Suprascapular nerve

Medically Reviewed by Anatomy Team

The suprascapular nerve is a peripheral nerve that arises from the upper trunk of the brachial plexus, typically receiving contributions from the C5 and C6 spinal nerve roots. It primarily provides motor innervation to the supraspinatus and infraspinatus muscles and carries sensory fibers from the glenohumeral joint.

Location

The suprascapular nerve originates from the upper trunk of the brachial plexus in the neck and travels laterally and posteriorly. It passes beneath the trapezius muscle and through the suprascapular notch of the scapula, under the cover of the superior transverse scapular ligament. From there, it enters the supraspinous fossa to innervate the supraspinatus muscle. The nerve then continues around the lateral border of the scapular spine to reach the infraspinous fossa, where it innervates the infraspinatus muscle.

Anatomy

Origin

The suprascapular nerve arises from the upper trunk of the brachial plexus, which is formed by the union of the anterior rami of the C5 and C6 spinal nerves. It originates high in the posterior triangle of the neck, just after the merging of the roots to form the upper trunk.

Course

Cervical Region

  • After its origin from the upper trunk of the brachial plexus, the suprascapular nerve travels laterally and posteriorly across the lower part of the neck, deep to the omohyoid muscle and other neck muscles.
  • It runs beneath the trapezius muscle and remains deep as it approaches the shoulder area, directed toward the superior border of the scapula.

Passage Through Suprascapular Notch

  • As the nerve reaches the superior border of the scapula, it enters the suprascapular notch. This is a key anatomical landmark where the nerve passes beneath the superior transverse scapular ligament, which bridges the notch. The suprascapular artery, by contrast, runs above the ligament, while the nerve travels below.
  • After passing through the suprascapular notch, the nerve enters the supraspinous fossa of the scapula.

Supraspinous Fossa

  • Once in the supraspinous fossa, the suprascapular nerve supplies motor innervation to the supraspinatus muscle, which is located in this region. The nerve branches here to innervate the muscle fibers.
  • It continues its path along the base of the scapular spine, staying close to the bone and running deep to the supraspinatus muscle.

Infraspinous Fossa

  • After innervating the supraspinatus, the nerve travels laterally and inferiorly around the spine of the scapula to reach the infraspinous fossa.
  • In the infraspinous fossa, the nerve innervates the infraspinatus muscle, a major muscle involved in shoulder rotation.
  • The nerve also sends branches to the glenohumeral (shoulder) joint, contributing to its sensory innervation.

Branching

The suprascapular nerve branches into several smaller divisions as it reaches the muscles and structures it innervates:

  • Supraspinatus Branches: These branches supply the supraspinatus muscle, located in the supraspinous fossa.
  • Infraspinatus Branches: These branches travel deeper and longer to innervate the infraspinatus muscle in the infraspinous fossa.
  • Articular Branches: The nerve also sends articular branches to the glenohumeral joint, providing sensory input from the joint capsule.

Relations

  • Superior Transverse Scapular Ligament: The suprascapular nerve passes beneath the superior transverse scapular ligament, while the accompanying suprascapular artery passes above it. This relationship is clinically important as the nerve is susceptible to compression at this point, especially in cases of thickened ligaments or trauma.
  • Muscle Relations: The nerve runs deep to the trapezius and omohyoid muscles as it crosses the neck and approaches the scapula. It is closely related to the supraspinatus and infraspinatus muscles as it innervates them, traveling deep within the musculature of the scapula.
  • Artery Relations: The suprascapular artery follows a similar path as the nerve but passes above the superior transverse scapular ligament while the nerve passes below it.

Termination

The suprascapular nerve terminates after supplying motor innervation to the infraspinatus muscle in the infraspinous fossa. It does not continue beyond this point, although its sensory branches to the glenohumeral joint persist, providing sensory input from the shoulder capsule.

Anatomical Variations

  • In some individuals, the suprascapular nerve may show slight variations in its course or in its relation to the suprascapular notch and ligament. Rarely, the nerve may pass over the ligament instead of beneath it, which may predispose the nerve to injury in certain circumstances.

Function of the Suprascapular Nerve

The suprascapular nerve serves primarily a motor function, innervating two key muscles in the shoulder region: the supraspinatus and infraspinatus muscles. It also provides sensory input to the shoulder joint, specifically the glenohumeral joint. These functions are critical for shoulder stability and movement, particularly in rotation and abduction of the arm.

Motor Innervation of the Supraspinatus Muscle

The suprascapular nerve innervates the supraspinatus muscle, which is located in the supraspinous fossa of the scapula. The supraspinatus is one of the four muscles that make up the rotator cuff, a group of muscles crucial for shoulder movement and stability.

