A 55-year-old man from Mumbai falls directly on the dorsum of his flexed right wrist while trying to break his fall. He presents with wrist pain, swelling, and a 'reverse dinner fork' deformity on clinical examination. X-ray shows a transverse fracture of the distal radius with volar displacement and volar angulation of the distal fragment. The patient is concerned about loss of wrist extension. Which nerve is at highest risk of acute compression injury in this fracture pattern?

Explanation

## Diagnosis: Smith Fracture with Median Nerve Compression Risk ### Fracture Identification: Smith Fracture **Key Point:** Smith fracture is a transverse fracture of the distal radius with **volar (palmar) displacement and volar angulation** of the distal fragment, creating a 'reverse dinner fork' deformity. ### Clinical Presentation - **Mechanism:** Fall on flexed wrist or direct blow to dorsum of wrist - **Deformity:** Reverse dinner fork (volar prominence) - **Associated findings:** Often more unstable than Colles; higher risk of complications ### Comparison: Colles vs Smith Fractures | Feature | Colles | Smith | |---------|--------|-------| | **Displacement** | Dorsal | **Volar** | | **Angulation** | Dorsal | **Volar** | | **Deformity** | Dinner fork | **Reverse dinner fork** | | **Mechanism** | FOOSH (extension) | **FOOSH (flexion) / Direct blow** | | **Stability** | Relatively stable | More unstable | | **Nerve risk** | Carpal tunnel (median) | **Carpal tunnel (median)** | ### Nerve Injury Risk in Smith Fracture **High-Yield:** Smith fractures carry a **higher risk of median nerve compression** than Colles fractures because: 1. Volar displacement of the distal fragment narrows the carpal tunnel 2. Swelling and hematoma in the volar wrist compress the median nerve 3. Acute carpal tunnel syndrome can develop within hours **Clinical Pearl:** Median nerve compression presents with: - Paresthesias in thumb, index, middle, and radial half of ring finger - Weakness of thumb opposition (recurrent motor branch) - Loss of sensation in median nerve distribution - Positive Phalen test (if chronic) ### Why Other Nerves Are Not at Risk | Nerve | Location | Risk in Smith | |-------|----------|---------------| | **AIN** | Arises from median nerve distal to elbow; runs deep in forearm | Low risk; injury rare unless associated with proximal radius fracture | | **PIN** | Dorsal wrist; winds around proximal radius | Low risk; dorsal displacement would threaten PIN, not volar | | **Radial nerve (spiral groove)** | Mid-shaft humerus | Not relevant to distal radius fracture | **Mnemonic:** **VOLAR Smith = Median nerve at risk** - **V**olar displacement → narrows carpal tunnel - **O**utcomes include median nerve compression - **L**oss of thumb opposition (recurrent motor branch) - **A**cute carpal tunnel syndrome - **R** = Reverse dinner fork ### Management Implications 1. **Immediate:** Assess median nerve function (motor and sensory) 2. **Reduction:** Urgent reduction to decompress carpal tunnel if signs of compression 3. **Monitoring:** Serial neurological exams; consider early decompression if symptoms persist 4. **Imaging:** CT or MRI if nerve injury suspected [cite:Rockwood and Green's Fractures in Adults Ch 17]