Maximus Gage
The infraspinatus muscle is a thick, triangular muscle that is located at the back of the shoulder. It is one of the four muscles of the rotator cuff, the others being the supraspinatus, subscapularis, and teres minor. The infraspinatus muscle is attached to the top of the upper arm bone (humerus) and the shoulder blade (scapula). It plays a crucial role in the external rotation of the humerus and stabilization of the shoulder joint, allowing the shoulder to be the most mobile joint in the human body.
| Characteristics | Values |
|---|---|
| Type | Thick triangular muscle |
| Location | Back of the shoulder |
| Attachment | Shoulder blade (scapula) and upper arm bone (humerus) |
| Function | External rotation of the humerus, shoulder joint stability |
| Composition | Skeletal muscle, collagen, cross-striated muscles of mesodermal origin |
| Innervation | Suprascapular nerve (C5 and C6) |
| Arterial Supply | Suprascapular and circumflex scapular arteries |
| Lymphatic Drainage | Subscapular (posterior) nodes |
| Related Conditions/Injuries | Tendinitis, rotator cuff tears, myofascial pain syndrome, nerve compression |
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What You'll Learn
The infraspinatus muscle is one of the four rotator cuff muscles
The infraspinatus muscle is a powerful lateral rotator of the humerus, allowing for the abduction of the inferior angle of the scapula, termed scaption. Scaption increases the mobility of the scapula, assisting the other shoulder muscles in achieving full shoulder abduction. The infraspinatus muscle also acts on the head of the humerus, exerting a lateral or external rotational force. This force is synergistic with the teres minor muscle, which inserts on the inferior facet of the glenoid tubercle.
The infraspinatus muscle is involved in anterior-posterior force balance, providing the posterior force while the subscapular muscle provides the anterior force. This balance helps to stabilize the humeral head during shoulder abduction. When the infraspinatus muscle is deficient, such as in the case of a tear, the humeral head can partially dislocate from the glenoid fossa, reducing the efficiency of the deltoid muscles.
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 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.
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It is located at the back of the shoulder
The infraspinatus muscle is located at the back of the shoulder. It is one of four muscles that comprise the rotator cuff, along with the supraspinatus, subscapularis, and teres minor. The infraspinatus muscle is a thick, triangular muscle that occupies the majority of the dorsal surface of the scapula, or shoulder blade. It is covered by the infraspinous fascia, which separates it from the teres major and teres minor muscles.
The infraspinatus muscle originates from the medial three-quarters of the infraspinous fossa, which is found on the posterior scapula. The scapular spine divides the posterior aspect of the scapula into the supraspinous and infraspinous fossae. The infraspinatus muscle fibres arise directly from the medial two-thirds of the infraspinous fossa and from the ridges on its surface. These fibres converge to form a tendon, which attaches to the middle facet of the greater tubercle of the humerus, or upper arm bone.
The main function of the infraspinatus muscle is to externally rotate the humerus and stabilize the shoulder joint. It works together with the teres minor muscle to provide opposing forces that balance the movement of the shoulder. The infraspinatus abducts the arm at the glenohumeral joint and assists in carrying the arm backward. When the arm is fixed, the infraspinatus adducts the inferior angle of the scapula, making the scapula more mobile and allowing for full shoulder abduction.
In terms of innervation, the infraspinatus muscle is supplied by the suprascapular nerve (C5 and C6), which arises from the superior trunk of the brachial plexus. It receives arterial blood supply from the suprascapular and circumflex scapular arteries. Infraspinatus pain can be caused by mild strains or complete tears, with tears being more common in younger individuals due to sports injuries. Treatment for infraspinatus pain typically involves nonsurgical methods such as rest, ice, and stretching exercises.
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It is attached to the upper arm bone and shoulder blade
The infraspinatus muscle is a thick, triangular muscle that is located at the back of the shoulder. It is one of the four muscles that comprise the rotator cuff, along with the supraspinatus, subscapularis, and teres minor. The rotator cuff muscles work together to stabilize the shoulder joint, allowing it to move in multiple directions.
