Logan Steele
The infraspinatus muscle is a thick, triangular muscle that is part of the rotator cuff. It originates from the infraspinous fossa of the scapula and connects to the proximal humerus. The infraspinatus muscle externally rotates the humerus and stabilizes the shoulder joint. The insertion point of the infraspinatus muscle is onto the greater tubercle of the humerus, with the tendon gliding over the lateral border of the spine of the scapula and passing across the posterior part of the shoulder joint.
| Characteristics | Values |
|---|---|
| Muscle Type | Thick, Triangular |
| Muscle Group | One of four rotator cuff muscles |
| Function | Externally rotates the humerus and protects the shoulder joint |
| Origin | Medial two-thirds of the infraspinous fossa |
| Insertion | Middle facet of the greater tubercle of the humerus |
| Innervation | Suprascapular Nerve (C5-C6) |
| Arterial Supply | Circumflex scapular and suprascapular arteries |
| Synergists | Teres minor and the deltoid |
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What You'll Learn
The infraspinatus is a thick, triangular muscle
The infraspinatus muscle arises from the infraspinous fossa of the scapula and connects it to the proximal humerus. The muscle fibres converge into a narrow tendon at the superolateral edge of the scapula. The tendon crosses the posterior side of the shoulder and inserts onto the middle impression of the greater tubercle of the humerus. The infraspinatus muscle is found deep to the trapezius, deltoid, and latissimus dorsi muscles.
The infraspinatus muscle is involved in the external rotation of the humerus and stabilisation of the glenohumeral, or shoulder, joint. It works together with the other rotator cuff muscles to hold the head of the humerus in the glenoid fossa of the scapula during its movements. The infraspinatus muscle also assists in carrying the arm backward and abducting the arm at the glenohumeral joint.
The infraspinatus muscle is susceptible to rotator cuff tears, which can occur due to anterior dislocations. It is also involved in anterior-posterior force balance, providing the posterior force while the subscapular muscle provides the anterior force. The infraspinatus muscle is innervated by the suprascapular nerve and supplied by the circumflex scapular and suprascapular arteries.
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It is one of the four rotator cuff muscles
The infraspinatus is one of the four muscles that make up the rotator cuff, along with the subscapularis, teres minor, and supraspinatus muscles. These muscles work together to stabilise the glenohumeral joint, or shoulder joint, by holding the head of the humerus in the glenoid fossa of the scapula. This prevents the dislocation of the humerus during arm movements.
The infraspinatus muscle is a thick, triangular muscle that occupies the majority of the dorsal surface of the scapula. It arises mostly from the infraspinous fossa of the scapula and connects to the proximal humerus. The muscle fibres converge to form a tendon, which inserts onto the middle facet of the greater tubercle of the humerus. This insertion point is located on the posterior part of the shoulder joint capsule.
As part of the rotator cuff muscles, the main function of the infraspinatus is to externally rotate the humerus and provide stability to the glenohumeral, or shoulder, joint. This muscle also assists in abduction and medial rotation of the arm at the glenohumeral joint. Additionally, the infraspinatus reinforces the capsule of the shoulder joint, providing protection to the shoulder.
The infraspinatus muscle receives its vascular supply from the suprascapular, subscapular, and posterior circumflex humeral arteries. It is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus. The infraspinatus is a powerful lateral rotator of the humerus, and this action is important in activities such as hitting overhead.
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Its insertion is at the middle facet of the glenoid tubercle
The infraspinatus is a thick, triangular muscle that occupies the dorsal surface of the scapula. It is one of the four muscles of the rotator cuff, alongside the supraspinatus, teres minor, and subscapularis. The infraspinatus muscle provides the mechanical link between the posterosuperior and anterior parts of the rotator cuff. It externally rotates the humerus and protects the shoulder joint.
The infraspinatus muscle's insertion at the middle facet of the glenoid tubercle allows it to exert a lateral or external rotational force. This force is synergistic with the teres minor, as the latter inserts on the inferior facet of the glenoid tubercle. The infraspinatus is frequently fused with the teres minor, and together, they rotate the head of the humerus outward and assist in carrying the arm backward.
