Dominic Stone
The infraspinatus muscle is a thick triangular muscle that is located in the shoulder joint. It is one of the four muscles of the rotator cuff, alongside the subscapularis, teres minor, and supraspinatus muscles. The infraspinatus muscle is responsible for the external rotation of the humerus and provides stability to the shoulder joint. It originates from the infraspinous fossa of the scapula and connects to the proximal humerus. The infraspinatus muscle is susceptible to tendinitis and atrophy and plays a crucial role in various shoulder movements, such as hitting overhead or carrying the arm backward.
| Characteristics | Values |
|---|---|
| Shape | Thick and triangular |
| Location | Shoulder joint |
| Function | External rotation of the arm, stabilization of the glenohumeral joint, and abduction of the inferior angle of the scapula |
| Innervation | Suprascapular nerve (C5 and C6) |
| Blood Supply | Suprascapular and circumflex scapular arteries |
| Lymphatic Drainage | Subscapular (posterior) nodes |
| Attachments | Medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus |
| Tendons | Blend with the fibrous capsule of the glenohumeral joint to form the rotator capsule |
| Susceptibility | Tendinitis due to overuse and misuse |
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What You'll Learn
The infraspinatus muscle is one of the four rotator cuff muscles
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 of the shoulder, along with the subscapularis, teres minor, and supraspinatus muscles. As part of the rotator cuff, the infraspinatus muscle plays a crucial role in stabilising the glenohumeral or shoulder joint.
The infraspinatus muscle arises from the infraspinous fossa of the scapula and connects to the proximal humerus. Specifically, it attaches medially to the infraspinous fossa and laterally to the middle facet of the greater tubercle of the humerus. The muscle fibres arise directly from the medial two-thirds of the infraspinous fossa, while the tendinous fibres come from the ridges of the fossa. The infraspinatus is also covered by the infraspinous fascia, which separates it from the teres major and teres minor muscles.
As a prime mover, the infraspinatus muscle acts as a powerful lateral rotator of the humerus. This function is essential for preloading the upper extremity in backward extension and external rotation on the shoulder joint, as seen in actions such as hitting overhead. Additionally, the infraspinatus assists in the external rotation of the arm and provides stability to the humerus head during arm movements. This stability is achieved through the rotator cuff muscles creating a concavity compression, preventing dislocation of the glenohumeral joint.
The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus. It receives its arterial blood supply from the suprascapular and circumflex scapular arteries. The infraspinatus is susceptible to tendinitis due to overuse and misuse, and trigger points in this muscle have been associated with referred pain to the middle and anterior deltoid regions.
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It is a thick, triangular muscle
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 of the shoulder, along with the subscapularis, teres minor, and supraspinatus muscles. As a rotator cuff muscle, the infraspinatus muscle's main function is to externally rotate the humerus and stabilize the glenohumeral or shoulder joint.
The infraspinatus muscle arises from the infraspinous fossa of the scapula and connects to the proximal humerus. Specifically, it attaches medially to the infraspinous fossa and laterally to the middle facet of the greater tubercle of the humerus. The muscle fibres arise directly from the medial two-thirds of the infraspinous fossa, while its tendinous fibres come from the ridges of the fossa. The infraspinatus muscle fibres course towards the shoulder joint, running almost parallel to the teres minor and major muscles.
The infraspinatus muscle is a powerful lateral rotator of the humerus, which is important for preloading the upper extremity in backward extension and external rotation on the shoulder joint. This action is seen in movements such as hitting overhead. Additionally, the infraspinatus muscle assists in the stabilization of the glenohumeral joint (GHJ) during arm movements. It works together with the teres minor muscle to prevent the upward displacement of the humeral head and impingement on the coracoid process.
The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus (C5 and C6). It receives its arterial blood supply from the suprascapular and circumflex scapular arteries. The infraspinatus muscle is susceptible to tendinitis due to overuse and misuse, which can result in shoulder and/or arm pain.
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It occupies the dorsal surface of the scapula
The infraspinatus muscle is a thick, triangular muscle that occupies the dorsal surface of the scapula. It is one of four muscles that comprise the rotator cuff of the shoulder, along with the subscapularis, teres minor, and supraspinatus muscles. The infraspinatus muscle is a powerful lateral rotator of the humerus, allowing for external rotation of the arm and providing stability to the shoulder joint.