The infraspinatus muscle originates from the medial three-quarters of the infraspinous fossa, which is found on the posterior scapula. The scapula, or shoulder blade, is a large, flat bone located on the back of the shoulder. The infraspinatus muscle arises from the medial two-thirds of the infraspinous fossa, with strong muscle fibres connecting it to the proximal humerus, or upper arm bone.
The infraspinatus muscle's primary function is to externally rotate the humerus and stabilize the shoulder joint. It attaches medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus. This attachment allows the infraspinatus to exert a lateral or external rotational force on the head of the humerus.
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. When the arm is abducted, the infraspinatus works together with the teres minor muscle to oppose the upward pull of the deltoid muscle and stabilize the humeral head during shoulder abduction.
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The infraspinatus muscle helps to stabilise the shoulder joint
The infraspinatus muscle is a thick, triangular muscle located at the back of the shoulder. It is one of the four muscles that make up the rotator cuff, along with the supraspinatus, subscapularis, and teres minor. The rotator cuff muscles work together to stabilise the shoulder joint, allowing it to move in multiple directions.
The infraspinatus muscle originates from the infraspinous fossa of the scapula and connects to the proximal humerus. Specifically, it attaches medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus. The infraspinous fossa is found on the posterior scapula, and the infraspinatus muscle occupies the majority of this area.
As part of the rotator cuff, the infraspinatus muscle helps to stabilise the shoulder joint by holding the head of the humerus in the glenoid fossa of the scapula during its movements. This stabilisation prevents the dislocation of the humerus by translating forces. Additionally, the infraspinatus muscle is involved in the anterior-posterior force balance, providing the posterior force to balance the anterior force provided by the subscapular muscle.
The infraspinatus muscle also assists in the external rotation of the humerus. This external rotation is important in preloading the upper extremity in backward extension and external rotation on the shoulder joint, such as in overhead hitting actions. The infraspinatus muscle fibres course towards the shoulder joint almost parallel to the teres minor and major muscles, with which it also synergises to rotate the head of the humerus outward.
In summary, the infraspinatus muscle plays a crucial role in stabilising the shoulder joint by working in conjunction with the other rotator cuff muscles and providing balance to the forces acting on the shoulder. Its ability to aid in the external rotation of the humerus further contributes to its stabilising function and facilitates various shoulder movements.
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It is a thick, triangular muscle
The infraspinatus muscle is a thick, triangular muscle that is located at the back of the shoulder. It is one of the four muscles of the rotator cuff, alongside the subscapularis, teres minor, and supraspinatus muscles. The rotator cuff muscles work together to stabilize the glenohumeral, or shoulder joint, by holding the head of the humerus in the glenoid fossa of the scapula. This joint is the most mobile in the body, allowing the shoulder to move in many different directions.
The infraspinatus muscle occupies the majority of the dorsal surface of the scapula, arising from the medial two-thirds of the infraspinous fossa of the scapula. The infraspinatous fossa is found on the posterior scapula, and the infraspinatus muscle is covered by the infraspinatous fascia, which separates it from the teres major and teres minor. The fibres of the infraspinatus converge to a tendon, which glides over the lateral border of the spine of the scapula and passes across the posterior part of the capsule of the shoulder joint.
The infraspinatus muscle is a powerful lateral rotator of the humerus, and it is the main external rotator of the shoulder. It also assists in carrying the arm backward. The infraspinatus muscle is involved in anterior-posterior force balance, providing the posterior force to balance the anterior force provided by the subscapular muscle. This muscle is considered one functional unit with the supraspinatus due to their close anatomical relation and similar functions.
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Frequently asked questions
The infraspinatus muscle is located on the dorsal surface of the scapula. It is a thick triangular muscle that occupies the majority of the infraspinatous fossa.
The infraspinatus muscle is one of the four muscles of the rotator cuff. Its main function is to externally rotate the humerus and stabilize the shoulder joint.
The infraspinatus muscle is attached to the top of the upper arm bone (humerus) and the shoulder blade (scapula).
