cubital tunnel syndrome

**Anatomy:** The ulnar nerve (C8-T1, medial cord of the brachial plexus) passes posterior to the medial epicondyle through the cubital tunnel. The roof is the cubital tunnel retinaculum (Osborne's ligament), and the floor is the medial collateral ligament and elbow joint capsule. The tunnel then continues between the two heads of flexor carpi ulnaris (FCU). The "funny bone" is the ulnar nerve at this site.

**Pathophysiology:** Elbow flexion narrows the tunnel and stretches the nerve. Intraneural pressure rises and the nerve is also pulled over the epicondyle. Repetitive or prolonged flexion (for example, sleeping with the elbows bent or holding a phone) causes chronic compression and ischemia, which lead to demyelination and then axonal loss. Other causes and risk factors: - Direct pressure from leaning on the elbow - Prior elbow fracture or arthritis (cubitus valgus, tardy ulnar nerve palsy) - Ulnar nerve subluxation over the epicondyle - Anconeus epitrochlearis (an anomalous muscle) - Ganglia or osteophytes - Diabetes and other conditions that make nerves vulnerable

**Clinical features:** - Paresthesias and numbness of the little finger and the ulnar half of the ring finger. They are often worse at night or with elbow flexion. - Sensory loss over the dorsal ulnar hand, which suggests a lesion proximal to the wrist. The dorsal cutaneous branch arises about 5 cm proximal to the wrist, so it is spared in Guyon canal syndrome. - Medial elbow pain - Later findings: weak grip and pinch, clumsiness, and atrophy of the hypothenar muscles and first dorsal interosseous - Froment sign (thumb IP flexion by the flexor pollicis longus to compensate for a weak adductor pollicis) - Wartenberg sign (abducted little finger) - Crowe sign - Ulnar claw (hyperextension at the MCP joints and flexion at the IP joints of digits 4 and 5). It is more pronounced with distal (wrist) lesions because proximal lesions also weaken the FDP to digits 4-5. This is the "ulnar paradox." - Flexion of the elbow can weaken FCU and the FDP to digits 4 and 5 in proximal lesions, which causes radial deviation of the wrist on flexion.

**Diagnosis:** Diagnosis is mainly clinical. Useful tests are the Tinel sign over the cubital tunnel and the elbow flexion test, which reproduces symptoms within 1 to 3 minutes. Electrodiagnostic studies (NCS/EMG) show slowed conduction velocity across the elbow, with conduction block or reduced amplitude in more severe cases. Imaging (X-ray, ultrasound, MRI) is used for structural causes. Cervical radiculopathy (C8), thoracic outlet syndrome, and Guyon canal syndrome need to be excluded.

**Management:** - Conservative (mild or intermittent cases): avoid prolonged elbow flexion and pressure on the elbow, use night splinting or an elbow pad to keep the elbow in extension (about 45°), and consider NSAIDs and nerve gliding exercises. - Surgical (for refractory cases, motor weakness, or atrophy): in situ decompression, anterior transposition (subcutaneous or submuscular), or medial epicondylectomy.

**High-yield boards points:** - Ulnar nerve injury at the elbow causes weakness of FCU, FDP to digits 4-5, hypothenar muscles, the interossei, the medial two lumbricals, and adductor pollicis. - It spares the thenar muscles (median nerve, except adductor pollicis). - Do not confuse it with Guyon canal (wrist) syndrome, in which the dorsal hand sensation and FCU are spared. Cyclists (handlebar palsy) are a classic example of Guyon canal syndrome. - Do not confuse it with a lesion of the medial epicondyle fracture (classic for ulnar nerve injury in children). - Medial epicondylitis (golfer's elbow) is a different condition, but the two can coexist.