Which muscles in the neck and spine can cause a pinched nerve in the arm?

Muscles in the Neck and Spine That Can Cause Pinched Nerves in the Arm

The anterior scalene, middle scalene, and pectoralis minor muscles are the primary muscles that can cause nerve compression leading to pinched nerves in the arm, particularly through thoracic outlet syndrome mechanisms. 1

Anatomical Considerations

Primary Muscles Causing Compression

1. Scalene Muscles

   • Anterior scalene muscle: Forms the posterior border of the costoclavicular triangle and can compress the brachial plexus and subclavian artery 1
   • Middle scalene muscle: Creates the interscalene triangle with the anterior scalene, where trunks of the brachial plexus pass through 1

2. Pectoralis Minor Muscle

   • Defines the pectoralis minor space (between the muscle and chest wall)
   • Compression here affects neurovascular structures similar to costoclavicular space compression 1

3. Subclavius Muscle

   • Can hypertrophy and further narrow the costoclavicular space 1

Anatomical Spaces of Compression

1. Costoclavicular Triangle

   • Borders: Clavicle (superior), anterior scalene muscle (posterior), first rib (inferior)
   • Contains: Brachial plexus, subclavian artery, and subclavian vein
   • Compression here typically causes venous symptoms (venous TOS) 1

2. Interscalene Triangle

   • Borders: Anterior scalene, middle scalene, and first rib
   • Contains: Trunks of brachial plexus and subclavian artery
   • Compression here causes neurological (nTOS) or arterial (aTOS) symptoms 1

3. Pectoralis Minor Space

   • Extension of the thoracic outlet
   • Can cause varying degrees of compression similar to costoclavicular space 1

Mechanisms of Nerve Compression

Direct Compression Mechanisms

1. Muscle Hypertrophy

   • Enlarged muscles (especially scalenes and pectoralis minor) directly compress nerves 1
   • Common in athletes with repetitive upper extremity movements (swimmers, throwers)

2. Postural Factors

   • Extreme shoulder abduction naturally narrows the costoclavicular space 1
   • Repetitive stress leads to muscle thickening and fibrosis

3. Anatomical Variants

   • Cervical rib can cause narrowing of the scalene triangle 1
   • Anomalous first rib or post-traumatic changes from prior clavicular/rib fractures

Cervical Radiculopathy Considerations

Cervical radiculopathy presents with similar symptoms but involves nerve root compression at the spine level:

• Most commonly stems from degenerative disease in the cervical spine 1
• Can be caused by facet or uncovertebral joint hypertrophy compressing nerve roots 1
• Disc bulging or herniation can also compress nerve roots causing arm symptoms 1

Clinical Presentation

Symptoms Based on Compression Site

1. Neurological Thoracic Outlet Syndrome (nTOS)

   • Chronic arm/hand paresthesia, numbness, or weakness
   • Caused by compression in the interscalene triangle 1

2. Venous TOS (vTOS)

   • Venous symptoms predominate
   • Typically from costoclavicular space compression 1

3. Arterial TOS (aTOS)

   • Arterial symptoms with risk of distal embolization
   • Can include aneurysm formation 1

4. Cervical Radiculopathy

   • Pain in neck with radiation to arm in dermatomal pattern
   • Often accompanied by sensory or motor deficits in nerve root distribution 2

Diagnostic Approach

Physical Examination

• Painful neck movements and muscle spasm are common findings 3
• Diminished deep tendon reflexes (especially triceps) suggest radiculopathy 3
• Spurling test, shoulder abduction test, and upper limb tension test can confirm radiculopathy 3

Imaging

• MRI is the preferred imaging modality for diagnosing radiculopathy 2
• CT provides good definition of bony elements for assessing neuroforaminal stenosis 1
• For thoracic outlet syndrome, specific protocols with neutral and stressed positions (arms abducted) may be required 1

Treatment Considerations

Conservative Management

• Most cases resolve regardless of treatment type 3
• Physical therapy involving strengthening, stretching, and potentially traction 3
• Neural tissue management techniques can provide immediate benefits for nerve-related neck and arm pain 4

Medication Options

• NSAIDs as first-line medication for pain 2
• Muscle relaxants may help with muscle spasm 3

Interventional Options

• Targeted epidural steroid injections under fluoroscopic guidance for persistent symptoms 2
• Surgical decompression for progressive neurological deficit or significant compression 2

Common Pitfalls

1. Misdiagnosis

   • Cervical spine and shoulder problems frequently have similar presentations 5
   • Incomplete neurological examination can lead to misdiagnosis 2

2. Overlooking Combined Pathology

   • Combined neck and arm pain is more disabling than either symptom alone 6
   • Multiple compression sites may coexist

3. Delayed Treatment

   • Chronic symptoms can negatively impact mental health 6
   • Earlier intervention (within 2 weeks) for severe radicular pain may improve outcomes 2

4. Neglecting Psychosocial Factors

   • Psychosocial factors are stronger predictors of outcomes than physical examination findings 2

Understanding the complex interplay between muscular compression and nerve pathology is essential for proper diagnosis and treatment of pinched nerves affecting the arm.