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The infraspinatus muscle is a thick triangular muscle that occupies the dorsal surface of the scapula, a triangular, flat bone that serves as an attachment site for many muscles. The infraspinatus muscle is one of the four muscles of the rotator cuff, which functions to stabilize and produce movements in the shoulder joint. It originates from the infraspinous fossa of the scapula and wraps around the lateral proximal humerus to attach to the middle facet of the greater tubercle. The suprascapular nerve innervates the infraspinatus muscle, providing both motor and sensory innervation. This nerve arises from the upper trunk of the brachial plexus and supplies the shoulder joint. The infraspinatus muscle is involved in external rotation of the arm and works with other muscles to stabilize the shoulder joint.
| Characteristics | Values |
|---|---|
| Muscle name | Infraspinatus |
| Shape | Thick and triangular |
| Location | Dorsal surface of the scapula |
| Function | External rotation of the humerus, stabilization of the shoulder joint |
| Innervation | Suprascapular nerve |
| Arterial blood supply | Suprascapular and circumflex scapular arteries |
| Related conditions | Atrophy, contracture, rotator cuff tears |
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What You'll Learn
The infraspinatus muscle is one of the four rotator cuff muscles
The infraspinatus muscle is indeed one of the four muscles that make up the rotator cuff, along with the supraspinatus, teres minor, and subscapularis muscles. These muscles work together to provide stability and mobility to the shoulder joint, allowing a wide range of arm movements while keeping the head of the humerus centralised within the glenoid cavity.
The infraspinatus muscle is a thick, triangular muscle that occupies the majority of the dorsal surface of the scapula. It arises from the infraspinous fossa of the scapula and connects to the proximal humerus. The muscle fibres converge to form a tendon, which inserts into the middle facet of the greater tuberosity of the humerus. This tendon can sometimes be separated from the capsule of the shoulder joint by a bursa, which may communicate with the joint cavity.
As part of the rotator cuff, the main function of the infraspinatus muscle is the external rotation of the humerus, as well as the stabilisation of the shoulder joint. It works together with the teres minor muscle to rotate the head of the humerus outward and assist in carrying the arm backward. The infraspinatus muscle is also involved in abduction and adduction movements of the arm.
The infraspinatus muscle is innervated by the suprascapular nerve and receives its arterial blood supply from the suprascapular and circumflex scapular arteries. It is susceptible to injuries such as tendinitis and tears due to its involvement in shoulder movements and its close anatomical relation to the supraspinatus muscle.
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It externally rotates the humerus and stabilises the shoulder joint
The infraspinatus muscle is a thick triangular muscle that occupies the dorsal surface of the scapula, or shoulder blade. It is one of the four muscles of the rotator cuff, which is a group of muscles that originate from the scapula and attach to the humeral head. The other three rotator cuff muscles are the supraspinatus, subscapularis, and teres minor.
The main function of the infraspinatus muscle is to externally rotate the humerus and stabilize the shoulder joint. It does this by pulling the humeral head into the glenoid fossa, also known as the glenohumeral joint, which is the ball-and-socket joint of the shoulder. This joint has a wider range of motion than any other joint in the body, allowing for movements such as throwing a ball or reaching for an item on a shelf.
The infraspinatus muscle works together with the teres minor muscle to provide a wide range of arm motion while keeping the head of the humerus centralized within the glenoid cavity. This prevents dislocation by translating forces. Additionally, when the arm is abducted, the infraspinatus and teres minor work together to oppose the upward pull of the deltoid muscle and stabilize the humeral head against the glenoid fossa.
The infraspinatus muscle also assists in carrying the arm backward and is involved in powerful overhead movements, such as hitting overhead. It contracts eccentrically to smoothen the upper extremity during the deceleration of these movements.
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It originates in the infraspinatous fossa of the scapula
The infraspinatus muscle is a thick, triangular muscle that occupies the majority of the dorsal surface of the scapula. It is one of the four muscles of the rotator cuff, alongside the subscapularis, teres minor, and supraspinatus muscles. The infraspinatus muscle originates in the infraspinatous fossa of the scapula. Specifically, it arises from the medial two-thirds of the infraspinous fossa, with its tendinous fibres arising from the ridges on its surface.
The infraspinatus muscle is a powerful lateral rotator of the humerus. It acts to externally rotate the arm and stabilise the shoulder joint. This action is important in preloading the upper extremity in backward extension and external rotation on the shoulder joint, as seen in actions such as hitting overhead. The muscle contracts eccentrically to smoothen the upper extremity during the deceleration of powerful overhead movements.
