What are the causes of a thickened ulnar nerve at the elbow?

Causes of Thickened Ulnar Nerve at Elbow

Ulnar nerve compression (cubital tunnel syndrome) is the primary cause of a thickened ulnar nerve at the elbow, which can lead to significant morbidity and decreased quality of life if left untreated. 1

Primary Causes of Ulnar Nerve Thickening

Mechanical Factors

• Repetitive elbow pressure or trauma 1
• Chronic compression at any of these five anatomical sites:
  • Arcade of Struthers (proximal)
  • Medial intermuscular septum
  • Medial epicondylar groove (most common site) 2
  • Cubital tunnel proper (between the two heads of flexor carpi ulnaris - second most common site) 2
  • Exit point from flexor carpi ulnaris (distal) 3
• Repetitive elbow flexion causing:
  • 55% decrease in cubital tunnel volume 4
  • Increased intraneural and extraneural pressures (up to 200 mmHg) 4
  • Nerve elongation of 4.7-8mm during elbow flexion 4

Positional Factors

• Prolonged elbow flexion 4
• Improper positioning during anesthesia/surgery 5
• Pressure in the ulnar groove from contact with hard surfaces 5

Pathological Findings

• T2-weighted MRI shows high signal intensity and nerve enlargement 5
• Ultrasound demonstrates increased cross-sectional area/nerve thickness 5
• Hourglass constriction of the nerve may be visible on ultrasound 5

Diagnostic Approach

Initial Imaging

• Radiography is the first-line imaging modality for elbow pain 5, 6
• Helps rule out other causes of medial elbow pain 6

Advanced Imaging

• MRI (particularly T2-weighted MR neurography) is the reference standard for imaging ulnar nerve entrapment 5

  • Findings include high signal intensity and nerve enlargement
  • Diffusion-tensor imaging increases diagnostic confidence
  • 3T MRI has fair-to-moderate agreement for localization of compression points

• Ultrasound is an excellent alternative for evaluation 5

  • Assessment of cross-sectional area/nerve thickness has high accuracy
  • Dynamic ultrasound can demonstrate nerve dislocation
  • Shear-wave elastography shows high specificity and sensitivity

• CT may be useful in specific cases 5

  • CT axial images in flexion and extension can demonstrate recurrent ulnar nerve dislocation due to snapping of the medial head of the triceps

Clinical Implications

Symptoms of Ulnar Nerve Thickening

• Earliest sign: Numbness and tingling of the ring and small fingers 1
• Progression to:
  • Paresthesia in ulnar nerve distribution
  • Clumsiness of the hand
  • Hand atrophy and weakness
  • Pain and point tenderness at the medial elbow 1

Risk Factors

• Repetitive elbow motion
• Prolonged elbow flexion
• Direct compression
• History of elbow trauma or injury 1

Age-Related Presentation

• Older patients: Tend to present with motor symptoms of chronic onset
• Younger patients: Tend to have more acute symptoms 1

Management Considerations

When ulnar nerve thickening is identified, treatment options include:

Conservative Management (First-Line)

• Activity modification and rest
• Elbow splints and braces
• Night-gliding exercises 1

Surgical Options (For Refractory Cases)

• Simple decompression in situ 7
• Subtotal medial epicondylectomy 3
• Anterior transposition (subcutaneous, intramuscular, or submuscular) 1

Pitfalls to Avoid

• Failure to recognize multiple sites of compression
• Overlooking systemic metabolic disorders that can mimic or exacerbate symptoms 2
• Delayed treatment leading to permanent muscle atrophy and functional impairment 1

MRI and ultrasound are the most valuable tools for confirming the diagnosis and determining the exact location and extent of nerve thickening, which is essential for proper treatment planning.