Muscles rely on signals from nerves for movement and function. This article focuses on the Teres Major muscle and the specific nerve that innervates it, highlighting its role in shoulder movement and the clinical implications of nerve damage.
The Teres Major Muscle
The Teres Major is a thick muscle located in the lower part of the shoulder blade. It originates from the dorsal surface of the inferior angle of the scapula and inserts onto the medial lip of the intertubercular groove of the humerus, the upper arm bone.
While it works closely with other shoulder muscles, the Teres Major is distinct from the rotator cuff muscles because it does not attach to the shoulder joint capsule. Its functions at the glenohumeral (shoulder) joint include adduction (bringing the arm towards the body), internal or medial rotation (turning the arm inward), and assisting in extending the arm from a flexed position, such as pulling the arm backward. Due to its synergistic action with the latissimus dorsi muscle, it is sometimes referred to as “lat’s little helper”.
The Nerve Supplying the Teres Major
The Teres Major muscle receives its neural supply from the lower subscapular nerve. This nerve contains axons from the C5 and C6 cervical spinal nerves. It branches from the posterior cord of the brachial plexus, a complex network of nerves formed by the ventral rami of the lower four cervical and first thoracic spinal nerves.
After branching from the posterior cord, the lower subscapular nerve travels to its target muscles. In addition to innervating the Teres Major, this nerve also supplies the inferior portion of the subscapularis muscle, another muscle involved in shoulder movement. This neural connection enables the Teres Major’s ability to contract and perform its actions.
Clinical Importance of Teres Major Innervation
Understanding the innervation of the Teres Major muscle aids in diagnosing and managing various conditions affecting the shoulder and upper limb. Damage to the lower subscapular nerve can lead to weakness or impaired function of the Teres Major, impacting its movements. Patients might experience difficulty with daily activities that require these movements, like reaching into a back pocket or performing overhead tasks.
Injuries to the lower subscapular nerve often occur as part of brachial plexus injuries, which can result from trauma, such as motor vehicle accidents, falls onto the shoulder, or even repetitive stress in athletes. For instance, certain contact sports can lead to nerve stretching or compression, causing temporary or long-term issues. In some cases, damage to this nerve can result in muscle atrophy, where the muscle wastes away, or fatty replacement, which can be observed through imaging like MRI.
Knowledge of the Teres Major’s specific innervation guides clinicians in assessing the extent of nerve damage and planning appropriate rehabilitation strategies. Physical therapy aimed at strengthening the Teres Major and its synergistic muscles can help restore shoulder function following injury. Recognizing weakness patterns associated with lower subscapular nerve compromise allows for accurate diagnoses and targeted interventions, improving patient outcomes and shoulder recovery.