Anatomy Msk · Year 1 · from Anatomy Msk
Case 3: Ulnar Nerve Entrapment at the Cubital Tunnel
Clinical Image
Source: Wikimedia Commons - Ulnar Nerve - CC BY-SA 4.0
Case Presentation
A 48-year-old accountant presents with 4 months of progressive numbness and tingling in his left small finger and the ulnar half of his ring finger. Symptoms are worse after prolonged elbow flexion, such as when talking on the phone or sleeping. He has noticed weakness when trying to spread his fingers apart and clumsiness with fine motor tasks like buttoning his shirt. Physical examination reveals decreased sensation in the ulnar 1.5 digits, both dorsally and volarly. There is visible atrophy of the first dorsal interosseous muscle. Weakness is noted with finger abduction (interossei), finger adduction, and thumb adduction (adductor pollicis). Froment's sign is positive - he flexes his thumb IP joint when attempting to grip paper between thumb and index finger (compensating with FPL due to adductor weakness). Tinel sign is positive at the cubital tunnel (posterior to the medial epicondyle). There is subluxation of the ulnar nerve over the medial epicondyle with elbow flexion. Nerve conduction studies confirm ulnar neuropathy at the elbow with slowing of conduction velocity across the cubital tunnel. He undergoes cubital tunnel release with anterior submuscular transposition.
Key Learning Points
- The ulnar nerve passes posterior to the medial epicondyle through the cubital tunnel (formed by medial epicondyle and olecranon)
- The cubital tunnel is the most common site of ulnar nerve compression (second most common compression neuropathy after CTS)
- Ulnar nerve supplies all interossei, medial two lumbricals, hypothenar muscles, and adductor pollicis
- Sensory distribution: ulnar 1.5 digits (small finger + ulnar ring finger), both dorsal and volar surfaces
- Froment's sign indicates adductor pollicis weakness; Wartenberg sign (small finger abduction) indicates interosseous weakness