A 35-year-old male labourer presents with weakness of finger flexion and loss of sensation over the medial 1.5 fingers. On examination, claw hand deformity is noted. Which is the most common site of ulnar nerve compression in this patient?

Explanation

## Most Common Site of Ulnar Nerve Compression **Key Point:** The cubital tunnel at the elbow is responsible for approximately 50–60% of all ulnar nerve compression injuries, making it the most common site of entrapment in the upper limb. ### Anatomical Basis The cubital tunnel is formed by: - Medial epicondyle of the humerus (laterally) - Olecranon process (posteriorly) - Medial collateral ligament and flexor carpi ulnaris fascia (roof) The nerve is vulnerable here due to: - Superficial course around the medial epicondyle - Compression during elbow flexion - Repeated trauma from occupational activities - Prolonged pressure (e.g., leaning on elbows) ### Clinical Presentation in This Case The patient's symptoms (weakness of finger flexion, sensory loss in medial 1.5 fingers, and claw hand) are consistent with a **complete ulnar nerve lesion**, which commonly occurs at the cubital tunnel. **Mnemonic:** **CLAW** = **C**ubital tunnel is **L**ikely **A**ffected **W**hen hand deformity occurs ### Comparison of Ulnar Nerve Compression Sites | Site | Frequency | Clinical Features | Mechanism | | --- | --- | --- | --- | | **Cubital tunnel (elbow)** | 50–60% (most common) | Weakness of intrinsic muscles, sensory loss in ulnar distribution, claw hand | Compression during flexion, occupational trauma | | Guyon's canal (wrist) | 10–15% | Weakness of hypothenar muscles + adductor pollicis; **sparing of sensation** (superficial branch unaffected) | Ganglion, trauma, repetitive compression | | Arcade of Struthers | <5% | Rare; similar to cubital tunnel but proximal | Anatomical variant; muscular hypertrophy | | Deep flexor tunnel (forearm) | Rare | Weakness of flexor digitorum profundus to digits 4–5 | Occupational trauma, ganglion | **High-Yield:** Cubital tunnel syndrome is the second most common entrapment neuropathy overall (after carpal tunnel), and the most common in the upper limb after the wrist. **Clinical Pearl:** The "funny bone" sensation when striking the medial epicondyle reflects the superficial course of the ulnar nerve at the cubital tunnel—this anatomical vulnerability explains the high frequency of compression at this site.