Mastering The Tongue Twister: Saying Infraspinatous Muscle

The infraspinatus muscle is a thick, triangular bipennate muscle with a fat stripe that divides it into top and bottom portions. It is one of the four muscles that make up the rotator cuff of the shoulder. The infraspinatus muscle is located on the dorsal surface of the scapula and works to abduct and laterally rotate the arm. It is closely related to the supraspinatus muscle, with which it is sometimes considered a single functional unit. Infraspinatus pain can range from mild strains to complete tears and can be treated with myofascial release techniques.

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Location and structure

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, along with the supraspinatus, teres minor, and subscapularis muscles. The rotator cuff muscles function to stabilize the shoulder joint and produce a wide range of arm motions.

The infraspinatus muscle arises from the medial two-thirds of the infraspinous fossa of the scapula, with strong muscle fibres originating from the medial three-quarters of the infraspinous fossa and tendinous fibres arising from the ridges of the fossa. The infraspinous fossa is found 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 covered by the infraspinous fascia, which separates it from the teres major and teres minor muscles.

From these origin points, the fibres of the infraspinatus muscle converge into a narrow tendon at the superolateral edge of the scapula. The tendon crosses the posterior side of the shoulder and inserts into the middle impression of the greater tubercle of the humerus. The tendon of the infraspinatus muscle can sometimes be separated from the capsule of the shoulder joint by a bursa, which may communicate with the joint cavity.

The infraspinatus muscle is supplied by the suprascapular nerve (C5 and C6), which arises from the superior trunk of the brachial plexus and passes laterally through the posterior triangle of the neck and through the scapular notch on the superior border of the scapula. The suprascapular nerve provides innervation to both the infraspinatus and supraspinatus muscles. The infraspinatus muscle receives arterial blood supply from the suprascapular and circumflex scapular arteries.

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Function

The infraspinatus is a thick, triangular muscle that occupies the dorsal surface of the scapula, or, more specifically, the infraspinous fossa of the scapula. It is one of the four muscles that comprise the rotator cuff of the shoulder, along with the supraspinatus, teres minor, and subscapularis muscles. The mnemonic "SITS" is often used to remember these four muscles.

As part of the rotator cuff, the infraspinatus muscle's primary function is to externally rotate the humerus and stabilize the shoulder joint, or, more specifically, the glenohumeral joint. It also assists in shoulder extension and provides the primary muscle force for external rotation of the shoulder. When the arm is fixed, it abducts the inferior angle of the scapula, a movement known as scaption, which increases the mobility of the scapula and assists the other shoulder muscles in allowing for full shoulder abduction.

The infraspinatus also works together with the teres minor muscle to oppose the upward pull of the deltoid muscle and stabilize the humeral head against the glenoid fossa. The infraspinatus provides the posterior force, while the subscapular muscle provides the anterior force, allowing for a balance of forces that stabilizes the joint.

The infraspinatus is susceptible to rotator cuff tears, usually due to anterior dislocations of the shoulder. In the case of a tear, the humeral head will elevate partially out of the glenoid fossa, decreasing the efficiency of the deltoid muscles' abduction action.

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Evolution

The infraspinatus muscle is a thick, triangular muscle that occupies a significant portion of the infraspinatous fossa in the human body. It is one of the four muscles of the rotator cuff, with its main function being to externally rotate the humerus and stabilize the shoulder joint. The infraspinatus muscle lies on the dorsal surface of the scapula, deep to the trapezius and parts of the deltoid and latissimus dorsi muscles.

The evolution of the infraspinatus muscle can be traced back to late reptilians and early mammals, where the muscle structure underwent a dorsal displacement. Over time, most of its components evolved into the pectoralis major, while some fibers attached to the scapula and gave rise to the supraspinatus, infraspinatus, and parts of the subscapularis.

In human anatomy, the infraspinatus muscle plays a crucial role in shoulder joint motion and stability. It is closely associated with the supraspinatus muscle, with which it shares a functional unit due to their close anatomical proximity. The infraspinatus is frequently fused with the teres minor, another muscle of the rotator cuff.

