Understanding Ulnar Nerve Facts

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

1. Causes of Ulnar Nerve Compression

• The most common cause:

  • Compression between the two heads of the flexor carpi ulnaris.

• Other causes include:

  • Anconeus epitrochlearis muscle.

  • Arcade of Struthers.

• Differentiate between:

  • Arcade of Struthers – may compress the ulnar nerve.

  • Ligament of Struthers – associated with compression of the median nerve (arises from a supracondylar spur).

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2. Origin of the Ulnar Nerve

• Root origin: C8–T1.

• Same root levels associated with:

  • Horner syndrome.

• Presence of Horner syndrome suggests a poor prognosis in brachial plexus injury.

• When asked which roots are involved in ulnar nerve function ? C8–T1.

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3. First Dorsal Interosseous Muscle

• Supplied by the ulnar nerve.

• Wasting indicates:

  • Ulnar nerve lesion.

  • Poor prognosis.

• Must differentiate from:

  • Thenar muscle wasting (median nerve involvement).

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4. Martin–Gruber Anastomosis

• An anatomic anomaly between:

  • Median nerve

  • Ulnar nerve

• Can confuse:

  • Clinical findings

  • EMG interpretation

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5. Effect of Elbow Flexion

• Elbow flexion decreases cubital tunnel space by approximately 40%.

• Excessive elbow flexion (e.g., prolonged cell phone use) may contribute to cubital tunnel syndrome.

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6. Dorsal Cutaneous Branch of the Ulnar Nerve

• Important for lesion localization.

• High ulnar nerve lesion (at elbow):

  • Loss of sensation over the dorsal medial hand.

  • Loss of sensation in medial one and a half fingers.

• Branches in the forearm:

  • Dorsal cutaneous branch

  • Palmar cutaneous branch

• Palmar cutaneous branch:

  • Supplies hypothenar area.

• At the hand:

  • Ulnar nerve divides into:

    • Deep branch (motor)

    • Superficial branch (sensory to one and a half fingers)

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7. Clawing of the Hand

Low Ulnar Nerve Lesion (Below Elbow)

• Causes clawing of the fourth and fifth fingers.

• Sensation over dorsal medial hand may be preserved.

High Ulnar Nerve Lesion (At Elbow)

• Loss of sensation over dorsal medial hand.

• May not produce significant clawing.

Mechanism of Clawing

• Ulnar nerve supplies:

  • Medial half of flexor digitorum profundus.

  • Intrinsic hand muscles (including lumbricals).

• In low ulnar palsy:

  • Intrinsics are paralyzed.

  • Flexor digitorum profundus to medial digits remains functional.

  • Results in clawing of the fourth and fifth fingers.

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8. Difference Between Clawing and Benedictine Sign

• Clawing (ulnar nerve):

  • Affects fourth and fifth digits.

• Benedictine sign:

  • Associated with anterior interosseous nerve injury.

  • Inability to flex the tip of the index finger.

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9. Wartenberg Sign

• Abduction of the fifth finger.

• Due to weakness of palmar interossei (loss of adduction).

• Caused by ulnar nerve dysfunction.

• Must differentiate from:

  • Wartenberg syndrome:

    • Entrapment of superficial radial nerve.

    • Occurs between brachioradialis and extensor carpi radialis longus.

    • May be irritated by tight handcuffs, watches, or bracelets.

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10. Froment Sign

• Tests adductor pollicis (ulnar nerve).

• When attempting to pinch paper:

  • Loss of thumb adduction.

  • Patient flexes thumb to compensate.

• Positive Froment sign indicates ulnar nerve dysfunction.

Important Distinction

• Median nerve function:

  • Ability to form the “OK” sign.

• Ulnar nerve dysfunction:

  • Abnormal pinch due to loss of adductor pollicis.

• Do not confuse:

  • Median nerve OK sign

  • Ulnar nerve weakness during pinch

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11. Tinel Sign at the Elbow

• Tapping over the medial elbow reproduces ulnar nerve symptoms.

• Useful in diagnosing cubital tunnel syndrome.

• If combined with medial epicondylitis:

  • Surgical outcomes may be less predictable.

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12. Differential Diagnosis

• Double crush syndrome.

• Cervical disc herniation with radicular compression.

• Thoracic outlet syndrome.

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13. Sensory Testing for Ulnar Nerve

• Decreased sensation in:

  • Fourth and fifth fingers.

• Useful bedside test, especially in:

  • Young patients

  • Post-anesthesia patients

• Sensory testing is easier than testing motor function in these situations.

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14. Ulnar Nerve Injury in Supracondylar Fracture (Children)

• Extension-type supracondylar fracture:

  • Typically associated with anterior interosseous nerve injury.

• Flexion-type supracondylar fracture:

  • Associated with ulnar nerve injury.

• May require open reduction in complex cases.