M01.03.006 The Ulnar Tunnel

The ulnar (cubital) tunnel is a fibro-osseous passage located on the posteromedial aspect of the elbow. It transmits the ulnar nerve from the arm into the forearm. This article explores its borders, contents, and clinical relevance.

Anatomy of the Ulnar Tunnel

Borders

The ulnar tunnel is an oval-shaped space with distinct boundaries:

• Roof Description: The cubital tunnel retinaculum is a fascia band connecting the ulnar and humeral heads of the flexor carpi ulnaris.

Contents

• Ulnar nerve: The major peripheral nerve passing through the tunnel.
  • Pathway: After exiting the tunnel, the ulnar nerve traverses between the two heads of the flexor carpi ulnaris and continues into the forearm and hand.

Clinical Relevance

Cubital Tunnel Syndrome

This condition arises from the compression of the ulnar nerve within the ulnar tunnel. It is the second most common peripheral neuropathy in the upper limb after carpal tunnel syndrome.

Symptoms

• Sensory Changes:
  • Altered sensation in the medial one and a half fingers and the corresponding palm area (ulnar nerve distribution).
• Motor Deficits:
  • Weakness and wasting of intrinsic hand muscles, including:
    • Lumbricals
    • Interossei
    • Hypothenar eminence
    • Adductor pollicis

Exacerbation of Symptoms

• During elbow flexion, the shape of the tunnel changes from oval to elliptical, increasing pressure on the nerve and worsening symptoms.

Key Points to Remember

1. Location: Posteromedial aspect of the elbow.
2. Function: Transmits the ulnar nerve from the arm to the forearm.
3. Borders: Defined by the medial epicondyle, olecranon, elbow joint capsule, and cubital tunnel retinaculum.
4. Clinical Significance:
   • Compression can lead to sensory and motor deficits.
   • Elbow flexion exacerbates symptoms due to increased tunnel pressure.

Bibliography

• Authoritative sources on the ulnar tunnel and peripheral neuropathies.