

Infraspinatus is the main external rotator of the shoulder joint.

It assists in producing shoulder extension.

With the arm fixed, it abducts the inferior angle of the scapula. 

Function

It provides the primary muscle force for external rotation of the shoulder.

Along with the rest of the Rotator Cuff muscles it provides stability to the shoulder complex.

Clinical Relevance

Atrophy in the supraspinatus and infrapinatus muscles, usually indicates compression on the suprascapular never near the scapular notch, such compression can be seen in overhead athletes and SLAP lesions. While isolated weakness or atrophy in the infrapinatus muscle can be seen in suprascapular nerve compression in the spinoglenoid notch, compression of the nerve in the spinpglenoid notch is usually due to a ganglion cyst.

A study by Simons et al, described that infraspinatus muscle trigger points are associated with referred pain to the middle and anterior deltoid regions. Myofascial release techniques at the infraspinatus muscle may help shoulder pain.

Assessment

To evaluate the infraspinatus muscle the arm is placed in neutral abduction or adduction position with the elbow flexed 90 degrees. Lateral rotation of the shoulder is done against resistance, the test is positive if there is pain or weakness.