A 42-year-old labourer presents with a fracture of the femoral shaft sustained 4 months ago. Clinical examination shows minimal callus formation and radiographs reveal a persistent fracture line with no bridging bone. Which of the following is the most common cause of non-union in this patient?

Explanation

## Non-Union in Fracture Healing **Key Point:** Non-union occurs when fracture healing ceases before bony union is achieved, typically diagnosed at 6–9 months post-injury with radiological evidence of a persistent fracture line and no progression toward healing. In **closed** fractures of the femoral shaft, soft tissue interposition is the most commonly cited primary mechanical cause. ### Most Common Cause in Closed Fractures: Soft Tissue Interposition Excessive soft tissue interposition (muscle, fascia, periosteum, or fibrous tissue) between fracture fragments is the **most frequent mechanical cause of non-union in closed long-bone fractures**, including the femoral shaft. This physical barrier prevents direct contact of bone ends and blocks the formation of a bridging callus, resulting in the atrophic or oligotrophic pattern seen on radiographs. **High-Yield:** Non-union is classified as: - **Hypertrophic non-union:** Abundant callus formation but no bridging (typically due to inadequate immobilization) - **Atrophic non-union:** Minimal callus, poor vascular supply, or mechanical barrier (e.g., soft tissue interposition) — the pattern described in this vignette ### Causes of Non-Union: Frequency and Mechanism | Cause | Mechanism | Context | Relative Frequency | | --- | --- | --- | --- | | **Soft tissue interposition** | Mechanical barrier blocks bone contact | Closed femoral/humeral shaft fractures | **Most common (closed fractures)** | | Infection | Osteomyelitis, chronic suppuration | Open fractures, post-surgical | Common in open fractures | | High-energy injury | Comminution, vascular disruption | High-velocity trauma | Moderate | | Poor nutrition/smoking | Impaired osteoblast function, angiogenesis | Systemic/metabolic | Contributory, not primary | > **Important distinction:** Infection is the most common cause of non-union in **open fractures** and post-operative cases. In **closed fractures** (as implied by this vignette — no mention of open wound or surgery), soft tissue interposition is the primary mechanical culprit. Smoking and poor nutrition are systemic risk factors that contribute to delayed union but are not the single most common primary cause. (Reference: Rockwood & Green's Fractures in Adults, 9th ed.; Campbell's Operative Orthopaedics, 14th ed.) **Clinical Pearl:** Femoral shaft fractures have a non-union rate of approximately 5–10%. Anatomic reduction and stable fixation (intramedullary nail or plate) are critical to prevent soft tissue from interposing between fragments. When non-union is identified, surgical debridement of interposed tissue combined with bone grafting and rigid fixation is the standard approach. ### Management Approach ``` Suspected Non-Union (closed femoral shaft fracture) → Confirm radiologically (persistent fracture line, no bridging callus) → Identify cause: soft tissue interposition (most common in closed fractures) → Treatment: Surgical debridement of interposed tissue + bone grafting + rigid fixation (IM nail) → Adjuncts: Optimize nutrition, smoking cessation, consider electrical stimulation ``` **Tip:** In a closed femoral shaft fracture presenting with atrophic non-union at 4+ months, always suspect soft tissue interposition as the primary mechanical cause — this directly guides the surgical approach requiring careful dissection and removal of intervening tissue before fixation.