Logan Steele
The supraspinatus muscle is one of the four muscles that make up the rotator cuff, which is located in the supraspinatus fossa of the scapula. It is innervated by the suprascapular nerve, which is formed by the anterior rami of spinal nerves C5 and C6. The supraspinatus muscle helps to abduct the arm and stabilizes the humeral head in the shoulder joint. It is also often ruptured in sports involving sudden, forceful movements of the upper limb.
| Characteristics | Values |
|---|---|
| Innervated by | Suprascapular nerve |
| Suprascapular nerve formed by | Anterior rami of spinal nerves C5 and C6 |
| Suprascapular nerve root value | C5, C6 |
| Suprascapular nerve origin | Superior trunk of the brachial plexus |
| Supraspinatus muscle location | Deep to the trapezius muscle, superior to the spine of the scapula and infraspinatus muscle |
| Supraspinatus muscle shape | Small and triangular |
| Supraspinatus muscle function | Abducts the arm, stabilizes the humeral head in the shoulder joint, assists in abduction of the arm at the glenohumeral joint |
| Supraspinatus muscle tendon location | Passes laterally beneath the cover of the acromion |
| Supraspinatus muscle tendon insertion | Superior facet of the greater tubercle of the humerus |
| Supraspinatus muscle tendon inflammation | Can lead to supraspinatus tendinitis |
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What You'll Learn
The suprascapular nerve
The supraspinatus muscle is one of the four muscles that make up the rotator cuff, which is located in the supraspinous fossa of the scapula. The supraspinatus muscle assists in the abduction of the arm and stabilizes the humeral head in the shoulder joint.
The supraspinatus muscle is innervated by the suprascapular nerve, which branches off from the superior trunk of the brachial plexus. The brachial plexus is a network of nerves that originate from the spinal cord and supply the arm and shoulder. The suprascapular nerve specifically arises from the upper trunk of the brachial plexus, which is formed by the union of the ventral rami of the cervical nerves C5 and C6.
Suprascapular nerve entrapment syndrome or neuropathy is a rare condition that can cause pain, muscle weakness, and atrophy in the posterior shoulder region. It is usually caused by traumatic injury or compression of the suprascapular nerve, leading to weakened abduction and external rotation of the shoulder.
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Spinal nerves C5 and C6
The suprascapular nerve arises from the superior trunk of the brachial plexus, which is formed by the union of the ventral rami of the cervical nerves C5 and C6. It passes through the posterior triangle of the neck and the scapular notch on the superior border of the scapula. It then gives off branches to the supraspinatus muscle in the supraspinous fossa, before continuing to the infraspinatus muscle in the infraspinous fossa.
The suprascapular nerve provides motor innervation to the supraspinatus and infraspinatus muscles, as well as sensory innervation to the shoulder joint. This nerve can be damaged in fractures of the overlying clavicle, leading to reduced ability to abduct the arm.
A study examining the spinal root origins of the suprascapular nerve found that it was composed of the ventral rami of C5 and C6 in 76% of samples, with C5 being the largest contributor of nerve fibres. In some cases, the C4 and C6 nerves were also involved, but to a lesser extent.
The supraspinatus muscle plays an important role in shoulder function, and its tendon can become inflamed or ruptured, leading to conditions such as supraspinatus tendinitis and shoulder impingement syndrome.
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Brachial plexus
The supraspinatus muscle is innervated by the suprascapular nerve, which is formed by the anterior rami of spinal nerves C5 and C6. The suprascapular nerve is part of the brachial plexus, a network of nerve fibres that supplies the skin and musculature of the upper limb.
The brachial plexus is a somatic nerve plexus formed by the intercommunications among the ventral rami (roots) of the lower four cervical nerves (C5-C8) and the first thoracic nerve (T1). The plexus is responsible for the motor innervation of all the muscles of the upper extremity, except for the trapezius and levator scapula muscles. The brachial plexus also supplies all the cutaneous innervation of the upper limb, except for the area of the axilla.
The brachial plexus is typically composed of five roots, three trunks, six divisions, three cords, and terminal branches. The roots emerge from the transverse processes of the cervical vertebrae and unite to form the three trunks: the superior trunk (C5 and C6 roots), the middle trunk (C7), and the inferior trunk (C8 and T1 roots). The anterior divisions of the upper and middle trunks unite to form the lateral cord, which gives rise to the lateral pectoral nerve (C5, C6, and C7). This nerve supplies the pectoralis major muscle. The anterior division of the lower trunk forms the medial cord, which gives off the medial pectoral nerve (C8, T1), the medial brachial cutaneous nerve (T1), and the medial antebrachial cutaneous nerve (C8, T1). These nerves provide sensory innervation to the skin of the arm and forearm.
