Learning Objectives
By the end of this section, the learner should be able to:
- Describe the location and function of the ulnar (cubital) tunnel
- Identify the borders, roof, and floor of the ulnar tunnel
- State the contents of the ulnar tunnel and their anatomical course
- Explain the pathophysiology and clinical features of cubital tunnel syndrome
Overview
The ulnar tunnel, commonly referred to as the cubital tunnel, is a fibro-osseous passage located on the posteromedial aspect of the elbow.
Its primary function is to transmit the ulnar nerve from the arm into the forearm, making it a key anatomical site for ulnar nerve compression.
Borders, Roof, and Floor
The ulnar tunnel is oval in shape and consists of medial and lateral walls, a floor, and a roof:
Walls
- Medial wall: medial epicondyle of the humerus
- Lateral wall: olecranon of the ulna
Floor
- Elbow joint capsule
- Medial (ulnar) collateral ligament of the elbow
Roof
- A fibrous band spanning between the medial epicondyle and the olecranon
This roof is formed by the cubital tunnel retinaculum, also known as the arcuate ligament of Osborne. It is a fascial band that extends between the humeral and ulnar heads of the flexor carpi ulnaris, completing the tunnel.
Contents
The ulnar tunnel transmits a single but clinically important structure: The ulnar nerve
After passing through the cubital tunnel, the ulnar nerve:
- Enters the forearm by passing between the two heads of the flexor carpi ulnaris
- Continues distally to supply the medial forearm, hand, and intrinsic hand muscles
Clinical Relevance: Cubital Tunnel Syndrome
Cubital tunnel syndrome results from compression of the ulnar nerve within the ulnar (cubital) tunnel. It is the second most common peripheral nerve entrapment in the upper limb, after carpal tunnel syndrome.
Sensory symptoms
- Numbness or tingling in the medial one and a half digits (little finger and medial half of the ring finger)
- Sensory loss over the medial palm
Motor symptoms (advanced cases)
Weakness and wasting of intrinsic hand muscles, including:
-
- Interossei
- Lumbricals (medial two)
- Hypothenar muscles
- Adductor pollicis
This may result in reduced grip strength and impaired finger abduction/adduction.
Effect of elbow position
- During elbow flexion, the cubital tunnel changes from an oval to an elliptical shape
- Tunnel volume decreases, and intratunnel pressure increases
- This explains why symptoms are often worsened by prolonged elbow flexion, such as during sleep or phone use.
