From the Guidelines
The subscapularis muscle is innervated by the upper and lower subscapular nerves, which originate from the posterior cord of the brachial plexus, specifically arising from the C5 and C6 spinal nerve roots. The brachial plexus is formed from the C5 to T1 ventral rami, as described in the study by 1, which provides a comprehensive overview of plexopathy. The upper subscapular nerve primarily supplies the upper portion of the subscapularis muscle, while the lower subscapular nerve innervates the lower portion. This dual innervation ensures proper function of the subscapularis, which is a critical rotator cuff muscle responsible for internal rotation of the humerus and stabilization of the glenohumeral joint. Understanding this innervation pattern is important for clinicians when evaluating shoulder dysfunction, performing nerve blocks, or interpreting findings in patients with cervical radiculopathy, as damage to these nerve roots can lead to weakness in internal rotation of the shoulder and potential instability of the glenohumeral joint, as supported by the study 1. Key points to consider include:
- The brachial plexus is formed from the C5 to T1 ventral rami
- The subscapularis muscle is innervated by the upper and lower subscapular nerves
- The upper and lower subscapular nerves arise from the C5 and C6 spinal nerve roots
- Damage to these nerve roots can lead to weakness in internal rotation of the shoulder and potential instability of the glenohumeral joint.
From the Research
Cervical Nerves Innervating the Subscapularis Muscle
The subscapularis muscle is innervated by the upper subscapular nerve and the lower subscapular nerve, which are branches of the brachial plexus. The brachial plexus is formed by the ventral rami of C5 to T1 spinal nerves 2.
Spinal Root Origins of the Subscapular Nerves
Studies have shown that the upper subscapular nerve tends to innervate the upper and middle portions of the subscapularis muscle, while the lower subscapular nerve tends to innervate the lower portion of the muscle 2. The spinal root origins of the lower subscapular nerve have been found to be composed of C5, C6, and C7 roots in 76.9% of cases, and C6 and C7 roots in 23.1% of cases 3.
Key Points
- The subscapularis muscle is innervated by the upper and lower subscapular nerves, which are branches of the brachial plexus 2.
- The upper subscapular nerve originates from the posterior cord in 97% of cases, and the lower subscapular nerve originates from the posterior cord in 79% of cases 4.
- The spinal root origins of the lower subscapular nerve are composed of C5, C6, and C7 roots in 76.9% of cases, and C6 and C7 roots in 23.1% of cases 3.
- The subscapular nerves play a crucial role in the innervation of the subscapularis muscle, and injury to these nerves can result in significant functional impairment 5, 6.