The posterior divisions of each of the three trunks unite to form the posterior cord. The upper (C7, C8) and lower (C5, C6) subscapular nerves descend behind the axillary artery to supply the subscapularis and teres major muscles. The brachial plexus also gives rise to other nerves, including the musculocutaneous nerve (C5 and C6) and the axillary nerve (C6-T1, with fibres from C5 in some individuals).
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Supraspinatus muscle function
The supraspinatus muscle is one of the four muscles that make up the rotator cuff, along with the infraspinatus, teres minor, and subscapularis muscles. It is the smallest and most superiorly located of these four muscles. The supraspinatus muscle originates from the supraspinous fossa, a shallow depression in the body of the scapula above its spine. The supraspinatus tendon passes laterally beneath the cover of the acromion and inserts into the superior facet of the greater tubercle of the humerus.
The primary function of the supraspinatus muscle is to abduct the arm and stabilize the humeral head in the shoulder joint. It assists in the abduction of the arm at the glenohumeral (shoulder) joint, particularly during the first 0 to 15 degrees of arm abduction, where it acts as the main agonist muscle. Beyond 15 degrees, the deltoid muscle becomes increasingly more effective at abducting the arm. Additionally, the supraspinatus muscle helps resist inferior gravitational forces placed on the shoulder joint due to the downward pull of the upper limb. It stabilizes the shoulder joint by keeping the head of the humerus firmly pressed medially against the glenoid fossa of the scapula.
The supraspinatus muscle is innervated by the suprascapular nerve, which arises from the superior trunk of the brachial plexus. The suprascapular nerve is formed by the anterior rami of spinal nerves C5 and C6, with contributions from C4 and C5 nerves as well. It passes through the suprascapular notch and supplies articular branches to the capsule of the shoulder joint. The suprascapular nerve provides motor innervation to the supraspinatus muscle, allowing it to contract and perform its function in arm abduction and stabilization.
The supraspinatus muscle is susceptible to injuries, particularly in sports involving sudden forceful movements of the upper limb. It is the most commonly ruptured rotator cuff muscle. The tendon of the supraspinatus muscle can also become inflamed, leading to supraspinatus tendinitis, which is often associated with shoulder impingement syndrome. Suprascapular nerve entrapment syndrome can also cause shoulder pain and localized muscular atrophy of the supraspinatus muscle, resulting in weakened abduction and external rotation of the shoulder.
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Supraspinatus impingement
The supraspinatus is a rotator cuff muscle that abducts the arm and stabilizes the humeral head in the shoulder joint. It is innervated by the suprascapular nerve, formed by the anterior rami of spinal nerves C5 and C6. The supraspinatus is the smallest of the four muscles that comprise the rotator cuff of the shoulder joint.
The cause of supraspinatus impingement is believed to be the narrowing of the subacromial space, which is normally 1.0 to 1.5 cm in width. This narrowing can be attributed to repetitive pathologic compression, degeneration, and fraying of the rotator cuff tendons. As a result, the humeral head applies a compressive force to either the rotator cuff, the subacromial bursa, or both structures, leading to pain and inflammation.
The diagnosis of supraspinatus impingement is primarily made through a patient's history and physical examination. Tests such as the Empty Can Test and the Full Can Test are commonly used to assess supraspinatus impingement or integrity. Magnetic resonance imaging (MRI) and ultrasound scans can also be utilized to visualize the rotator cuff tendons and detect any fluid, inflammation, or tears.
Treatment for supraspinatus impingement aims to reduce pain and restore function. Initial treatment is typically non-surgical, focusing on physical therapy exercises to strengthen the shoulder girdle and rotator cuff muscles, including the supraspinatus and infraspinatus. Pharmacological interventions may also be used to decrease inflammation. In cases where conservative management is ineffective, steroid injections or surgery to widen the space around the tendon may be considered.
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Frequently asked questions
The supraspinatus muscle is innervated by the suprascapular nerve, formed by the anterior rami of spinal nerves C5 and C6.
The suprascapular nerve is a mixed (sensory and motor) nerve that branches from the upper trunk of the brachial plexus.
The supraspinatus muscle is one of the four muscles that make up the rotator cuff. It helps to resist the inferior gravitational forces placed across the shoulder joint and stabilizes the glenohumeral (shoulder) joint during the movements of the upper limb.
