A 6-year-old girl presents to the orthopedic clinic 3 days after a supracondylar fracture of the right humerus that was treated with closed reduction and posterior splinting in the emergency department. The fracture was initially well-reduced on X-ray. On re-examination today, she has loss of thumb interphalangeal (IP) joint flexion and weakness of index finger distal interphalangeal (DIP) joint flexion. Radial pulse is palpable and hand perfusion is normal. What is the most likely nerve injury and what is the appropriate management?

Explanation

## Anterior Interosseous Nerve (AIN) Injury in Supracondylar Fractures ### Clinical Presentation The patient has: - **Loss of thumb IP flexion** (flexor pollicis longus — FPL) - **Weakness of index finger DIP flexion** (flexor digitorum profundus to index — FDP-I) This is the **classic presentation of AIN injury**. ### Nerve Injury Patterns in Supracondylar Fractures | Nerve | Incidence | Clinical Findings | Mechanism | |-------|-----------|-------------------|----------| | **AIN (branch of median)** | 10–15% (most common) | Loss of thumb IP flexion, index DIP flexion | Traction, compression by fracture fragments | | Radial nerve | 5–10% | Wrist drop, dorsal hand sensory loss | Posterior displacement of proximal fragment | | Median nerve proper | 5% | Sensory loss palm/fingers 1–3, weak pronation | Direct trauma, traction | | Ulnar nerve | 2–5% | Claw hand deformity, medial hand sensory loss | Rare; usually iatrogenic with pinning | ### High-Yield Facts: **Key Point:** - **AIN is the most common nerve injury** in supracondylar fractures - AIN is a **pure motor nerve** — there is **no sensory loss** - Most nerve injuries in supracondylar fractures are **neuropraxias** and recover spontaneously **Mnemonic for AIN motor loss: "FPL-FDP-I"** - **F**lexor **P**ollicis **L**ongus (thumb IP flexion) - **F**lexor **D**igitorum **P**rofundus to **I**ndex (index DIP flexion) ### Management Algorithm ```mermaid flowchart TD A[Supracondylar fracture + nerve injury]:::outcome --> B{Timing of nerve injury}:::decision B -->|Immediate post-reduction| C[Likely neuropraxia from traction]:::outcome B -->|Delayed onset| D[Likely compression/entrapment]:::outcome C --> E[Observation for 3 months]:::action D --> F[Consider EMG/NCS at 3-4 weeks]:::action E --> G{Recovery by 3 months?}:::decision G -->|Yes| H[Continue observation]:::action G -->|No| I[EMG/NCS + consider surgical exploration]:::action ``` ### Clinical Pearl: - **Immediate nerve injuries** (present at time of reduction) are usually **neuropraxias** from traction and recover spontaneously in 60–90% of cases - **Delayed nerve injuries** (appearing days to weeks later) suggest entrapment or compression and may require surgical intervention - This patient's injury is **immediate post-reduction**, suggesting neuropraxia ### Appropriate Management: 1. **Observation for 3 months** with serial neurological examination 2. Document baseline motor deficits 3. Repeat examination at 6 weeks and 3 months 4. If no improvement by 3 months → EMG/NCS and consider surgical exploration 5. Most AIN injuries recover fully within 3 months without intervention ### Why NOT Immediate Surgery? - No evidence of complete nerve transection (fracture was reduced) - Neuropraxias recover spontaneously in the majority of cases - Immediate exploration adds morbidity without proven benefit - Standard practice is to observe for 3 months before considering surgery [cite:Campbell's Operative Orthopaedics 13e Ch 54; Rockwood & Green's Fractures in Adults 9e Ch 47]