Paial claw hand is caused by lesion involving the: March 2010, March 2013 (a, b)
## **Core Concept**
The question pertains to the clinical presentation of "claw hand" or "ulnar claw hand," which is associated with nerve damage. Specifically, it involves the **ulnar nerve**, which controls muscle function and sensation in the hand.
## **Why the Correct Answer is Right**
The ulnar nerve innervates the **interossei** and **lumbricals 3 and 4** muscles, which are crucial for finger spreading and flexion at the MCP joints and extension at the IP joints. A lesion affecting the ulnar nerve leads to weakness of these muscles, causing the **intrinsic minus hand** or **ulnar claw hand** deformity. This deformity is characterized by hyperextension of the MCP joints and flexion of the IP joints of the 4th and 5th fingers, resembling a claw.
## **Why Each Wrong Option is Incorrect**
- **Option A:** The **median nerve** primarily controls the **thenar muscles** (thumb movements) and sensation to the palmar surface of the thumb, index, middle finger, and half of the ring finger. Damage to the median nerve leads to **ape hand deformity** or **simian hand**, not claw hand.
- **Option B:** The **radial nerve** primarily controls wrist and finger extension. Damage to the radial nerve results in **wrist drop**, not claw hand.
- **Option D:** The **musculocutaneous nerve** innervates the **biceps brachii**, **brachialis**, and **coracobrachialis** muscles. Its lesion leads to weakness in elbow flexion and forearm supination but not claw hand.
## **Clinical Pearl / High-Yield Fact**
A key clinical feature to remember is that an ulnar nerve lesion can cause a **claw hand** deformity, which affects the 4th and 5th fingers. A helpful clinical test is the **Froment's sign**, where a patient is asked to hold a piece of paper between their thumb and index finger; a positive sign (indicating ulnar nerve damage) is when the patient compensates by using their **adductor pollicis** (innervated by the ulnar nerve) to try to hold the paper.
## **Correct Answer:** C. Ulnar nerve.