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The infraspinatus is a thick triangular muscle that makes up a large part of the infraspinatous fossa of the scapula. It is one of the four muscles of the rotator cuff, along with the supraspinatus, teres minor, and subscapularis muscles. The rotator cuff muscles help form the glenohumeral joint, which is essential for shoulder joint motion and stability. The infraspinatus muscle's main functions are to externally rotate the humerus, stabilize the shoulder joint, and assist in abduction of the scapula. Injuries to the infraspinatus muscle can include tendinitis and tears, often due to repetitive overhead motions or acute trauma.
| Characteristics | Values |
|---|---|
| Shape | Thick triangular |
| Occupies | Infraspinous fossa of the scapula |
| Rotator cuff | One of the four muscles |
| Main function | Externally rotates the humerus and stabilizes the shoulder joint |
| Attachments | Medial – infraspinous fossa of the scapula, lateral – greater tubercle of the humerus |
| Innervation | Suprascapular nerve |
| Blood supply | Suprascapular artery |
| Injuries | Tendinitis, partial or full tendon tear |
| Stretching | Active stretching by grasping the elbow and tractioning the shoulder |
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What You'll Learn
The infraspinatus is a thick triangular muscle
The infraspinatus muscle has a crucial role in external rotation and stabilisation of the shoulder joint. It originates in the infraspinous fossa, which is located on the posterior scapula, and it inserts on the greater tubercle of the humerus. This muscle is responsible for providing a compressive and inferior force that stabilises the humeral head during overhead movements. It also assists in controlling the direction, degree, and quality of motion of the humeral head during upper extremity movements.
The infraspinatus is innervated by the suprascapular nerve, which tunnels through the spinoglenoid notch. Its blood supply typically comes from two large branches of the suprascapular artery. However, some studies have found that the subscapular artery supplies a significant portion of its circulation. The infraspinatus muscle can be stretched actively by grasping the elbow and tractioning the shoulder or by reaching backward towards the opposite shoulder blade.
The infraspinatus is susceptible to injuries such as tendinitis and tendon tears. Tendinitis is an inflammation of the tendon caused by repetitive overhead reaching, pushing, or lifting with outstretched arms. It commonly affects athletes who perform overhead activities. Tendon tears can be partial or full and may result from acute injuries or degeneration of the muscle over time. Maintaining proper body mechanics and posture is essential for preventing injuries to the infraspinatus muscle.
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It is part of the rotator cuff
The infraspinatus muscle is one of the four muscles of the rotator cuff, alongside the supraspinatus, teres minor, and subscapularis muscles. The rotator cuff is a group of four muscles that surround the shoulder, and each muscle plays a crucial role in maintaining the stability of the glenohumeral (GH) joint. The GH joint is formed by the humerus articulating with the glenoid fossa of the scapula, which is a bone that gives rise to the shoulder joint.
The infraspinatus muscle is a thick, triangular muscle that originates in the infraspinous fossa of the scapula and attaches laterally to the greater tubercle of the humerus. It is the main external rotator of the shoulder and is responsible for abducting and laterally rotating the arm. It also assists in carrying the arm backward and provides a compressive and inferior (downward) force that stabilizes the humeral head during overhead movements. This stabilization is achieved by counteracting the superior translatory force of the deltoid muscle.
The infraspinatus is involved in the anterior-posterior force balance, where it provides the posterior force, while the subscapular muscle provides the anterior force. This balance of forces is essential for the proper functioning of the shoulder joint. When the infraspinatus is injured, such as in the case of a torn tendon, the humeral head can elevate partially out of the glenoid fossa, leading to decreased efficiency in the deltoid muscles' abduction action.
Injuries to the infraspinatus muscle can result in pain and limited mobility in the shoulder. Tendinitis, or tendon inflammation, is a common issue, particularly in older adults with rotator cuff tendinitis, and can lead to tendon tears. Tears in the tendon can be partial or full and may result from acute injuries, degeneration, or repetitive overhead activities. Nonsurgical treatments, such as rest, ice, and stretching exercises, are often recommended for mild injuries. However, in more severe cases, surgery may be necessary.
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It is innervated by the suprascapular nerve
The infraspinatus muscle is a thick, triangular muscle that is one of the four muscles of the rotator cuff. It is a primary external rotator of the GH joint and is involved in movements such as opening a door. It also provides a compressive and inferior force that stabilizes the humeral head during overhead movements.
The infraspinatus muscle is innervated by the suprascapular nerve. This nerve is a branch of the superior trunk of the brachial plexus, specifically arising from the upper trunk formed by the union of the ventral rami of the cervical nerves C5 and C6. It is a mixed nerve, providing both sensory and motor supply to the suprascapular region.
The suprascapular nerve originates from the superior trunk of the brachial plexus and courses laterally, passing superior to the brachial plexus and through the posterior triangle of the neck. It then traverses the scapular notch and enters the supraspinous fossa, where it gives off branches to the supraspinatus muscle. The nerve continues through the greater scapular notch to reach the infraspinous fossa, where it provides terminal branches to the infraspinatus muscle.
