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The subscapularis muscle is a rotator cuff muscle that is responsible for the internal rotation of the arm and stabilization of the shoulder joint. The upper subscapular nerve, which stems from the superior cord of the brachial plexus, innervates the upper portion of the subscapularis muscle. The lower subscapular nerve, which comes from the posterior cord of the brachial plexus, innervates the lower portion of the subscapularis muscle. The subscapular nerves are a group of nerves that originate from the posterior cord of the brachial plexus and innervate the muscles that move the scapula.
| Characteristics | Values |
|---|---|
| Nerve Innervation | Upper and lower subscapular nerves |
| Nerve Origin | Posterior cord of the brachial plexus |
| Upper Subscapular Nerve | Innervates the upper portion of the subscapularis muscle |
| Middle Subscapular Nerve | Thoracodorsal nerve, innervates the latissimus dorsi muscle |
| Lower Subscapular Nerve | Inserts into the lower portion of the subscapularis muscle and the teres major |
| Function | Internal rotation of the arm and stabilization of the shoulder joint |
| Blood Supply | Branches of the subclavian artery |
| Risk | Iatrogenic injury during surgical procedures |
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What You'll Learn
Upper and lower subscapular nerves
The subscapularis muscle is innervated by the upper and lower subscapular nerves, which originate from the posterior cord of the brachial plexus. The upper subscapular nerve innervates the upper portion of the subscapularis muscle, while the lower subscapular nerve has two branches: one that inserts into the lower portion of the subscapularis muscle and another that inserts into the teres major.
The subscapularis muscle is a rotator cuff muscle that is responsible for the internal rotation of the arm and stabilization of the shoulder joint. It forms the majority of the posterior wall of the axilla and is one of four muscles of the rotator cuff, along with supraspinatus, infraspinatus, and teres minor. These muscles work together to stabilize and steer the humeral head within the glenoid cavity during movements of the upper limb.
The brachial plexus is formed by the ventral rami of the lower four cervical and upper thoracic nerve roots. These ventral rami fuse to form an upper, middle, and lower trunk, which then split into anterior and posterior divisions and subsequently into three cords: medial, lateral, and posterior. The subscapular nerves originate from the posterior cord.
Variations in the innervation of the subscapularis muscle have been observed, with some individuals having accessory upper or lower subscapular nerves. These accessory nerves are important to consider during surgical procedures, nerve blocks, and imaging. The subscapularis muscle also participates in the formation of three intermuscular axillary spaces: the quadrangular space, upper triangular space, and lower triangular space.
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Originating from the brachial plexus
The subscapularis muscle is innervated by two distinct nerve branches, the upper and lower subscapular nerves, which originate from the posterior cord of the brachial plexus. The brachial plexus is formed by the ventral rami of the lower four cervical nerve roots and the upper thoracic nerve roots. These ventral rami fuse to form an upper, middle, and lower trunk, which then split into anterior and posterior divisions. From here, they further divide into three cords: a medial, lateral, and posterior cord. The subscapular nerves arise from the posterior cord.
The upper subscapular nerve innervates the upper portion of the subscapularis muscle. It contains axons from the ventral rami of the C5 and C6 cervical spinal nerves. A lesion to the upper subscapular nerve can cause a reduced ability to medially rotate at the shoulder joint, but this function is supplemented by other muscles. The lower subscapular nerve innervates the lower portion of the subscapularis muscle and also has a branch that inserts into the teres major muscle.
The subscapularis muscle is a rotator cuff muscle that is responsible for the internal rotation of the arm and stabilization of the shoulder joint. It forms the majority of the posterior wall of the axilla, with the serratus anterior covering its superolateral part, and the coracobrachialis and biceps brachii muscles lying over its inferomedial part. The central part of the muscle is crossed by the cords of the brachial plexus and their branches, including the axillary nerve, artery, and vein.
The subscapularis muscle also participates in the formation of three intermuscular axillary spaces: the quadrangular space, upper triangular space, and lower triangular space. These spaces are traversed by various structures, including nerves, arteries, and veins. The upper and lower subscapular nerves that innervate the subscapularis muscle have a long course and are at risk of iatrogenic injury during certain surgical procedures, such as shoulder arthroplasty and exposure of the glenoid during a Latarjet procedure.
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Risk of injury during surgery
The subscapularis muscle is innervated by the upper and lower subscapular nerves, which originate from the posterior cord of the brachial plexus. The upper subscapular nerve innervates the upper portion of the subscapularis muscle, while the lower subscapular nerve has two branches, one of which inserts into the lower portion of the subscapularis muscle.