The infraspinatus muscle is innervated by the suprascapular nerve, which also innervates the supraspinatus muscle. Atrophy or weakness in the infraspinatus muscle can be indicative of compression on the suprascapular nerve near the scapular notch, a condition commonly observed in overhead athletes and SLAP lesions.

The infraspinatus muscle is a bipennate muscle, meaning it has two heads or points of origin. Its fibers travel superolaterally and insert onto the middle facet of the greater tubercle of the humerus via a flat tendon. This tendon can sometimes be separated from the capsule of the shoulder joint by a bursa, which may communicate with the joint cavity.

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Related injuries and pain

The infraspinatus muscle is one of the four muscles that make up the rotator cuff, which stabilises and moves the shoulder. It lies on the dorsal surface of the scapula, deep to the trapezius, and parts of the deltoid and latissimus dorsi muscles. The infraspinatus muscle works to rotate the arm laterally.

Due to its function, infraspinatus pain is often caused by overuse or repetitive movements. This is especially common in painters, carpenters, swimmers, and baseball players. In a study of 126 patients, 31% had shoulder pain that originated from the infraspinatus muscle.

Infraspinatus pain can be caused by a pinched nerve. The suprascapular nerve, which innervates the infraspinatus, can be compressed or pinched due to a weakened infraspinatus muscle, trauma, overuse injuries, or other shoulder dysfunction. This condition is rare but may occur in swimmers or baseball players.

Another cause of infraspinatus pain is tendinitis, or tendonitis, which is inflammation of the tendons. This can lead to the tearing of tendon tissues and may occur in older adults with rotator cuff tendinitis. Tears can also happen gradually due to age-related degeneration or suddenly from a fall onto an outstretched arm, shoulder dislocation, or collarbone fracture.

Treatment for infraspinatus pain typically involves nonsurgical methods such as rest, icing, and stretching exercises. NSAIDs like ibuprofen can help relieve pain and reduce swelling. Steroid injections can also be used for temporary relief but should be done sparingly as they can damage the muscle over time. In more severe cases, surgery may be recommended.

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Pronunciation

The infraspinatus muscle is a muscle that occupies the infraspinous fossa of the scapula and is inserted into the greater tubercle of the humerus. It is involved in rotating the arm laterally.

The infraspinatus muscle is pronounced as follows:

• In-fra-sin-ay-tus: Start by emphasizing the first syllable, "in," and then give a slight emphasis on the third syllable, "sin." The final syllable, "tus," is pronounced with a soft "s" sound, similar to the word "puss." The "a" in the second syllable, "ay," is pronounced as in the word "day."
• Breaking down the syllables: in-fra-sin-ay-tus
• In: Emphasize this syllable.
• Fra: Slightly reduce the emphasis but maintain a smooth flow.
• Sin: Emphasize this syllable slightly less than the first.
• Ay: Pronounce this syllable with the "a" sound as in "day."
• Tus: Finish with a soft "s" sound, similar to "puss."
• Practice and tips:
• Practice the word by breaking it down into its syllables and then gradually combining them.
• Emphasize the first and third syllables slightly more than the others.
• Focus on the "ay" sound in the third syllable to ensure clear pronunciation.
• Remember to end with a soft "s" sound for "tus."
• Repeat the word slowly at first and then increase your speed as you become more comfortable.
• Record and compare:
• Record yourself saying the word and play it back to check your pronunciation. Online tools and apps often provide this feature.
• Compare your pronunciation with audio examples provided by dictionaries or pronunciation websites. For example, Cambridge Dictionary offers British English pronunciations.
• Repeat this process to refine your pronunciation and make it more accurate over time.
• Related terms:
• The infraspinatus muscle is sometimes referred to as the "infraspinatus" or the "infraspinatus cuff."
• When discussing the anatomical region, it may be referred to as the "infraspinous fossa" or the "infraspinatous fossa of the scapula."
• Related muscles include the supraspinatus, teres minor and major, and the subscapularis.

Frequently asked questions