Is numbness of the fourth and fifth fingers due to ulnar nerve involvement?

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Ulnar Nerve and Numbness of the 4th and 5th Fingers

Yes, the ulnar nerve is responsible for causing numbness in the fourth (ring) and fifth (little) fingers, specifically affecting the medial half of the fourth finger and the entire fifth finger. 1, 2, 3, 4

Anatomical Distribution of Ulnar Nerve Sensory Innervation

The ulnar nerve provides sensation to:

  • The entire fifth (little) finger 3, 4
  • The medial (ulnar) half of the fourth (ring) finger 3, 4
  • The medial border of the hand 3

Important distinction: The medial forearm is NOT innervated by the ulnar nerve—it receives sensation from the medial antebrachial cutaneous nerve. 3 This is a common clinical pitfall, as a survey of 24 experienced spine surgeons found that only 63% correctly identified that severing the ulnar nerve results in numbness of the fourth and fifth fingers without affecting the forearm. 3

Clinical Presentation of Ulnar Neuropathy

When ulnar nerve compression or injury occurs (most commonly at the elbow in cubital tunnel syndrome), patients typically present with:

  • Paresthesia and numbness in the little finger and medial half of the fourth digit 4
  • Weakness of the small muscles of the hand innervated by the ulnar nerve 4
  • Positive Tinel's sign at the site of compression 4

Differentiating Ulnar Neuropathy from C8-T1 Radiculopathy

Critical clinical distinction: While both conditions can cause numbness in the fourth and fifth fingers, examining specific muscles helps differentiate them:

The ulnar nerve innervates all intrinsic hand muscles EXCEPT:

  • Abductor pollicis brevis 3
  • Flexor pollicis brevis 3
  • Opponens pollicis 3
  • Lateral two lumbricals 3

These four muscles are innervated by C8-T1 via the median nerve. 3 Testing these five muscles clinically differentiates cubital tunnel syndrome from C8-T1 radiculopathies. 3

Diagnostic Confirmation

Electrodiagnostic studies are essential to confirm the diagnosis, localize the compression site, differentiate demyelinating from axonal injury, and establish baseline severity. 1, 2 MRI without IV contrast is the reference standard for imaging, showing high signal intensity and nerve enlargement on T2-weighted neurography. 1, 2

References

1
Guideline

Treatment of Ulnar Nerve Impingement

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

2
Guideline

Diagnostic Approach and Management of Ulnar Nerve Entrapment

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

4
Research

Surgical treatment of ulnar neuropathy.

Surgical neurology, 1979

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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