A 58-year-old woman with osteoporosis presents 8 weeks after a minimally displaced fracture of the surgical neck of the humerus treated conservatively with a sling. She reports persistent shoulder pain and stiffness. Radiographs show no callus formation and the fracture line remains clearly visible with no bridging bone. What is the most likely diagnosis and its primary risk factor in this case?

Explanation

## Nonunion vs. Delayed Union: Pathophysiology and Classification ### Diagnostic Criteria for Nonunion **Key Point:** Nonunion is defined as a fracture that has not healed after 6 months OR shows no radiographic evidence of healing for 3 consecutive months. This patient is at 8 weeks with: - No callus formation - Persistent fracture line - No bridging bone These findings indicate nonunion is already developing, not merely delayed union. ### Classification of Nonunion ```mermaid flowchart TD A[Nonunion]:::outcome --> B{Radiographic<br/>appearance?}:::decision B -->|Hypertrophic:<br/>bulbous callus| C[Adequate blood supply<br/>Poor mechanical stability]:::outcome B -->|Atrophic:<br/>no callus| D[Poor blood supply<br/>Poor bone quality]:::outcome C --> E[Causes: inadequate<br/>immobilization, motion]:::outcome D --> F[Causes: osteoporosis,<br/>age, comorbidities]:::outcome E --> G[Rx: rigid fixation]:::action F --> H[Rx: bone graft +<br/>rigid fixation]:::action ``` ### Why This Patient Has Atrophic Nonunion **High-Yield:** Atrophic nonunion occurs when bone quality is poor (osteoporosis) and/or blood supply is compromised. The surgical neck of the humerus has a precarious blood supply; combined with osteoporosis, this creates a hostile environment for healing: 1. **Osteoporosis** = reduced bone mineral density, impaired osteoblast function, and poor callus formation 2. **Surgical neck location** = vulnerable to vascular compromise (the anterior circumflex humeral artery is the main blood supply) 3. **Conservative treatment (sling)** = some micromotion, but in osteoporotic bone, this is insufficient to stimulate healing ### Atrophic vs. Hypertrophic Nonunion | Feature | Atrophic | Hypertrophic | |---------|----------|-------------| | **Callus formation** | Absent or minimal | Abundant, bulbous | | **Fracture line** | Clearly visible, sclerotic edges | Obscured by callus | | **Blood supply** | Poor | Adequate | | **Bone quality** | Poor (osteoporosis, age, comorbidity) | Usually good | | **Primary cause** | Vascular insufficiency, poor bone stock | Inadequate immobilization, motion | | **Treatment** | Bone graft + rigid fixation | Rigid fixation (compression plating) | | **Prognosis** | Slower healing; higher failure rate | Good with rigid fixation | ### Clinical Pearl **Osteoporosis is a major risk factor for nonunion**, particularly in elderly women. Fractures in osteoporotic bone heal more slowly and incompletely because: - Osteoblasts are dysfunctional - Callus formation is impaired - Bone resorption exceeds formation - Vascularity is often compromised ### Why Delayed Union Does Not Fit **Warning:** Delayed union is defined as healing that takes longer than expected (typically >3–4 months for most fractures) but eventually heals with appropriate treatment. This patient shows NO radiographic evidence of healing at 8 weeks — no callus, persistent fracture line. This is nonunion, not delayed union. ### Management of Atrophic Nonunion 1. **Rigid internal fixation** (compression plating, intramedullary nailing) 2. **Autologous bone graft** (gold standard) or allograft 3. **Biological enhancement** (BMP, PRP) in selected cases 4. **Address osteoporosis** (calcium, vitamin D, bisphosphonates) **Tip:** The surgical neck of the humerus is a notorious site for nonunion; proximal humerus fractures in elderly osteoporotic patients require careful attention to vascular supply and often benefit from early surgical fixation rather than conservative treatment.