The shoulder is a complex and highly mobile joint, enabling a wide range of arm movements. This intricate system relies on the coordinated action of numerous muscles, each precisely controlled by specific nerves. Understanding which nerve supplies a particular muscle, such as the teres minor, offers insight into the mechanics of shoulder movement and the potential implications if that nerve is compromised.
Identifying the Nerve
The teres minor muscle receives its nerve supply from the axillary nerve. This nerve emerges from the posterior cord of the brachial plexus, a network of nerves originating from spinal nerve roots C5 and C6 in the neck. After branching from the brachial plexus, the axillary nerve travels behind the axillary artery and in front of the subscapularis muscle. It then passes through a confined anatomical space known as the quadrangular space, alongside the posterior circumflex humeral artery. This nerve directly innervates the teres minor, providing the sole neural pathway for its function, unlike some other shoulder muscles that might receive input from multiple nerves.
Understanding the Teres Minor Muscle
The teres minor muscle is a narrow, elongated component of the rotator cuff, a group of four muscles that surround the shoulder joint. It originates from the upper two-thirds of the lateral border of the scapula. From there, its fibers extend upward and laterally, inserting onto the inferior facet of the greater tubercle of the humerus. The teres minor helps to stabilize the ball-and-socket glenohumeral joint by assisting in holding the humeral head within the shallow glenoid cavity of the scapula. Its primary actions involve externally rotating the arm and assisting in adduction.
When the Nerve is Affected
Damage to the axillary nerve can significantly impair the teres minor muscle. Such injury can result from direct trauma, such as a shoulder dislocation or a fracture of the humerus. Compression of the nerve, for instance, in conditions like quadrangular space syndrome, or prolonged pressure from sources like crutches, can also lead to axillary nerve dysfunction. Individuals with an affected axillary nerve may experience weakness in external rotation of the arm and difficulty with overhead movements.
Symptoms can also include pain around the shoulder and a diminished sensation over the lateral aspect of the shoulder. Over time, prolonged nerve damage can lead to muscle atrophy. Initial management often involves rest and physical therapy to maintain joint flexibility and promote recovery. If natural recovery does not occur within several months, surgical intervention may be considered.