cubital tunnel

**Anatomy** - Location: posterior to the medial epicondyle and medial to the olecranon. - Roof: the cubital tunnel retinaculum (Osborne's ligament/fascia), which tightens with elbow flexion. In some people the anconeus epitrochlearis muscle replaces it. - Floor: the medial collateral ligament of the elbow and the joint capsule. - Proximal continuation: the arcade of Struthers, about 8 cm proximal to the medial epicondyle, is another compression site. - Distal continuation: the ulnar nerve passes between the two heads of flexor carpi ulnaris (FCU) and under the aponeurosis (Osborne's band). - Contents: the ulnar nerve (C8–T1), the posterior ulnar recurrent artery and the superior ulnar collateral artery. - The "funny bone" is the ulnar nerve at the medial epicondyle (the ulnar groove).

**Pathophysiology** - With elbow flexion, the tunnel volume shrinks, the retinaculum tightens and the nerve stretches. Intraneural pressure rises, which causes ischemia and demyelination. - Causes: prolonged or repeated elbow flexion (for example, sleeping with the elbows bent or holding a phone), leaning on the elbow, trauma or fracture (especially a supracondylar or medial epicondyle fracture, with late "tardy ulnar palsy" from cubitus valgus), osteoarthritis or osteophytes, ganglion cysts, ulnar nerve subluxation, and anconeus epitrochlearis.

**Clinical features** - Sensory: paresthesias and numbness of the little finger and the medial half of the ring finger, including the dorsal ulnar hand. The dorsal ulnar hand is spared in Guyon canal syndrome, because the dorsal cutaneous branch arises about 5 cm proximal to the wrist. - Motor: weak grip and pinch, and clumsiness. - Interossei and the medial two lumbricals are affected. This produces a **claw hand** (ulnar claw, hyperextension of the MCP joints and flexion of the IP joints of digits 4–5). It is more pronounced with lesions at the wrist than at the elbow, which is the "ulnar paradox." In an elbow lesion the FCU and the ulnar half of FDP are also weak, so there is less clawing. - **Froment sign**: weak adductor pollicis, so the patient substitutes flexor pollicis longus (median nerve) and flexes the thumb IP joint when pinching paper. - **Wartenberg sign**: abducted little finger from weak palmar interossei. - Hypothenar and first dorsal interosseous wasting in late disease. - Crossed-finger and "Jeanne sign" (thumb MCP hyperextension) may also appear. - Provocative tests: Tinel sign over the cubital tunnel, elbow flexion test (maximal flexion for 1–3 minutes reproduces symptoms), and pressure provocation test.

**Diagnosis** - Clinical diagnosis, supported by EMG/NCS. Slowed conduction velocity across the elbow (<50 m/s) or a drop in conduction across the elbow segment is typical. - Imaging (X-ray, ultrasound or MRI) can look for structural causes.

**Differential diagnosis** - Guyon canal (ulnar tunnel) syndrome at the wrist: dorsal hand sensation is spared, and FCU and FDP strength is normal. - C8–T1 radiculopathy. - Thoracic outlet syndrome (lower trunk of the brachial plexus). - Klumpke palsy. - Medial epicondylitis.

**Management** - Conservative (mild disease): avoid prolonged elbow flexion and pressure on the elbow, use night splinting or an elbow pad to keep the elbow extended, NSAIDs, and nerve gliding exercises. - Surgical (severe or refractory disease, or motor deficits and muscle wasting): in situ decompression, anterior transposition (subcutaneous or submuscular), or medial epicondylectomy.

**Boards pearls** - The ulnar nerve is the nerve of the cubital tunnel; the median nerve is in the carpal tunnel. - Do not confuse the *cubital fossa* (anterior elbow: median nerve, brachial artery, biceps tendon) with the cubital tunnel (posteromedial). - The ulnar nerve is the most commonly injured nerve in medial epicondyle fractures. - "Ulnar nerve = hand intrinsics + FCU + medial half of FDP." - A lesion at the elbow or proximal to it causes sensory loss that includes the dorsal ulnar hand. A lesion at the wrist (Guyon) spares the dorsal hand.