A 6-year-old girl presents to the orthopedic clinic 3 days after sustaining a supracondylar fracture of the humerus (Gartland type II) managed with closed reduction and posterior slab immobilization in the emergency department. On examination, she has weakness of wrist and finger extension but normal sensation in the first web space. Grip strength is 2/5 on the affected side. What is the most likely nerve injury, and what is the recommended management?

Explanation

## Nerve Injuries in Supracondylar Fracture: Diagnosis and Management ### Clinical Presentation Analysis **Key Point:** Weakness of **wrist and finger extension** with **intact sensation in the first web space** localizes the injury to the **posterior interosseous nerve (PIN)**, not the anterior interosseous nerve (AIN) or median nerve. ### Anatomical Correlation | Nerve | Motor Function | Sensory | Clinical Test | |-------|---|---|---| | **Posterior Interosseous Nerve (PIN)** | Wrist extension, finger extension (EDC, EIP) | None (purely motor) | Loss of wrist/finger extension | | **Anterior Interosseous Nerve (AIN)** | Thumb IP flexion, index DIP flexion | None (purely motor) | Loss of thumb IP and index DIP flexion | | **Radial Nerve (proximal)** | Wrist extension, finger extension, thumb abduction | Dorsal first web space | Loss of wrist/finger extension + sensory loss | | **Median Nerve** | Wrist/finger flexion, thumb opposition | Lateral palm, thumb, index | Loss of grip, opposition | **High-Yield:** The **first web space sensation is NORMAL** — this rules out radial nerve injury (which causes sensory loss in the dorsal first web space). ### Why PIN and Not AIN? - **PIN injury** → loss of **wrist and finger extension** (EDC, EIP muscles). - **AIN injury** → loss of **thumb IP flexion** and **index DIP flexion** (FPL, FDP-II muscles) — no wrist or finger extension loss. This patient has wrist/finger extension weakness, so **PIN is the diagnosis**. ### Management of Nerve Injuries in Supracondylar Fracture ```mermaid flowchart TD A[Supracondylar fracture + nerve injury]:::outcome --> B{Timing of injury recognition?}:::decision B -->|Immediate post-reduction| C{Nerve type?}:::decision B -->|Delayed discovery| D[Observe 8-12 weeks]:::action C -->|PIN/AIN/Radial| E[Observe 8-12 weeks]:::action C -->|Median/Ulnar| F[Observe 8-12 weeks]:::action E --> G{Recovery at 12 weeks?}:::decision G -->|Yes| H[Full recovery expected]:::outcome G -->|No| I[EMG/NCS + consider exploration]:::action ``` **Clinical Pearl:** Nerve injuries in supracondylar fractures are usually **neurapraxias** (stretch injuries) and recover spontaneously in 80–90% of cases. **Observation for 8–12 weeks is the standard of care** for all nerve injuries in this setting, unless there is: - Nerve transection (rare in closed fractures). - Vascular injury requiring exploration (which may incidentally identify nerve injury). - Failure to recover by 12 weeks (then EMG/NCS and possible exploration). ### Why Observation? 1. Most injuries are stretch-related (neurapraxia), not transection. 2. Spontaneous recovery occurs in >80% by 8–12 weeks. 3. Immediate exploration risks further soft tissue trauma. 4. EMG/NCS at 3 weeks can help prognosticate, but does not change acute management. [cite:Rockwood & Green's Fractures in Adults 9e Ch 11]