The infraspinatus muscle arises from the infraspinous fossa of the scapula and connects to the proximal humerus. Specifically, it attaches medially to the infraspinous fossa and laterally to the middle facet of the greater tubercle of the humerus. The muscle fibres arise directly from the medial two-thirds of the infraspinous fossa, while the tendinous fibres come from the ridges of the fossa. The infraspinatus fossa is located on the posterior scapula, with the scapular spine dividing the posterior aspect of the scapula into the supraspinous and infraspinous fossae.
The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus. It receives its arterial blood supply from the suprascapular and circumflex scapular arteries. The infraspinatus is susceptible to tendinitis due to overuse or misuse, and it is often involved in rotator cuff tears.
The infraspinatus muscle works together with the teres minor muscle to stabilise the shoulder joint and prevent displacement of the humeral head. This is achieved through opposing the upward pull of the deltoid muscle during arm abduction. The infraspinatus and teres minor also act synergistically to rotate the head of the humerus outward during movements such as hitting overhead.
In summary, the infraspinatus muscle occupies the dorsal surface of the scapula and plays a crucial role in external rotation of the arm and stabilisation of the shoulder joint. It arises from the infraspinous fossa and connects to the humerus, receiving innervation from the suprascapular nerve. The infraspinatus muscle works in coordination with other muscles to maintain shoulder stability and enable smooth overhead movements.
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The infraspinatus is a prime mover and external rotator of the arm
The infraspinatus 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 of the shoulder, along with the subscapularis, teres minor, and supraspinatus muscles. The infraspinatus muscle is a prime mover and external rotator of the arm.
Acting as a prime mover, the infraspinatus muscle plays a crucial role in the lateral rotation of the humerus. This action is important for preloading the upper extremity in backward extension and external rotation at the shoulder joint. For example, when you hit something overhead, the infraspinatus muscle is contracted eccentrically to smoothen the upper extremity during the deceleration of powerful overhead movements.
The infraspinatus muscle also assists in the stabilisation of the glenohumeral joint, commonly known as the shoulder joint. This stabilisation is achieved through the rotator cuff muscles, which compress the humerus into the concavity of the glenoid fossa, preventing its dislocation. Additionally, the infraspinatus works together with the teres minor muscle to oppose the upward pull of the deltoid muscle, further stabilising the humeral head against the glenoid fossa.
The infraspinatus muscle originates from the infraspinous fossa of the scapula and connects to the proximal humerus. Specifically, it arises from the medial two-thirds of the infraspinous fossa by fleshy fibres and from the ridges on its surface by tendinous fibres. The fibres then converge into a tendon, which inserts into the middle facet of the greater tubercle of the humerus.
The infraspinatus muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus (C5 and C6). It receives its arterial blood supply from the suprascapular and circumflex scapular arteries.
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It is innervated by the suprascapular nerve
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 of the shoulder. The infraspinatus muscle is involved in the external rotation of the humerus and stabilisation of the shoulder joint.
The infraspinatus muscle is innervated by the suprascapular nerve. The nerve arises from the upper trunk of the brachial plexus, derived from roots C5 and C6. The suprascapular nerve innervates both the supraspinatus and infraspinatus muscles. These muscles are responsible for abducting and laterally rotating the arm.
The suprascapular nerve branches off the upper trunk of the brachial plexus and runs through the posterior triangle of the neck. It travels across the top of the scapula and passes through the scapular notch. The nerve then travels down the posterior scapula to innervate the supraspinatus muscle. Subsequently, it continues through the spinoglenoid notch to innervate the infraspinatus muscle.
The infraspinatus muscle is susceptible to tendinitis due to overuse and misuse. Atrophy or isolated weakness in the infraspinatus muscle may indicate compression of the suprascapular nerve near the scapular notch. This compression can be observed in overhead athletes and SLAP lesions. Myofascial release techniques may be employed to alleviate associated shoulder pain.
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Frequently asked questions
The infraspinatus muscle is a thick triangular muscle that occupies the dorsal surface of the scapula. It is one of the four rotator cuff muscles, alongside subscapularis, teres minor, and supraspinatus.
The main function of the infraspinatus muscle is to externally rotate the humerus and stabilize the shoulder joint. It also assists in carrying the arm backward.
The infraspinatus muscle is susceptible to tendinitis due to overuse and misuse, which can cause shoulder pain. Myofascial release techniques may help alleviate this pain.
