FMGE 2013 — Anatomy

Question 1: Partial claw hand is caused by lesion involving the:

• A. Anterior interosseous nerve
• B. Radial nerve
• C. Median nerve
• D. Ulnar nerve (Correct Answer)

Explanation: ***Ulnar nerve*** - A lesion of the **ulnar nerve** causes a **partial claw hand** (also called "ulnar claw") because the **medial two lumbricals** (which flex the MCP joints and extend the IP joints of the 4th and 5th digits) and the **interossei** are paralyzed [1]. - This leads to hyperextension at the **metacarpophalangeal (MCP) joints** and flexion at the **interphalangeal (IP) joints** of the **4th and 5th fingers only** (hence "partial") [1]. - The lateral two fingers (index and middle) are spared because their lumbricals are supplied by the median nerve [1]. *Anterior interosseous nerve* - Injury to the **anterior interosseous nerve** primarily affects the **flexor pollicis longus**, **flexor digitorum profundus** (index and middle fingers), and **pronator quadratus**. - This results in the inability to make an "OK" sign (pinch sign) and does not typically cause a claw hand deformity. *Radial nerve* - A **radial nerve** lesion leads to **wrist drop** and the inability to extend the wrist and fingers. - This deformity is distinct from a claw hand, which involves hyperextension at the MCP joints and flexion at the IP joints. *Median nerve* - A **median nerve** lesion results in a "hand of benediction" or "ape hand" deformity, affecting the **thenar muscles** and the **lateral two lumbricals** [1]. - This involves paralysis of the thumb's opposition and the inability to flex the index and middle fingers, not the characteristic clawing of the 4th and 5th digits.