Peripheral Nerve Injuries: Wrist Drop, Foot Drop, Claw Hand - Orthopaedic Prof Guide

CLASSIFICATION OF NERVE INJURY (Seddon & Sunderland)

1. WRIST DROP (Drop Hand) - Radial Nerve Injury

Wrist drop / claw deformity from nerve injury

Nerve: Radial Nerve (C5-C8)

Mechanism of Deformity

Causes by Level

• Improperly adjusted crutches
• Fracture-dislocation of upper end of humerus
• Features: Wrist drop + loss of triceps (cannot extend elbow) + full sensory loss

• Fracture of shaft of humerus (most classic for ortho exams)
• Sleeping with arm hanging over bench/chair
• Pressure at edge of operating table
• Inadvertent intramuscular injection
• Features: Wrist drop without triceps involvement (triceps branches exit before the groove) + sensory loss over first web space dorsum

• Chronic compression
• Features: Wrist drop without triceps loss

• Fracture/dislocation of upper end of radius
• Features: Motor loss only (no wrist drop paradox - ECRB is spared), NO sensory loss

Clinical Findings (Motor)

• Unable to extend wrist
• Unable to extend MCPJs of fingers
• Brachioradialis test: Forearm in mid-prone position, flex elbow against resistance - muscle fails to stand out if radial nerve injured above its branching

Clinical Findings (Sensory)

• Sensory loss on the radial surface of the dorsum of the hand
• Extensor surface of thumb, index finger, and radial half of middle finger (up to PIP joint)
• Autonomous zone (exclusive territory): First dorsal web space (between thumb and index finger)

Brachioradialis Test (Level Determination)

2. FOOT DROP - Common Peroneal (Lateral Popliteal) Nerve Injury

Nerve: Common Peroneal Nerve (L4, L5, S1)

Mechanism of Deformity

Common Causes

• Fracture neck of fibula (most classic for ortho exams - nerve winds around the fibular neck)
• Prolonged squatting or crossed-leg sitting (pressure at fibular head)
• Plaster cast too tight at fibular head
• Knee dislocations (lateral aspect)
• Car bumper injury (classic trauma mechanism)

Deformity

• Equinovarus (foot drops and turns inward)
• Patient cannot dorsiflex or evert the foot
• High stepping (steppage) gait to clear the ground

Clinical Findings (Motor)

Clinical Findings (Sensory)

• Loss over anterior and lateral aspects of the leg
• Entire dorsum of the foot and toes (except the first web space between 1st and 2nd toes - supplied by deep peroneal nerve)
• Autonomous zone: First web space of dorsum of foot (deep peroneal branch)

Treatment (Ortho)

• Conservative: AFO (ankle-foot orthosis) - splint the foot in neutral
• Tendon transfer (if permanent): Transfer of PTT (posterior tibial tendon) through the interosseous membrane to the dorsal midfoot to restore dorsiflexion. Also requires TAL (tendoachilles lengthening).

3. CLAW HAND (Main en Griffe) - Ulnar ± Median Nerve Injury

Nerve: Ulnar Nerve (C8, T1) - primary; also Median Nerve (C6-T1)

Mechanism of Deformity

• Flexion of MCPJs
• Extension of IPJs through extensor expansions

• Extensor digitorum (unopposed) hyperextends the MCPJs
• FDS and FDP (unopposed) flex the IPJs
• Result: Hyperextension at MCP + Flexion at PIP + DIP = Claw

• The 1st and 2nd lumbricals (for index and middle) are supplied by the median nerve and can partially compensate
• 3rd and 4th lumbricals (ring and little) are ulnar-supplied → these 2 fingers claw more = Ulnar Paradox: a more proximal lesion (at elbow) also paralyzes FDP to the ring and little fingers, which partially reduces the clawing. A distal wrist lesion produces a more severe claw.

Causes by Level

• Supracondylar fracture (recent injury or late tardy ulnar palsy from callus/cubitus valgus)
• Fracture medial epicondyle
• Cubital tunnel syndrome (compression between flexor carpi ulnaris heads)
• Sulcus ulnaris syndrome (chronic traction)
• Features: Claw + sensory loss + FCU paralysis (hand deviates radially on flexion) + medial half FDP paralysis (ring/little finger profundus lost)

• Lacerations, Guyon's canal (ulnar tunnel) compression
• Features: Claw + sensory loss (no FCU involvement)

Clinical Findings (Motor)

Clinical Findings (Sensory)

• Medial side of the hand
• Entire little finger (ring and little in some)
• Autonomous zone: Little finger (tip and medial border)
• Atrophy: Hypothenar eminence + interosseous spaces (first interosseous space most conspicuous)

4. OTHER IMPORTANT DEFORMITIES (for complete Prof exam)

Median Nerve Injury

• Ochsner's clasping test / Pointing index sign: When patient clasps hands, the index finger fails to flex (FDP lateral half paralyzed) - this is the "pointing index"
• FPL paralyzed: Cannot flex terminal phalanx of thumb
• FCR paralyzed: Hand deviates ulnar on wrist flexion

• Simian/Ape hand: Thenar muscles wasted; thumb comes to same plane as metacarpals; opposition lost
• Pen test (Abductor pollicis brevis): Lay hand flat, ask to touch pen held above palm - unable to do so
• Opponens pollicis: Cannot bring thumb tip to meet other fingertips

Combined Ulnar + Median Nerve Injury

• Produces maximum claw hand (all interossei + all 4 lumbricals lost)
• Also seen in Klumpke's paralysis (lower brachial plexus C8-T1)

5. QUICK REVISION TABLE FOR VIVA

6. KEY CLINICAL EXAMINATION POINTS (Prof OSCE)

1. Always look at the scar - the site of the wound tells you the likely nerve injured
2. Attitude and deformity on inspection is the first clinical clue
3. Test the "autonomous zone" for sensory loss - this is the most reliable area to confirm injury
4. Extension of IP joints in wrist drop = NOT radial nerve recovery - it is the interossei (ulnar nerve) acting through the extensor expansion (common viva trap)
5. Brachioradialis spared = injury is at/below lateral intermuscular septum (midlevel radial); if triceps lost = injury is above the radial groove (axilla)
6. Ulnar paradox: Distal ulnar lesion (wrist) = worse claw than proximal (elbow), because FDP is still intact distally
7. Froment's sign is the single best bedside test for adductor pollicis (ulnar nerve)
8. Saturday night palsy = radial nerve compressed in the spiral groove - wrist drop without triceps loss, good prognosis