A 58-year-old woman with osteoporosis sustained a fall from standing height and sustained a fracture of the proximal humerus. Radiographs show a 2-part fracture of the surgical neck with minimal displacement. She is treated conservatively with a sling and pendulum exercises. At 8 weeks follow-up, radiographs show no callus formation and the fracture line remains clearly visible. The patient reports persistent pain and minimal functional improvement. Which of the following is the most likely complication?

Explanation

## Nonunion of Proximal Humerus Fracture ### Definition and Pathophysiology **Key Point:** Nonunion is defined as failure of fracture healing after 6 months, or absence of radiographic evidence of callus formation at 8–12 weeks. In this case, at 8 weeks with no callus and persistent fracture line visibility, nonunion is developing. ### Risk Factors for Nonunion in Proximal Humerus Fractures | Risk Factor | Mechanism | |-------------|----------| | Advanced age (>60 years) | Reduced bone turnover, poor healing capacity | | Osteoporosis | Compromised bone quality, poor fracture stability | | Surgical neck fractures | Tenuous blood supply to proximal fragment | | Displacement >1 cm | Increased strain at fracture site | | Inadequate immobilization | Excessive micromotion inhibits callus formation | | Smoking, poor nutrition | Impaired angiogenesis and osteoblast function | **High-Yield:** Nonunion rates in proximal humerus fractures range from 5–10% overall, but rise to 15–20% in elderly patients with osteoporosis treated conservatively. ### Clinical and Radiographic Features of Nonunion 1. **Persistent pain** beyond expected healing timeline (8–12 weeks) 2. **No callus formation** on serial radiographs 3. **Fracture line remains sharp and clearly visible** (not bridged by bone) 4. **Minimal functional improvement** despite therapy 5. **Possible pseudarthrosis** (false joint formation with fibrocartilage) **Clinical Pearl:** The absence of callus at 8 weeks in a proximal humerus fracture is an early warning sign. Intervention at this stage (before true nonunion is established) can prevent progression to established nonunion. ### Why Nonunion Occurs in This Case ```mermaid flowchart TD A[58-year-old woman with osteoporosis]:::outcome A --> B[Proximal humerus fracture]:::outcome B --> C[Conservative management with sling]:::action C --> D{Adequate blood supply?}:::decision D -->|Compromised| E[Reduced osteoblast recruitment]:::outcome D -->|Adequate| F[Normal healing pathway]:::action E --> G[Minimal callus formation]:::outcome G --> H[Nonunion at 8-12 weeks]:::urgent F --> I[Callus visible by 4-6 weeks]:::outcome I --> J[Union by 12-16 weeks]:::action ``` **Mnemonic:** **NONUNION** — **N**o callus at **O**lder age, **N**eck fractures, **U**nstable positioning, **N**utrition poor, **I**nadequate immobilization, **O**steoporosis, **N**egligible blood supply. ### Management of Nonunion 1. **Early intervention (8–12 weeks):** Consider operative fixation (open reduction internal fixation with plate, or intramedullary nail) before true nonunion is established 2. **Biological augmentation:** Bone graft (autograft or allograft) to improve healing potential 3. **Optimize conditions:** Smoking cessation, nutritional support, vitamin D supplementation 4. **Electrical stimulation:** May enhance osteogenesis in select cases ### Why Other Options Are Wrong **Avascular necrosis (AVN):** - AVN typically manifests at 6–12 months post-fracture, not at 8 weeks - Radiographic signs (crescent sign, collapse) appear later - The clinical presentation (no callus, sharp fracture line) is more consistent with nonunion than AVN - AVN is more common in 4-part fractures and displaced 3-part fractures, not 2-part surgical neck fractures **Myositis ossificans:** - Presents as heterotopic bone formation in soft tissues (visible on radiographs as radiopaque masses) - Not associated with absent callus formation or persistent fracture line visibility - Causes pain and stiffness but not fracture nonunion - Rare complication of proximal humerus fractures **Posterior dislocation:** - Would present with obvious loss of normal humeral head position on radiographs - Associated with severe pain and loss of external rotation - Not consistent with a 2-part fracture with minimal displacement - Would be evident immediately, not a delayed finding [cite:Rockwood & Green's Fractures in Adults 9e Ch 10; Orthopedic Trauma Association Guidelines on Proximal Humerus Fractures]