During surgical procedures involving the subscapularis muscle, there is a risk of injury to the nerves innervating the muscle. This is particularly true during axillary dissection procedures, such as lymphadenectomy, where the thoracodorsal nerve is exposed, and any originating subscapular nerves are at risk of iatrogenic injury. Therefore, the variability of the branching pattern of the subscapular nerve and the presence of accessory subscapular nerves should be carefully considered during preoperative planning to minimise the risk of nerve injury.
Additionally, when approaching the shoulder joint anteriorly, the subscapularis muscle may need to be tenotomized or split, which can further complicate the surgical approach and potentially increase the risk of nerve injury. In the event that the subscapularis muscle is inadvertently injured during surgery, it is crucial to repair the muscle promptly to prevent long-term functional deficits.
Furthermore, subscapularis tendon tears can occur after shoulder surgery, particularly when the subscapularis tendon is involved in the surgical procedure. In such cases, failure to adequately repair the subscapularis tendon can lead to poor outcomes, including enlargement of the tear and degeneration of the muscle quality. Therefore, it is essential to carefully assess the subscapularis tendon during surgery and ensure its proper repair to minimise the risk of postoperative complications.
Overall, the risk of injury to the subscapularis muscle and its associated nerves during surgery is a significant consideration. Careful surgical planning, an understanding of anatomical variations, and prompt repair of any inadvertent injuries are crucial to minimise the risk of complications and optimise patient outcomes.
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Accessory subscapular nerves
The subscapularis muscle is innervated by the upper and lower subscapular nerves, which originate from the posterior cord of the brachial plexus. However, accessory subscapular nerves have been observed in some individuals. Accessory nerves are additional nerves that deviate from the typical anatomical structure and supply the same region as the primary nerves.
In one study, accessory upper subscapular nerves were found in 9.7% of cases, with all three nerves identified as accessory upper subscapular nerves arising proximal to the thoracodorsal nerve. No accessory lower subscapular nerves were found in that particular study. However, other studies have reported the presence of accessory lower subscapular nerves originating from the axillary nerve or as a branch of it.
The presence of accessory subscapular nerves is important to consider during surgical procedures, nerve blocks, and imaging. For example, during axillary dissection, the thoracodorsal nerve is exposed, and any originating subscapular nerves are at risk of injury. Additionally, knowledge of the anatomical variation in the branching pattern of the brachial plexus is crucial during neck and axilla dissection.
Furthermore, the upper subscapular nerve's relation to nearby vessels is significant. The variation in its anatomical structure may lead to vessel impingement, resulting in ischemia and loss of functional anatomy in the muscle. This knowledge is essential for radiologists, surgeons, and anaesthesiologists, especially when dealing with clinical and surgical procedures in the axilla, scapular fracture, shoulder dislocation, and infraclavicular nerve blocks.
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Thoracodorsal nerve
The thoracodorsal nerve, also known as the middle or long subscapular nerve, is a motor nerve that arises from the C6 to C8 roots of the brachial plexus. It is a branch of the posterior cord of the brachial plexus and exits at the apex of the axilla. The thoracodorsal nerve is significant for its role in various nerve reconstruction procedures and its innervation of the latissimus dorsi muscle.
The thoracodorsal nerve runs posteriorly to the axillary vein as it descends through the axilla. It then joins the vascular pedicle of the latissimus dorsi muscle. The nerve is crucial during surgical procedures of the axilla, where it is used as a nerve graft. Its primary function is the motor innervation of the latissimus dorsi muscle, which is responsible for adduction of the shoulder joint.
The latissimus dorsi muscle is occasionally used for transplantation and augmentation of systole in cardiac failure. In these cases, the thoracodorsal nerve supply is preserved and transplanted along with the muscle. The nerve arises from the hypaxial motor column of the neural tube, supplying the latissimus dorsi muscle along with the thoracodorsal artery and vein.
The thoracodorsal nerve is located near the lymphatic vessels of the axilla, and its identification is essential during axillary lymph node dissection procedures to avoid injury. In about 40% of individuals, the axillary arch, which is derived from the latissimus dorsi muscle, receives innervation from the thoracodorsal nerve. Injury to this nerve can result in axillary arch dysfunction and nerve traction, potentially leading to thoracic outlet syndrome.
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Frequently asked questions
The subscapularis muscle is innervated by the upper and lower subscapular nerves.
The subscapular nerves originate from the posterior cord of the brachial plexus.
The subscapularis muscle is responsible for the internal rotation of the arm and stabilization of the shoulder joint.
Yes, the subscapularis muscle and its innervation are clinically significant during surgical procedures such as shoulder arthroplasty and the Latarjet procedure. Iatrogenic injuries to the subscapular nerves can occur, leading to potential abnormalities in muscle function.
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