A 28-year-old male carpenter presents with weakness of thumb opposition and abduction, along with sensory loss over the lateral three and a half fingers. Which is the most common site of median nerve compression in this patient?

Explanation

## Most Common Site of Median Nerve Compression **Key Point:** Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy of the median nerve, accounting for >50% of all nerve compression syndromes. ### Clinical Presentation in This Case The patient's symptoms—weakness of thumb opposition and abduction (thenar muscles) with sensory loss in the lateral 3.5 fingers—are classic for median nerve compression at the wrist. The recurrent motor branch (branch to thenar muscles) arises distal to the carpal tunnel, making thenar weakness a hallmark of CTS. ### Anatomical Basis | Site | Frequency | Key Features | |------|-----------|-------------| | **Carpal tunnel (wrist)** | ~50–60% of median nerve lesions | Affects recurrent motor branch + sensory branches; most common | | Pronator teres (forearm) | ~10–15% | Anterior interosseous nerve (AIN) may also be involved | | Ligament of Struthers | <5% | Rare; above elbow; may compress median nerve and brachial artery | | AIN at elbow | ~5–10% | Isolated motor loss; no sensory involvement | **High-Yield:** CTS is 3–4 times more common in women and increases with age, repetitive wrist use, and metabolic conditions (diabetes, hypothyroidism, pregnancy). ### Why Carpal Tunnel is Most Common 1. **Anatomical narrowing:** The carpal tunnel is a fixed osseofibrotic space; any swelling (tenosynovitis, ganglion, thickened ligament) causes compression. 2. **Occupational exposure:** Repetitive wrist flexion/extension increases intraneural pressure. 3. **Systemic associations:** Pregnancy, rheumatoid arthritis, and hypothyroidism predispose to CTS. **Clinical Pearl:** Tinel's sign (percussion over median nerve at wrist) and Phalen's test (sustained wrist flexion) are bedside confirmatory tests; EMG/NCS is the gold standard for diagnosis.