Ulnar nerve entrapment

Ulnar nerve entrapment occurs when the ulnar nerve is compressed, typically at the elbow or the wrist. Compression at the elbow is called cubital tunnel syndrome; compression at the wrist it is referred to as Guyon's canal syndrome or ulnar tunnel syndrome. The compression causes paresthesias, numbness, and/or pain in the ulnar nerve distribution. Depending on the site of compression, the patient may experience weakness in certain hand muscles. Ulnar entrapment neuropathy may be suspected based on clinical symptoms and signs, but it must be confirmed by electromyography (EMG). Conservative treatment involves NSAIDs, behavior modification, and bracing. Severe, persistent, or worsening symptoms require surgical decompression.

Course of the ulnar nerve

• The ulnar nerve arises from the medial cord of the brachial plexus, which, in turn, arises from the nerve roots C8–T1.
• From the brachial plexus, the ulnar nerve courses through the medial bicipital sulcus and descends down the medial aspect of the arm medial to the brachial artery to the elbow.
• Passes the medial epicondylar groove at the elbow
• Enters the palm through the Guyon canal
• For more detailed information on motor and sensory innervation, see "Neurovasculature of the upper limbs."

Ulnar neuropathy at the elbow and wrist ^[1][2]

The ulnar nerve is most commonly compressed at or near the cubital tunnel of the elbow and Guyon canal of the wrist.

Motor symptoms

• Entrapment at the elbow
  • Less common than sensory complaints and range from mild to severe weakness
  • Muscle atrophy and weakness
    • Loss of dexterity
    • Decreased grip strength
    • Difficulty lifting
• Entrapment at the wrist: weakness and atrophy of the intrinsic hand muscles innervated by the ulnar nerve

Sensory symptoms

• Entrapment at the elbow
  • Paresthesia or sensory loss of palmar and dorsal aspects of the medial side of the hand, little finger, and ulnar side of the ring finger
  • Referred pain in the forearm
• Entrapment at the wrist
  • Variable paresthesia or sensory loss of the palmar and dorsal aspects of the medial side of the hand, little finger, and ulnar side of the ring finger
  • Compression of the ulnar nerve at the wrist is divided into three zones and exam findings often correlate with the site of injury.
    • Zone I: lesions proximal to the bifurcation of the ulnar nerve
      • Motor and sensory symptoms (i.e., sensory loss in the palmar surface of the little finger and medial aspect of the ring finger) possible
      • Sensory features similar to those caused by proximal lesions at the elbow
    • Zone II: lesions at the deep motor branch cause motor symptoms only
    • Zone III: lesions at the distal sensory branch cause sensory symptoms only

Physical examination

• Ulnar claw
  • Palsy of the 3^rd and 4^th lumbricals with preserved function of the extrinsic flexors
  • Present at rest, increases when the patient is asked to extend the fingers
  • Mainly seen in distal ulnar nerve injuries
• Froment sign
  • Flexion of the thumb at the interphalangeal joint elicited when tightly pressing together the tips of the index finger and thumb, or when tightly adducting the thumb against the 2nd metacarpal (e.g., pinching a piece of paper using the thumb)
  • Due to weakness of the adductor pollicis muscle and the unopposed action of flexor pollicis longus
• Wartenberg sign
  • Persistent abduction of the little finger
  • Due to weakness of the third palmar interosseous muscle
• Jeanne sign
  • Hyperextension of the MCP joint of the thumb with key pinch movement
  • Due to loss of function of the adductor pollicis muscle and predominance of the extensor pollicis longus and the abductor pollicis brevis
• Tinel sign: tapping on the medial epicondyle of the humerus elicits marked paresthesias in the ulnar portion of the hand

Ulnar claw deformity is mainly seen in distal ulnar nerve injuries, while difficulty making a fist occurs in proximal ulnar nerve injuries.

Proximal and distal lesions of the ulnar nerve lead to claw hand deformity.

• Electrodiagnostic studies (nerve conduction studies and EMG): identify the level of nerve compression
• Ultrasound and MRI: confirm EMG findings and identify the cause of compression

• Conservative therapy ^[2]
  • Modify behavior (e.g., avoid prolonged resting on elbow, repeated flexion of elbow)
  • Analgesia (e.g., NSAIDs)
  • Bracing at night
• Surgical decompression: if clinical features are severe, persistent (i.e., lasting more than 6 to 12 weeks), or progressively worsen despite conservative therapy