The insertion of the infraspinatus onto the humerus is much larger than that of the supraspinatus, which explains why the infraspinatus is involved in rotator cuff tears as frequently as the supraspinatus. The infraspinatus is susceptible to rotator cuff tears, typically due to anterior dislocations. When the rotator cuff muscles are deficient, such as in the case of a torn infraspinatus tendon, the humeral head elevates partially out of the glenoid fossa, reducing the effectiveness of the deltoid muscles' abduction action.
The infraspinatus muscle's action on the shoulder is primarily through its function as a rotator cuff muscle, providing glenohumeral stability. It helps to hold the head of the humerus in the glenoid fossa of the scapula during its movements, thus stabilising the glenohumeral joint.
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The infraspinatus muscle's origin is the infraspinous 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's origin is the infraspinous fossa of the scapula. Specifically, it originates from the medial two-thirds of the infraspinous fossa, with some fibres arising from the deep surface of the infraspinous fascia, which covers the muscle and separates it from the teres major and minor muscles.
The infraspinatus muscle's primary function is to externally rotate the humerus and stabilise the shoulder joint. It provides the mechanical link between the posterosuperior and anterior parts of the rotator cuff. The muscle's fibres converge into a narrow tendon at the superolateral edge of the scapula, crossing the posterior side of the shoulder and inserting onto the middle impression of the greater tubercle of the humerus. This insertion point is larger than that of the supraspinatus muscle, which is why the infraspinatus is involved in rotator cuff tears as frequently as the supraspinatus.
The infraspinatus muscle also reinforces the capsule of the shoulder joint. It assists in shoulder extension and abducts the inferior angle of the scapula when the arm is fixed. Additionally, it provides the primary muscle force for external rotation of the shoulder. The infraspinatus muscle is innervated by the suprascapular nerve (C5-C6) and supplied by the circumflex scapular and suprascapular arteries.
The infraspinatus muscle can be tested by laterally rotating the arm at the glenohumeral joint against resistance, with the forearm held in a flexed position and the arm adducted. This movement isolates the infraspinatus and provides resistance to work the muscle. The infraspinatus is susceptible to rotator cuff tears, usually due to anterior dislocations, and subchondral cysts may be found at its insertion on the humeral head.
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It is involved in anterior-posterior force balance
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 rotator cuff muscles, along with the subscapularis, teres minor, and supraspinatus muscles. The infraspinatus muscle is involved in the anterior-posterior force balance, providing the posterior force to balance the movement of the shoulder.
The infraspinatus muscle originates from the medial two-thirds of the infraspinous fossa of the scapula. Its tendinous fibres arise from the ridges of the fossa, and it is covered by the infraspinous fascia, which separates it from the teres major and minor muscles. From these origin points, the fibres converge into a tendon that crosses the posterior side of the shoulder and inserts onto the greater tubercle of the humerus.
The infraspinatus muscle is involved in the external rotation of the humerus and the stabilisation of the glenohumeral or shoulder joint. It works together with the other rotator cuff muscles to hold the head of the humerus in the glenoid fossa of the scapula during its movements. This stabilisation mechanism prevents the dislocation of the humerus by translating forces and keeping the head of the humerus centralised within the glenoid cavity.
The infraspinatus muscle also assists in carrying the arm backward and abducting the inferior angle of the scapula when the arm is fixed. It provides the primary muscle force for external rotation of the shoulder. Along with the other rotator cuff muscles, it contributes to the overall stability of the shoulder complex.
The infraspinatus muscle receives its nerve supply from the suprascapular nerve and arterial blood supply from the suprascapular and circumflex scapular arteries. Atrophy or weakness in the infraspinatus muscle can be indicative of nerve compression or rotator cuff tears.
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Frequently asked questions
The infraspinatus muscle inserts onto the middle facet of the greater tubercle of the humerus.
The infraspinatus is a thick triangular muscle that is one of the four rotator cuff muscles.
The infraspinatus muscle originates from the medial two-thirds of the infraspinous fossa of the scapula.
The infraspinatus muscle externally rotates the humerus and stabilizes the shoulder joint.
