What nerve is responsible for causing pain in the right upper arm?

Nerves Responsible for Right Upper Arm Pain

Pain in the right upper arm is most commonly caused by the brachial plexus, particularly its terminal branches including the axillary, musculocutaneous, and radial nerves. 1

Brachial Plexus Anatomy and Pain Distribution

The brachial plexus is formed from the C5 to T1 ventral rami and provides the primary innervation to the upper extremity. Its anatomical course is as follows:

• Originates from C5-T1 nerve roots (occasionally with contributions from C4 and/or T2)
• Passes between the anterior and middle scalene muscles with the subclavian artery
• Forms trunks, divisions, and cords before terminating in peripheral nerves
• Terminal branches continue through the axilla into the arm 1

Key Terminal Nerves Causing Upper Arm Pain

1. Axillary Nerve:

   • Courses through the quadrilateral space
   • Lies in intimate contact with the inferior shoulder capsule
   • Innervates the deltoid muscle and provides sensation to the lateral shoulder
   • Injury commonly occurs just proximal to the quadrilateral space 2, 3

2. Musculocutaneous Nerve:

   • Enters and travels through the coracobrachialis muscle
   • Changes shape from oval to flat-oval to triangular during its course
   • Provides motor innervation to the biceps and brachialis muscles
   • Provides sensory innervation to the lateral forearm 4

3. Radial Nerve:

   • Travels in the spiral groove of the humerus
   • Susceptible to compression at multiple points in the upper arm
   • Innervates the triceps and extensor muscles of the forearm
   • Provides sensation to the posterior arm and dorsal forearm 5

Clinical Presentation of Upper Arm Nerve Pain

Plexopathy or peripheral nerve injury may manifest as:

• Neuropathic pain with burning or electric sensation
• Dysesthesia in specific nerve distributions
• Weakness in muscles innervated by affected nerves
• Sensory loss in specific dermatomes
• Flaccid loss of tendon reflexes 1

Diagnostic Approach

1. Clinical Examination:

   • Manual muscle testing to identify specific weakness patterns
   • Pain on compression and/or positive Tinel sign
   • Assessment for positive scratch collapse test at compression points 5

2. Imaging Studies:

   • MRI of the brachial plexus is the mainstay of plexus imaging (rated 9/9 for appropriateness) 1
   • Should include orthogonal views through the oblique planes of the plexus
   • T1-weighted, T2-weighted, fat-saturated T2-weighted sequences
   • May include fat-saturated T1-weighted postcontrast sequences 1

3. Electrodiagnostic Studies:

   • Confirm clinical diagnosis of plexopathy
   • Should be obtained within 4 weeks after injury
   • Follow-up evaluation at 12 weeks 3

Positional Considerations

The position of the arm can significantly affect nerve location and tension:

• Abduction of the shoulder reduces the distance between the musculocutaneous nerve and axillary artery 6
• Limiting arm abduction to 90° in supine patients may reduce risk of brachial plexus neuropathy 1
• The prone position may allow patients to tolerate greater arm abduction 1

Prevention and Management

Protective Strategies

• Padded armboards may decrease risk of upper extremity neuropathy
• Chest rolls in laterally positioned patients help decrease brachial plexus neuropathy risk
• Padding at the elbow reduces risk of ulnar neuropathy
• Avoid prolonged pressure on the radial nerve in the spiral groove of the humerus 1

Treatment Options

• Most patients with axillary nerve injury recover with non-operative treatment
• If no clinical or electromyographic improvement is noted after 12 weeks, surgery may be considered
• Surgical options include neurolysis, nerve grafting, and neurotization
• Best results occur when surgery is performed within 3-6 months of injury 3

Common Pitfalls and Caveats

1. Diagnostic Challenges:

   • Low-level nerve compression may not be revealed in nerve conduction or MRI studies
   • Pain may be mistaken for musculoskeletal issues rather than nerve compression

2. Anatomical Variations:

   • Variations in nerve course and position (especially the musculocutaneous nerve) can make localization difficult 4
   • In some individuals, the musculocutaneous nerve may not be visualized within the coracobrachialis muscle

3. Differential Diagnosis:

   • Distinguish between plexopathy and radiculopathy (pain in a dermatomal distribution)
   • Consider atraumatic causes such as brachial neuritis and quadrilateral space syndrome 3

Early recognition and appropriate management of nerve compression or injury is essential to prevent chronic pain and functional impairment in the upper extremity.