The upper subscapular nerve is one of the two subscapular nerves, along with the lower subscapular nerve. Both are branches of the posterior cord of the brachial plexus. The upper subscapular nerve primarily provides motor innervation to the upper part of the subscapularis muscle.
Structure:
- Type: The upper subscapular nerve is primarily a motor nerve. It innervates the upper portion of the subscapularis muscle, which is one of the rotator cuff muscles in the shoulder.
- Origin: It arises from the posterior cord of the brachial plexus, usually stemming from nerve roots C5 and C6.
- Branches: It is mainly a single branch that supplies the upper part of the subscapularis muscle.
Location
- Origin and Course: The nerve originates from the posterior cord of the brachial plexus within the axillary region (armpit).
- Pathway: The nerve courses laterally and posteriorly, running along the inner side of the scapula to reach the subscapularis muscle. It typically travels parallel or close to the lower subscapular nerve but terminates in the upper part of the subscapularis muscle.
- Innervation Point: The upper subscapular nerve innervates the upper part of the subscapularis muscle, which is situated on the anterior surface of the scapula in the subscapular fossa.
Functions
The upper subscapular nerve has a specific role in the functionality and stability of the shoulder joint, primarily through its innervation of the upper portion of the subscapularis muscle.
Motor Functions
The upper subscapular nerve innervates the upper part of the subscapularis muscle, which is one of the four rotator cuff muscles. The subscapularis muscle is crucial for internal rotation and adduction of the humerus at the shoulder joint. For example, this action is vital when you try to place your hand behind your back or throw a ball with an underhand motion.
Integrated Functions
Shoulder Stability: The subscapularis muscle, innervated in part by the upper subscapular nerve, is a critical element in the rotator cuff. This muscle complex provides stability to the glenohumeral joint, ensuring that the head of the humerus remains seated in the glenoid fossa, especially during upper limb movements that could otherwise dislocate it.
Range of Motion: The subscapularis muscle contributes to a broad range of arm movements, including internal rotation and adduction. These movements facilitate various daily tasks such as lifting objects, pushing doors, or any activity requiring the inward rotation of the arm.
Synergistic Actions: The subscapularis muscle works in synergy with other rotator cuff muscles and the deltoid for efficient and effective upper limb movements. The coordination is particularly important for activities that require a mix of strength, speed, and precision, such as throwing an object.
Clinical Significance
The upper subscapular nerve, which innervates the upper portion of the subscapularis muscle, has notable clinical significance, particularly in the context of shoulder function and stability.
Diagnostic Importance
Shoulder Dysfunction: The upper subscapular nerve plays a role in internal rotation and adduction of the shoulder. Dysfunction of this nerve may manifest as specific limitations in these movements, which can be a diagnostic clue in the context of shoulder pain and mobility issues.
Rotator Cuff Involvement: Since the subscapularis is a key component of the rotator cuff, assessing the function of the upper subscapular nerve may provide insights into rotator cuff health, particularly in cases of suspected injury or tear.
Clinical Conditions
- Brachial Plexus Injury: Given that the nerve originates from the posterior cord of the brachial plexus, it may be impacted in cases of brachial plexus injuries, leading to shoulder dysfunction.
- Nerve Entrapment: Although less common, localized compression or entrapment could potentially affect the upper subscapular nerve, leading to muscle weakness and atrophy.
- Surgical Risks: The nerve could be at risk during surgical procedures involving the axillary region or the posterior aspect of the shoulder, making anatomical understanding crucial for surgical planning.
Therapeutic Implications
- Rehabilitation: Physical therapy aimed at strengthening the subscapularis muscle can be effective in cases of mild dysfunction of the upper subscapular nerve.
- Surgical Intervention: In extreme cases, surgical decompression or nerve repair may be considered, especially if the nerve dysfunction is affecting the patient’s quality of life significantly.
- Pain Management: For chronic pain associated with nerve dysfunction, corticosteroid injections or other forms of pain management may be employed.
