A 45-year-old man presents to the orthopedic clinic 8 weeks after sustaining a Colles fracture of his right wrist from a fall at work. He was treated with closed reduction and immobilization in a plaster cast. On examination, he has regained wrist mobility but now complains of sudden loss of thumb interphalangeal (IP) joint extension. Radiographs show evidence of good fracture healing with callus formation. What is the most likely complication?

Explanation

## Diagnosis: Extensor Pollicis Longus (EPL) Tendon Rupture **Key Point:** EPL rupture is a late complication of Colles fracture occurring 6–12 weeks post-injury, presenting with loss of thumb IP joint extension (inability to perform thumb 'thumbs up' sign). ### Pathophysiology ```mermaid flowchart TD A[Colles Fracture]:::outcome --> B[Fracture Healing & Callus Formation]:::outcome B --> C[EPL Tendon Friction Against Callus]:::action C --> D[Ischemic Necrosis of EPL]:::action D --> E[Tendon Rupture]:::urgent E --> F[Loss of Thumb IP Extension]:::outcome ``` **High-Yield:** EPL rupture occurs due to: 1. Mechanical friction of the tendon against the rough fracture callus 2. Ischemic necrosis from compromised blood supply 3. Attrition from rubbing against the dorsal surface of the distal radius ### Clinical Features | Feature | EPL Rupture | PIN Palsy | AIN Syndrome | |---------|-------------|-----------|---------------| | **Onset** | 6–12 weeks post-injury (late) | Acute (at time of injury) | Acute | | **Thumb IP Extension** | Lost | Preserved (EPL intact) | Preserved | | **Wrist Extension** | Preserved | Lost (all extensors) | Preserved | | **Finger Extension** | Preserved (2–5) | Lost (2–5) | Preserved | | **Forearm Pronation** | Preserved | Preserved | Preserved | | **Thumb IP Flexion** | Preserved | Preserved | **Lost** | **Clinical Pearl:** The loss of thumb IP extension is isolated and specific — the patient cannot perform the 'thumbs up' sign or extend the thumb IP joint against gravity. Wrist and finger extension remain intact, distinguishing this from PIN palsy. ### Mechanism of EPL Rupture 1. **Fracture healing** produces a rough callus on the dorsal surface of the distal radius 2. **EPL tendon** runs in the third dorsal compartment at the wrist, passing directly over the dorsal radius 3. **Friction and attrition** occur as the healing callus rubs against the tendon 4. **Ischemic necrosis** develops from compromised blood supply and mechanical trauma 5. **Spontaneous rupture** occurs, typically 6–12 weeks post-injury **Mnemonic:** **EPL-RUPTURE** = **E**xtensor **P**ollicis **L**ongus, **R**upture **U**sually **P**ost-fracture (6–12 wks), **T**humb **I**P extension **L**ost, **U**sually from **R**ough callus **E** [cite:Rockwood & Green's Fractures in Adults 9e Ch 18] ### Management 1. **Diagnosis:** Clinical assessment (loss of thumb IP extension) + imaging to confirm fracture healing 2. **Surgical repair:** Extensor indicis proprius (EIP) to EPL transfer (most common) - EIP is expendable (index finger has EDC for extension) - Provides functional thumb IP extension - Performed 3–4 months post-fracture to allow inflammation to resolve 3. **Alternative:** Flexor pollicis longus (FPL) to EPL transfer if EIP unavailable **Warning:** Do NOT confuse EPL rupture with PIN palsy — PIN injury occurs acutely at the time of fracture and affects all wrist and finger extensors, not just thumb IP extension. [cite:Rockwood & Green's Fractures in Adults 9e Ch 18]