- Clinical science
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.
- Derived from nerve roots C8–T1
- Medial cord of the brachial plexus → ulnar nerve branch
- Sensory distribution: dorsal and palmar surface of the medial/ulnar one and a half fingers
- Third and fourth lumbricals: flex at MCP joint and extend at proximal interphalangeal (PIP) joint
- Adductor pollicis: adducts the thumb
- Abductor digiti minimi: abducts the little finger
- Flexor carpi ulnaris: helps flex the wrist
- Dorsal and palmar interossei: finger abduction and adduction respectively
- Cubital tunnel syndrome
- Guyon canal syndrome
Muscle weakness and atrophy
- Claw hand deformity: little and ring finger loss of extension at proximal interphalangeal joint and loss of flexion at metacarpal phalangeal joint
- Wartenberg sign: little finger in persistent abduction due to weak third palmar interosseous muscle
- Froment sign: The thumb flexes at the interphalangeal joint while pinching a piece of paper to compensate for a weak adductor pollicis muscle.
- Sensory loss
- Pain: Elbow lesions typically present with referred pain in the forearm.
Proximal as well as distal lesions lead to claw hand deformity!
- EMG: main confirmatory diagnostic test; it identifies the level of nerve compression.
- Ultrasound and MRI: used to support the EMG findings and to detect possible causes of compression (e.g., space-occupying lesions)
- Conservative therapy
- Surgical decompression if clinical features are severe, persistent (lasting more than 6–12 weeks), or progressively worsen despite conservative therapy.