In the classification of fracture union complications, a fracture in which callus formation has ceased but bridging across the fracture site is incomplete is termed:

Explanation

## Non-Union: Definition & Classification ### Definition **Non-union** is a fracture in which the healing process has **ceased (arrested)** without complete bridging across the fracture site. The key distinguishing feature is that callus formation has **stopped progressing** — healing is no longer occurring. ### Key Characteristics | Feature | Delayed Union | Non-Union | Malunion | | --- | --- | --- | --- | | **Callus formation** | Present and progressing | Ceased / arrested | Present | | **Bridging** | Incomplete but still progressing | Incomplete and static | Complete but misaligned | | **Healing status** | Still healing (slow) | Healing arrested | Healed in wrong position | | **Time frame** | Beyond normal timeline | Typically >6 months, static | Healed but deformed | | **Treatment** | Conservative or surgical stimulation | Surgical (ORIF, bone grafting) | Surgical correction (osteotomy) | ### Critical Distinction: Delayed Union vs. Non-Union - **Delayed union**: Callus is present and **still forming/progressing**, but union is taking longer than expected. Healing is ongoing — just slow. - **Non-union**: Callus formation has **ceased**; bridging is incomplete and there is no radiological progression over serial X-rays (typically 3 months apart). This is the definition in the stem. ### Types of Non-Union (Müller/AO Classification) 1. **Hypertrophic non-union** ("elephant foot") — abundant callus, good vascularity, but no bridging; due to inadequate immobilization 2. **Atrophic non-union** — no callus, poor vascularity; due to avascular necrosis, infection, or bone loss 3. **Pseudarthrosis** — a subtype of non-union where a false joint (synovial cavity) forms at the fracture site ### Causes of Non-Union 1. Infection / osteomyelitis 2. Avascular necrosis / poor blood supply 3. Soft tissue interposition 4. Excessive distraction or bone loss 5. Inadequate immobilization 6. Systemic factors: diabetes, smoking, malnutrition, corticosteroids **Key Point:** The stem states "callus formation has **ceased** but bridging is incomplete" — this is the textbook definition of **non-union**, not delayed union. In delayed union, callus is still actively forming and progressing toward bridging. **High-Yield:** Per Rockwood & Green's Fractures in Adults and Campbell's Operative Orthopaedics, non-union is defined as a fracture in which the normal reparative process has stopped without achieving bony union. Serial radiographs showing no progression over 3–6 months confirm non-union. **Clinical Pearl:** Pseudarthrosis (option C) is a *type* of non-union (specifically atrophic non-union with false joint formation), not a separate category at the same hierarchical level as non-union itself. [cite: Rockwood & Green's Fractures in Adults, 8th ed., Ch. 1; Campbell's Operative Orthopaedics, 13th ed.]