Ulnar Nerve Palsy

Nerve supply

• Motor
  • Forearm
    • Flexor carpi ulnaris
    • Medial half of flexor digitorum profundus (distal interphalangeal joint)
  • Small muscles of the hand
    • Abductor digiti minimi
    • Opponens digiti minimi
    • Flexor digiti minimi
    • Medial two lumbricals
    • Interosseous muscles
    • Adductor pollicis
• Sensory
  • Palmar and dorsal aspects of medial 1½ fingers

Examination

• Inspection
  • Wasting of the hypothenar eminence
  • Ulnar claw, especially when opening hand
    • Results from unopposed extension of the MCPJ (paralysis of medial two lumbricals) and flexion of the DIPJ (medial half of FDP)
    • Ulnar paradox: lesions at the wrist result in a more deformed claw. More proximal lesions will paralyse the medial half of FDP, reducing the flexion deformity when the patient is asked to extend his fingers
  • Scars / deformities / fractures at elbow and wrist
• Power
  • Finger abduction
  • Finger adduction
  • Thumb adduction (best to test in extension)
    • Froment’s sign: ask the patient to hold a piece of paper between an extended thumb and the adjacent index finger. Pull the paper out of this pincer grip – the sign is positive if the patient flexes or abducts the thumb to main his grip on the paper.
  • Fourth and fifth finger FDP power (fix middle phalanx, ask patient to flex DIPJ)
    • If preserved, lesion is distal
  • Wrist flexion in the ulnar direction (FCU)
• Sensation
  • Numbness over ulnar 1½ digits
  • Numbness over the radial half of the 4^th finger implies a C8 lesion, not an ulnar lesion

Differential diagnosis

• C8 / T1 palsy
• Cervical syringomyelia

 Causes of ulnar nerve palsy

• Lesions at the elbow
  • Fracture
  • Arthritis / osteophytes
  • Compression during surgical procedure
  • Compression from prolonged leaning on a flexed elbow
  • Cubital tunnel syndrome
• Lesions at the wrist
  • Hook of hamate fracture
  • Lacerations
  • Repetitive strain injury (e.g. due to propulsion of a wheelchair)
  • Ganglia arising from within the wrist
• General mononeuritis
  • Leprosy
  • Vasculitis
  • Hereditary neuropathy
  • Acromegaly

Investigations

• Nerve conduction studies to confirm diagnosis
• Radiographs of wrist and elbow if underlying fracture suspected

Management

• Multidisciplinary approach
• Splinting, avoidance of exacerbating activities
• Consider surgical decompression