A 32-year-old male carpenter from Delhi presents with inability to oppose his thumb to other fingers and loss of sensation over the lateral palm and radial 3.5 digits. He reports a history of a deep laceration over the volar aspect of the wrist sustained 2 weeks ago during a work accident. On examination, he has weakness of thumb opposition and abduction, and sensory loss in the distribution described. Which nerve is injured and at what anatomical level?

Explanation

## Clinical Presentation Analysis **Key Point:** The combination of loss of thumb opposition (recurrent branch of median nerve) and sensory loss over the lateral palm and radial 3.5 digits (median nerve sensory distribution) indicates a **distal median nerve injury at or below the wrist**. ## Anatomical Basis ### Median Nerve Course at the Wrist The median nerve enters the carpal tunnel and gives off: 1. **Recurrent (motor) branch** — innervates thenar muscles (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis) 2. **Digital sensory branches** — supply lateral 3.5 fingers (thumb, index, middle, lateral half of ring finger) ### Motor Deficit - **Thumb opposition loss** = damage to recurrent branch (motor component) - Recurrent branch arises just distal to the flexor retinaculum - This is the classic **"ape hand" deformity** when combined with sensory loss ### Sensory Deficit - Lateral palm and radial 3.5 digits = classic median nerve sensory territory - Loss indicates injury distal to the point where sensory branches diverge **Clinical Pearl:** A wrist laceration affecting both motor (thenar) and sensory components of the median nerve must be at or distal to the carpal tunnel exit — this is a **distal median nerve lesion**. ## Why This Level? | Feature | Distal (Wrist) | Proximal (Elbow) | |---------|---|---| | Thumb opposition | Lost | Lost | | Forearm pronation | Normal | Weak | | Wrist/finger flexion | Weak | Weak | | Sensory loss | Lateral palm + 3.5 digits | Same | | **Mechanism** | **Laceration at wrist** | Crush/stretch injury | The history of a **volar wrist laceration** directly correlates with distal median nerve injury at the wrist level. **High-Yield:** Distal median nerve lesions spare forearm pronation (pronator teres is innervated proximal to the wrist) but lose thumb opposition — a key distinguishing feature.