A 35-year-old woman presents 6 weeks after a FOOSH injury with persistent wrist pain, swelling, and clicking. Repeat radiographs at 2 weeks showed a non-displaced fracture of the scaphoid waist. She was immobilized in a thumb spica cast for 4 weeks but removed it early due to discomfort. On current examination, anatomical snuffbox tenderness persists, and there is mild loss of grip strength. What is the most likely complication, and what is the appropriate imaging to assess it?

Explanation

## Complication Risk & Pathophysiology **Key Point:** Early removal of immobilization in scaphoid fractures significantly increases the risk of **nonunion** and **avascular necrosis (AVN)**. The scaphoid has a retrograde blood supply (distal to proximal), making the proximal pole vulnerable to AVN if immobilization is inadequate. **High-Yield:** Scaphoid waist fractures carry a 10–12% nonunion rate even with appropriate immobilization. Early cast removal dramatically increases this risk. At 6 weeks with persistent symptoms despite previous immobilization, nonunion is the most likely complication. ## Why Nonunion Occurs 1. **Inadequate immobilization** — early cast removal allows micromotion at the fracture site. 2. **Scaphoid waist location** — waist fractures have intermediate blood supply and higher nonunion rates than distal pole fractures. 3. **Time frame** — 6 weeks is insufficient for complete union in scaphoid fractures (typically 8–12 weeks required). ## Imaging Hierarchy for Suspected Nonunion | Imaging | Sensitivity | Specificity | Use | |---------|-------------|-------------|-----| | **Plain radiographs** | 70–80% | Moderate | Initial assessment; may miss early nonunion | | **CT scan** | 95%+ | Excellent | Gold standard for assessing union status and fracture gap | | **MRI** | 95%+ | Excellent | Assesses vascularity of proximal pole (T2 signal = perfusion) | | **Ultrasound** | Variable | Low | Not reliable for scaphoid nonunion | **Clinical Pearl:** Persistent anatomical snuffbox tenderness at 6 weeks with a history of early cast removal is a red flag for nonunion. CT or MRI should be obtained urgently to guide further management (prolonged immobilization vs. surgical fixation). ## Management of Nonunion ```mermaid flowchart TD A[Scaphoid Nonunion Suspected]:::outcome --> B{CT/MRI confirms nonunion?}:::decision B -->|Yes| C{Proximal pole AVN present?}:::decision C -->|No AVN| D[Prolonged immobilization 6-12 weeks]:::action C -->|AVN present| E[Surgical fixation ± bone graft]:::action B -->|No| F[Continue immobilization & repeat imaging]:::action D --> G[Repeat imaging to confirm union]:::action E --> H[Vascularized bone graft if severe AVN]:::action ``` **Mnemonic: SCAPHOID NONUNION RISK FACTORS** — **S**waist location, **C**ast removed early, **A**vascular supply compromised, **P**roximal pole involvement, **H**igh-energy injury, **O**lder age, **I**nadequate immobilization, **D**iabetes.