ulnar claw

**Deformity:** Hyperextension at the 4th and 5th metacarpophalangeal (MCP) joints, with flexion at the proximal and distal interphalangeal (PIP/DIP) joints. The ring and little fingers curl into a "claw."

**Pathophysiology:** - The medial two lumbricals (to digits 4 and 5) are supplied by the deep branch of the ulnar nerve (C8-T1). Lumbricals flex the MCP and extend the IP joints. - With the lumbricals paralyzed, the extensor digitorum hyperextends the MCP joints unopposed. The flexor digitorum profundus (FDP) and superficialis flex the IP joints unopposed. - The interossei (also ulnar) are lost as well, which worsens the loss of MCP flexion and IP extension. - The index and middle fingers are spared because the lateral two lumbricals are supplied by the median nerve.

**Ulnar paradox:** - A LOW lesion (wrist, Guyon canal) leaves the ulnar half of the FDP intact. The claw is therefore MORE prominent because of strong, unopposed IP flexion. - A HIGH lesion (elbow, e.g., cubital tunnel or medial epicondyle fracture) also paralyzes the ulnar half of the FDP (digits 4 and 5). The claw is therefore LESS prominent, but there is more sensory and motor loss, including weak wrist flexion with radial deviation.

**Associated findings in ulnar neuropathy:** - Loss of sensation over the medial 1½ digits (palmar and dorsal for lesions at the elbow or proximal wrist). - Hypothenar atrophy, interosseous wasting, and a hollowed dorsal first web space. - Froment sign: the patient substitutes the flexor pollicis longus (median nerve) for the weak adductor pollicis (ulnar), so the thumb IP joint flexes when gripping paper. - Wartenberg sign: persistent abduction of the 5th digit from unopposed extensor digiti minimi. - Weak finger abduction and adduction (the "crossed fingers" test). - Card test: weak adduction of the fingers.

**Causes:** - Elbow: cubital tunnel syndrome (most common site of entrapment), medial epicondyle fracture, "funny bone" trauma. - Wrist: Guyon canal compression (cyclists, "handlebar palsy"), fracture of the hook of the hamate. - Other: leprosy, diabetes, and trauma. Klumpke palsy (C8-T1 lower trunk or root injury) can also produce a claw hand, but with additional median-innervated deficits.

**Contrast with "hand of benediction":** This is a median nerve lesion where the patient attempts to make a fist. The index and middle fingers fail to flex while the ring and little fingers flex normally. It is easily confused with the ulnar claw on exams.

**Management:** - Conservative: avoid elbow flexion and pressure, splinting, and NSAIDs. - Surgical: decompression or ulnar nerve transposition for refractory cases. - Diagnosis: clinical, supported by EMG/nerve conduction studies.

**High-yield pearl:** Ulnar claw = ulnar nerve ("ulnar nerve = claw"). Median nerve = ape hand / hand of benediction. Radial nerve = wrist drop.