The suprascapular nerve plays a crucial role in the function of the infraspinatus muscle. It provides motor innervation, enabling the muscle to contract and perform its role in external rotation and stabilization of the shoulder joint. The nerve also provides sensory supply to the glenohumeral and acromioclavicular joints, ensuring proper coordination and control during movements.
Suprascapular nerve entrapment syndrome can cause shoulder pain, muscle weakness, and localized muscular atrophy of the infraspinatus muscle. This condition arises when the nerve becomes entrapped and compressed within the suprascapular canal, leading to pain and impaired function in the infraspinatus and surrounding muscles.
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Its tendon passes posteriorly to the glenohumeral joint
The infraspinatus muscle is a thick triangular muscle that occupies the infraspinatous fossa of the scapula. It is one of the four muscles of the rotator cuff, along with the supraspinatus, teres minor, and subscapularis muscles. These muscles form the glenohumeral joint, aiding in shoulder joint motion and stability. The infraspinatus muscle's tendon passes posteriorly to the glenohumeral joint, inserting on the greater tubercle of the humerus. This bony landmark is a critical attachment point for the muscle, allowing it to exert its primary function as the external rotator of the glenohumeral joint.
The infraspinatus tendon's posterior passage is essential for the muscle's role in shoulder stability and movement. By attaching to the greater tubercle, the tendon helps to stabilise the humeral head in the glenoid fossa during upward and overhead movements of the arm. This stability is crucial for preventing injuries and ensuring optimal shoulder function. The tendon's passage also enables the infraspinatus to generate a compressive and inferior force, counteracting the superior translatory force of the deltoid muscle.
The infraspinatus tendon's attachment to the greater tubercle provides a strong connection for muscle contraction and relaxation during shoulder movements. This attachment point allows the infraspinatus to act as an external rotator of the humerus, assisting in abduction and lateral rotation of the arm. The tendon's posterior position facilitates this rotational motion, providing leverage and support for the arm's movement.
Furthermore, the posterior passage of the infraspinatus tendon contributes to the muscle's role in maintaining proper shoulder alignment. The tendon's attachment to the greater tubercle helps position the humeral head correctly within the glenoid fossa. This alignment is vital for the shoulder's stability and range of motion, ensuring smooth and efficient movement.
Injuries to the infraspinatus tendon, such as tendinitis or tears, can occur due to repetitive overhead motions or acute trauma. These injuries can lead to pain, weakness, and restricted shoulder movement. Therefore, the posterior passage of the infraspinatus tendon is crucial for maintaining the health and functionality of the glenohumeral joint, allowing for a full range of motion and stability during various activities.
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It is prone to tendinitis and tendon tears
The infraspinatus is one of the four muscles that make up the rotator cuff, along with the supraspinatus, subscapularis, and teres minor. It is a thick triangular muscle located at the back of the shoulder and is responsible for the movement and stability of the shoulder joint. The infraspinatus is also one of the two main external rotators of the humerus, accounting for up to 60% of the external rotation force. It assists in stabilizing the head of the humerus in the glenoid fossa during upward arm movements and provides a downward force that stabilizes the humeral head during overhead movements.
Due to its function in the shoulder, the infraspinatus is prone to tendinitis and tendon tears. Tendinitis, or tendonitis, is the inflammation of the tendon, which can result from repetitive overhead reaching, pushing, or lifting with outstretched arms. Athletes who perform overhead activities such as swimming, tennis, throwing, and gymnastics are at a higher risk of developing tendinitis. Tendinitis can cause pain deep in the shoulder joint and can lead to referred pain in other parts of the body.
Tears in the infraspinatus tendon can be partial or full and may result from acute injuries, such as a fall or direct blow, or the degeneration of the muscle over time. Similar to tendinitis, tendon tears are commonly associated with overhead activities that stress the shoulder joint, leading to instability and joint laxity. Patients with tendon tears experience pain during specific movements, such as sleeping, reaching overhead, or working on a computer. The treatment for tendon tears depends on the severity and can range from conservative care and physical therapy to surgical intervention in more severe cases.
To prevent injuries like tendinitis and tendon tears, it is essential to focus on proper body mechanics and posture, especially for those with sedentary jobs. Strengthening the infraspinatus muscle through exercises and stretching can also help improve its strength and flexibility, reducing the risk of injuries.
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Frequently asked questions
The infraspinatus muscle is a thick triangular muscle that occupies the infraspinous fossa of the scapula. It is one of the four muscles of the rotator cuff.
The infraspinatus muscle externally rotates the humerus and stabilizes the shoulder joint. It also assists in controlling the direction, degree, and quality of motion of the humeral head during upper extremity movements.
The most common injuries to the infraspinatus muscle are tendinitis (or tendinopathy) and a tear of the tendon. Tendinitis is an inflammation of the tendon that can result from repetitive overhead reaching, pushing, or lifting with outstretched arms.
The infraspinatus muscle can be stretched by grasping the elbow and tractioning the shoulder, with the elbow close to the chest, or by reaching backward to touch the opposite shoulder blade. Stretching under a hot shower directed at the muscle can also be beneficial.
The infraspinatus muscle is the primary external rotator of the GH joint (glenohumeral joint). It provides a compressive and inferior force that stabilizes the humeral head during overhead movements and counteracts the superior translatory force of the deltoid.