Function of the Supraspinatus Muscle

  • Abduction of the Arm
    • The primary function of the supraspinatus muscle, facilitated by the suprascapular nerve, is to initiate the first 15 degrees of arm abduction (raising the arm away from the body). Beyond 15 degrees, the deltoid muscle takes over, but the supraspinatus is essential for starting this movement.
  • Stabilization of the Shoulder Joint
    • The supraspinatus also plays a significant role in stabilizing the glenohumeral joint. By maintaining tension on the humeral head, the muscle prevents dislocation or excessive movement of the humerus from the shallow glenoid cavity during arm movements.

Motor Innervation of the Infraspinatus Muscle

The suprascapular nerve also innervates the infraspinatus muscle, located in the infraspinous fossa of the scapula. Like the supraspinatus, the infraspinatus is a key component of the rotator cuff.

Function of the Infraspinatus Muscle

  • Lateral (External) Rotation of the Arm
    • The infraspinatus muscle is one of the primary muscles responsible for lateral (external) rotation of the humerus. This movement involves rotating the arm outward, away from the body, and is crucial for actions such as throwing, swinging a bat, or reaching backward.
  • Stabilization of the Shoulder Joint
    • Similar to the supraspinatus, the infraspinatus plays a key role in stabilizing the shoulder joint by helping maintain the humeral head within the glenoid cavity, particularly during dynamic arm movements like overhead activities or lifting.

Sensory Innervation

In addition to its motor functions, the suprascapular nerve provides sensory fibers to the glenohumeral joint (shoulder joint).

Sensory Input from the Glenohumeral Joint

  • Proprioception: The suprascapular nerve helps relay information about the position and movement of the shoulder joint (proprioception) back to the central nervous system. This feedback is essential for coordinated arm and shoulder movements.
  • Pain and Temperature Sensation: While primarily motor, the suprascapular nerve carries some sensory fibers that provide pain and temperature sensation from the shoulder joint capsule. This sensory input can be critical in detecting and responding to joint injury or inflammation.

Role in Shoulder Movements

The suprascapular nerve plays a critical role in various shoulder movements through its innervation of the supraspinatus and infraspinatus muscles. These muscles work together with the rest of the rotator cuff to provide a full range of shoulder motion:

  • Arm Abduction
    • The suprascapular nerve allows the supraspinatus muscle to initiate abduction of the arm. Without proper function of this nerve, the initial phase of arm elevation would be compromised, making overhead activities difficult.
  • Arm Rotation
    • The infraspinatus muscle, innervated by the suprascapular nerve, is vital for external rotation of the arm, a movement required for activities like reaching behind the head or throwing. This rotation also complements other shoulder movements, enabling complex upper limb actions.
  • Shoulder Stability
    • Both the supraspinatus and infraspinatus contribute to the stabilization of the shoulder joint. The suprascapular nerve ensures that these muscles function properly to hold the head of the humerus securely in the shallow glenoid cavity, reducing the risk of shoulder dislocation or excessive movement during dynamic activities.

Synergistic Role with Other Muscles

The suprascapular nerve, through its control of the supraspinatus and infraspinatus muscles, works synergistically with the other muscles of the rotator cuff (subscapularis, teres minor, and deltoid) to provide smooth and coordinated shoulder movements. The nerve ensures proper timing and activation of the supraspinatus and infraspinatus, which are critical for maintaining shoulder function and preventing injury.

Clinical Significance

The suprascapular nerve is clinically important due to its role in the motor innervation of the supraspinatus and infraspinatus muscles, both key components of the rotator cuff. Injury or damage to this nerve can result in weakness or paralysis of these muscles, affecting shoulder function and leading to conditions like rotator cuff syndrome or shoulder instability.

Common Causes of Injury

  • Compression in the Suprascapular Notch: The suprascapular nerve is prone to compression as it passes under the superior transverse scapular ligament in the suprascapular notch. This can lead to suprascapular nerve entrapment, causing pain, weakness, and atrophy of the supraspinatus and infraspinatus muscles.
  • Trauma or Repetitive Strain: Direct trauma to the shoulder, repetitive overhead activities (such as in athletes), or conditions like a ganglion cyst can compress or damage the nerve.

Clinical Manifestations

  • Weakness in Shoulder Movements: Injury to the suprascapular nerve can lead to weakness in arm abduction (due to loss of supraspinatus function) and external rotation (due to loss of infraspinatus function), making tasks like lifting or throwing difficult.
  • Atrophy of the Shoulder Muscles: Over time, nerve damage may lead to visible atrophy of the supraspinatus and infraspinatus muscles, further compromising shoulder stability and movement.

Diagnosis and Treatment

  • Diagnosis: Nerve conduction studies, electromyography (EMG), and imaging (such as MRI) can help identify suprascapular nerve injury or compression.
  • Treatment: Management may involve physical therapy, corticosteroid injections, or in severe cases, surgical decompression of the nerve to relieve compression and restore function.

Also Read:

  1. Infraspinatus muscle
  2. Supraspinatus muscle
  3. Fossa
  4. Teres major muscle
  5. Teres minor muscle

In this Article:

  • Last updated on December 4, 2024