The lower subscapular nerve is one of the two subscapular nerves, the other being the upper subscapular nerve. Both are branches of the posterior cord of the brachial plexus. The lower subscapular nerve primarily provides motor innervation to the teres major and the lower part of the subscapularis muscle.
Structure
- Type: The lower subscapular nerve is primarily a motor nerve, and it innervates specific muscles in the scapular region.
- Origin: The nerve originates from the posterior cord of the brachial plexus, typically formed from nerve roots C5-C8.
- Branches: The lower subscapular nerve gives off branches to the lower part of the subscapularis muscle and the teres major muscle.
Location
- Origin and Course: Originating from the posterior cord of the brachial plexus, the lower subscapular nerve courses laterally and posteriorly within the axillary region.
- Axillary Region: The nerve travels in close proximity to other major nerves, including the axillary and radial nerves, as well as major vessels like the axillary artery and vein.
- Innervation Points: It travels toward the scapular region to innervate the lower part of the subscapularis muscle, situated on the inner side of the scapula in the subscapular fossa, and the teres major muscle, located on the outer aspect of the scapula near its lower edge.
Main Functions
The lower subscapular nerve serves specific functions related to the muscles it innervates, contributing to the range of movements and stability of the shoulder joint.
Motor Functions
- Subscapularis Muscle: The lower subscapular nerve provides innervation to the lower portion of the subscapularis muscle. This muscle is a vital part of the rotator cuff, which is crucial for stabilizing the shoulder joint. Specifically, the subscapularis muscle helps in internal rotation and adduction of the humerus, allowing actions such as reaching behind the back or throwing a ball.
- Teres Major Muscle: The nerve also innervates the teres major muscle. This muscle assists in adduction, extension, and internal rotation of the humerus. While it is not a part of the rotator cuff, it plays a significant role in shoulder and upper arm movements, working in tandem with other muscles like the latissimus dorsi.
Integrated Functions
- Shoulder Stability: By innervating a part of the subscapularis muscle, the lower subscapular nerve contributes to the overall stability of the shoulder joint, especially during movements that could potentially dislodge the head of the humerus from the glenoid fossa.
- Range of Motion: The muscles served by the lower subscapular nerve contribute to a broad range of arm movements. They facilitate actions such as pulling, lifting, and rotating the arm, essential for activities ranging from daily tasks to athletic performance.
- Synergistic Movements: The subscapularis and teres major muscles work in coordination with other muscles of the shoulder and upper arm. This synergy is important for the smooth and efficient movement of the upper limb.
Clinical Significance
The lower subscapular nerve holds significant clinical importance due to its role in shoulder functionality and stability.
Diagnostic Importance
- Shoulder Weakness and Pain: Dysfunction of the lower subscapular nerve could lead to specific weakness in the muscles it innervates, notably affecting internal rotation and adduction of the shoulder. This could be a diagnostic clue in evaluating shoulder pain and dysfunction.
- Rotator Cuff Assessment: While the subscapularis is primarily innervated by both the upper and lower subscapular nerves, dysfunction of the lower subscapular nerve could indicate an issue with this critical rotator cuff muscle, affecting shoulder stability.
Clinical Conditions
- Brachial Plexus Injuries: Since the nerve originates from the posterior cord of the brachial plexus, trauma to the brachial plexus could impact the function of the lower subscapular nerve.
- Surgical Risks: Surgeries involving the shoulder or axillary regions could potentially damage the lower subscapular nerve, leading to post-operative functional issues.
- Compression or Entrapment: Swelling or hypertrophy of surrounding tissues could potentially compress the nerve, leading to neuropathy and muscle weakness.
Therapeutic Interventions
- Physical Therapy: Exercises aimed at strengthening the innervated muscles and improving shoulder joint mobility can be beneficial in mild to moderate cases of nerve dysfunction.
- Nerve Decompression Surgery: In severe cases of entrapment, surgical intervention may be required to alleviate pressure on the nerve.
- Pain Management: Corticosteroid injections or analgesics may be used for managing chronic pain associated with lower subscapular nerve dysfunction.
