Clinical Science Practice Part 2 (1)

Ulnar Nerve Injury: Abduction and Adduction

An ulnar nerve injury can lead to significant sensory and motor disturbances, particularly affecting the hand's ability to perform abduction and adduction movements of the fingers.

Key Points:

• Affected Muscles: The main muscles responsible for abduction (spreading fingers apart) and adduction (bringing fingers together) include the interossei muscles, which are innervated by the ulnar nerve.

• Testing Function: When assessing for ulnar nerve injury, the important muscular functions to test involve:

  • Abduction of the fingers: Moving fingers away from the midline (e.g., spreading fingers apart with resistance).

  • Adduction of the fingers: Moving fingers towards the midline (e.g., bringing fingers together against resistance).

• Clinical Effects: An injury can result in weakness in performing these movements, affecting hand function and grip strength substantially.

• Signs: The presence of Froment’s sign indicates weakness of the interossei muscles, which can manifest as compensatory effort using the flexor pollicis longus instead during testing, due to the inability to properly control the muscles supplied by the ulnar nerve.

• Claw Hand Deformity: One characteristic of severe ulnar nerve injury is the claw hand appearance, where hyperextension occurs at the metacarpophalangeal (MCP) joints and flexion at the interphalangeal (IP) joints primarily of the ring and little fingers, further demonstrating the consequences of impaired abduction and adduction.

Overall, an understanding of how ulnar nerve injuries affect finger abduction and adduction is essential for diagnosing, managing, and rehabilitating patients with such conditions.