The infraspinatus muscle fibres course towards the shoulder joint almost parallel to the teres minor and major muscles, separated from them by a thick fascia. As it approaches the shoulder joint, the infraspinatus may be separated from the neck of the scapula by the infraspinatus bursa, which can communicate with the shoulder joint cavity. The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus, receiving fibres from C5 and C6.
The suprascapular nerve is at risk during massive rotator cuff repairs, and literature has described the nerve as being very close to the operative field used in these repairs. Compression on the suprascapular nerve near the scapular notch can be seen in overhead athletes and SLAP lesions. Caution is needed during clinical procedures involving the infraspinatus muscle, as positioning the patient's arms in a particular way can cause the scapula to move laterally, exposing the lung.
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The suprascapular nerve innervates the infraspinatus muscle
The infraspinatus muscle is a thick, triangular muscle that makes up part of the rotator cuff of the shoulder. It originates from the infraspinous fossa of the scapula and wraps around the lateral proximal humerus to attach to the middle facet of the greater tubercle.
The suprascapular nerve is a branch of the superior trunk of the brachial plexus. It provides innervation to the infraspinatus and supraspinatus muscles. The nerve originates in the posterior triangle of the neck and runs laterally and downward, parallel to the belly of the omohyoid muscle, to the upper part of the scapula. It then passes through the suprascapular notch and into the supraspinous fossa, where it gives off branches to the supraspinatus muscle. The nerve continues through the spinoglenoid notch to the infraspinous fossa, where it terminates within the infraspinatus muscle, providing innervation.
The suprascapular nerve has both motor and sensory functions. The motor function involves providing innervation to the supraspinatus and infraspinatus muscles, allowing for abduction and external rotation of the arm. The sensory function involves providing innervation to the acromioclavicular and glenohumeral joints.
Injuries to the suprascapular nerve can result in pain and muscle weakness in the posterior shoulder region, affecting the abduction and external rotation of the shoulder. Atrophy of the infraspinatus muscle can indicate compression of the suprascapular nerve near the scapular notch, which can be seen in overhead athletes and SLAP lesions.
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It is involved in rotator cuff tears
The infraspinatus muscle is a thick, triangular muscle that occupies the dorsal surface of the scapula. It is one of the four muscles that comprise the rotator cuff, the others being the subscapularis, teres minor, and supraspinatus muscles. The rotator cuff muscles form a functional musculotendinous unit that stabilizes and produces movements in the shoulder joint. The tendons of these muscles blend with the fibrous capsule of the glenohumeral joint to form a tendinous sleeve called the rotator capsule.
The infraspinatus muscle is involved in rotator cuff tears due to its close anatomical relation to the supraspinatus muscle. The supraspinatus tendon is the most common site of rotator cuff tears, but rotator cuff tears may also involve other tendons. The infraspinatus and supraspinatus muscles are considered one functional unit as they are separated only by the spine of the scapula. The infraspinatus muscle is also frequently fused with the teres minor, which is another muscle that can be affected by rotator cuff tears.
Rotator cuff tears can be partial or complete and can occur at any age, but the risk increases with age. By the age of 60, many individuals are likely to have some degree of rotator cuff tearing. While the exact cause of rotator cuff tears is unknown, they are associated with aging and repetitive stress on the shoulder. Activities that involve repetitive overhead motions, such as tennis, baseball, and weightlifting, can increase the risk of rotator cuff tears. Additionally, a lack of blood supply due to aging can impair the body's ability to repair tendon damage, making older individuals more susceptible to tears.
The treatment for rotator cuff tears aims to reduce pain and restore function. In most cases, non-surgical treatments such as rest, activity modification, anti-inflammatory medications, and physical therapy are effective in relieving pain and improving shoulder function. However, in some instances, surgery may be necessary to repair the tear and restore shoulder movement.
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Frequently asked questions
The infraspinatus muscle is found on the dorsal surface of the scapula, arising lateral and inferior from the supraspinatus muscle.
The infraspinatus muscle is one of the four rotator cuff muscles, along with the subscapularis, teres minor, and supraspinatus muscles. Its main function is to externally rotate the humerus and stabilize the shoulder joint.
The infraspinatus muscle is palpated by flat palpation perpendicular to the muscle fiber direction against the infraspinous fossa. The clinician assesses the muscle for taut bands with spot tenderness to identify MTrPs.
