Although the fourth and fifth digits are held in the clawed position when the nerve is injured at the wrist, a high lesion paralyses the long flexors to these two fingers and results in the loss of this sign.
- The ulnar nerve is formed from the medial cord of the brachial plexus
- Passes behind the medial epicondyle where it is vulnerable to compression
- In the distal forearm it lies with the ulnar artery.
- Unlike the median nerve it passes into the hand above the flexor retinaculum and supplies
- Hypothenar muscles, Flexor carpi ulnaris
- Medial half of flexor digitorum profundus
- Interossei, 3rd and 4th lumbrical
- Rarely (2%) the ulnar nerve does supply all the muscles of the hand.
- Dorsal little and half of ring finger
- Palmar little and half of ring finger
- Vulnerable to pressure at ulnar groove at the medial elbow
- Compression distal to elbow
- Compression as it enters the hand through Guyon's canal
- Medical causes e.g. diabetes etc
- Numbness and pain over ulnar 1.5 digits on palmar/dorsal hand as it supplies sensation to the skin of the fifth and the ulnar side of the fourth finger, front and back and absence of sweating in the affected area
- Weakness with spreading fingers
- Weakness of flexion of ring/little finger
- No wasting thenar eminence as supplied by the median nerve
- Wasting of small muscles
- Clawed hand appearance "Benediction sign"
- Check elbow for trauma, arthritis, scars
- EMG/NCS - slowed conduction
- Carpal tunnel syndrome
- C8 radiculopathy also affects abductor pollicis brevis- EMG should help.
- Brachial plexus lesion - median nerve muscles also affected
- Fracture, arthritis, compression at elbow
- Wrist lesions - ganglion, fracture, tumour
- Mononeuritis multiplex
- Wrists splints unhelpful
- Protect ulnar nerve compression
- Surgical transposition of ulnar nerve and decompression