Infraspinatus

The infraspinatus is one of the four muscles of the rotator cuff in the shoulder. It lies in the infraspinous fossa of the scapula and plays a key role in stabilizing the glenohumeral joint while contributing to external rotation of the arm.

It originates from the infraspinous fossa and inserts into the middle facet of the greater tubercle of the humerus. The tendon may blend with the joint capsule and is positioned to transmit force to rotate the humerus outward.

The muscle is innervated by the suprascapular nerve, arising from the C5 and C6 nerve roots. Its arterial supply comes primarily from the suprascapular artery, with additional contributions from nearby vessels such as the circumflex scapular arteries.

Functionally, the infraspinatus is a major external rotator of the shoulder and helps stabilize the humeral head in the glenoid during arm movements. It works in concert with the teres minor as part of the external rotation force couple and contributes to shoulder joint stability during dynamic activity.

Clinical significance centers on rotator cuff pathology and nerve compression. Injuries can include tendinopathy, strain, or tears of the tendon, leading to weakness in external rotation. Suprascapular neuropathy can also affect function. Diagnosis is typically via clinical assessment and imaging, and treatment ranges from targeted physical therapy to surgical repair when indicated.