A 68-year-old man sustains a displaced intracapsular fracture of the femoral neck (Garden grade III) following a fall. He is medically fit for surgery. At 8 weeks post-operatively after internal fixation with cannulated screws, imaging reveals non-union with sclerosis at the fracture site and no callus formation. Which of the following is the MOST likely contributing factor to this complication?

Explanation

## Analysis of Non-union in Femoral Neck Fracture ### Pathophysiology of Non-union **Key Point:** Non-union in femoral neck fractures is primarily a mechanical problem, not primarily biological. The intracapsular location and precarious blood supply make these fractures vulnerable to non-union, but the SINGLE most important modifiable mechanical factor is reduction quality. ### Why Inadequate Reduction (Varus >20°) is the Answer The femoral neck has a unique biomechanical environment: 1. **Shear stress concentration**: A femoral neck fracture is inherently a shear fracture. Varus angulation >20° increases shear forces across the fracture site exponentially, preventing compression and callus bridging. 2. **Loss of load-sharing**: Proper valgus alignment (15–20° valgus) converts shear into compression, promoting callus formation. Varus deformity reverses this. 3. **Intracapsular blood supply**: The femoral head receives blood primarily from the medial and lateral femoral circumflex arteries. Varus angulation kinks these vessels, further compromising perfusion at the fracture site. 4. **Evidence**: Garden grade III (displaced) with inadequate reduction has non-union rates of 30–50%, whereas properly reduced fractures have union rates >90% even in elderly patients. **Clinical Pearl:** The "Garden reduction index" (measuring varus/valgus on AP and lateral views) is the single strongest predictor of union. Residual varus >20° is an absolute indication for revision surgery. ### Why Infection (Option 1) is Wrong While infection can cause non-union, the clinical presentation would include: - Fever, drainage, elevated inflammatory markers (ESR, CRP) - Radiographic lucency around implants (loosening) - Purulent discharge or sinus tract The stem describes **sclerosis and absence of callus** — the hallmark of mechanical non-union (atrophic), not infected non-union (which is typically hypertrophic or shows osteolysis). Infection is a less common cause of femoral neck non-union than mechanical factors. **Warning:** Do not confuse "sclerosis" with "infection." Sclerosis indicates bone death and resorption at fracture margins (atrophic non-union), typical of mechanical failure. ### Why Premature Weight-bearing (Option 2) is Wrong While early weight-bearing can compromise healing in some fracture types (e.g., stress fractures, some metaphyseal fractures), femoral neck fractures are **intracapsular and non-weight-bearing in nature**: - The fracture is above the intertrochanteric line and does NOT bear direct axial load. - Femoral neck fractures are managed with **protected weight-bearing** (toe-touch or partial weight-bearing) even in the early weeks. - Non-union from weight-bearing is more relevant to femoral shaft or intertrochanteric fractures, where load-sharing is critical. The biomechanical failure here is **shear**, not axial overload. ### Why Excessive Soft Tissue Trauma (Option 3) is Wrong While soft tissue trauma can impair healing in open fractures or severely comminuted injuries, femoral neck fractures are typically managed via: - **Percutaneous cannulated screw fixation** (minimal soft tissue disruption) - Or small open approaches (Smith-Petersen or Watson-Jones) These techniques cause minimal additional trauma. The primary determinant of healing is **fracture reduction quality and blood supply**, not surgical approach morbidity. Excessive soft tissue trauma would be relevant in polytrauma or open fracture scenarios, not in a simple displaced intracapsular fracture. ### Summary Table: Non-union Risk Factors in Femoral Neck Fracture | Factor | Mechanism | Preventability | Frequency | |--------|-----------|-----------------|----------| | **Varus angulation >20°** | Increases shear, kinks vessels | High (surgical technique) | Most common | | Intracapsular location | Precarious blood supply | Low (anatomic) | Inherent | | Delayed presentation (>24 hrs) | Vessel thrombosis | Moderate | Moderate | | Infection | Biofilm, osteolysis | Moderate (sterile technique) | Rare (<2%) | | Age >70 | Reduced osteogenic capacity | Low (patient factor) | Moderate | | Osteoporosis | Poor bone quality | Low (patient factor) | Common | **High-Yield:** In NEET PG, femoral neck non-union questions almost always pivot on **reduction quality**. If a stem mentions "non-union" + "femoral neck" + "8 weeks," think **varus angulation** first. ### Management of Non-union Once non-union is established (as in this case), revision surgery is indicated: 1. **Re-reduction** with correction of varus deformity 2. **Valgus osteotomy** (if varus is severe) 3. **Bone grafting** (cancellous autograft to the fracture site) 4. **Reinforcement** with additional screws or a plate 5. Consider **total hip arthroplasty** if patient is elderly and has significant osteoarthritis **Mnemonic:** **VARUS** = **V**arus angulation causes **A**trophic non-union; **R**eduction quality is **U**ltimate; **S**urgery is solution.