A 28-year-old woman is admitted 6 hours after a fall from a height with a closed fracture of the left femoral shaft. Intramedullary nailing is planned. During the procedure, the surgeon notes difficulty in obtaining anatomical reduction of the comminuted fragments. After successful nail insertion, post-operative X-rays show 12° of varus angulation and 8 mm of shortening. The patient develops fever (38.5°C) and tachycardia (110/min) on post-operative day 2, with no signs of surgical site infection. What is the most likely diagnosis?

Explanation

## Fat Embolism Syndrome (FES) in Femoral Fracture ### Clinical Presentation The patient presents with the classic triad of FES: 1. **Fever** (38.5°C) — hyperthermia from inflammatory cascade 2. **Tachycardia** (110/min) — compensatory response 3. **Timing**: Post-operative day 2 — typical onset is 24–72 hours after long bone fracture or intramedullary manipulation ### Pathophysiology of FES **Key Point:** Fat embolism occurs when bone marrow fat enters the venous circulation during: - Intramedullary nailing (reaming and nail insertion increase intramedullary pressure) - Manipulation of comminuted fractures (disrupts marrow sinusoids) - Prolonged delay between injury and fixation (increased marrow edema) **High-Yield:** The **mechanical theory** (fat globules lodge in pulmonary and cerebral capillaries) combined with the **biochemical theory** (free fatty acids trigger inflammatory cascade) explains the systemic symptoms. ### Diagnostic Criteria for FES **Gurd's Major Criteria (need ≥2):** - Petechial rash (chest, axillae, conjunctiva) - Respiratory symptoms (tachypnoea, dyspnoea, hypoxaemia) - Cerebral symptoms (confusion, restlessness, seizures) - Fever **Minor Criteria:** - Tachycardia - Thrombocytopenia - Elevated ESR - Fat in urine or sputum - Retinal changes (cotton-wool spots, Purtscher flecken) ### Differential Diagnosis Table | Condition | Onset | Key Features | Distinguishing Point | |-----------|-------|-------------|---------------------| | **Fat Embolism** | 24–72 hrs post-op | Fever + tachycardia + respiratory/neuro signs | Petechial rash, hypoxaemia, thrombocytopenia | | **Surgical Site Infection** | 3–7 days | Local signs: erythema, warmth, drainage | Wound signs absent; fever without local findings | | **Compartment Syndrome** | Hours to 1–2 days | Pain out of proportion, pain with passive stretch | Acute limb pain; this patient has systemic symptoms | | **DVT/PE** | 3–7 days | Unilateral leg swelling, pleuritic chest pain | No mention of leg swelling; PE presents with dyspnoea but not petechiae | ### Clinical Pearl **Risk Factors for FES in Femoral Fracture:** - Comminuted fractures (this patient) - Intramedullary nailing (especially reaming) - Delay in fixation >24 hours - Multiple long bone fractures - High-energy trauma ### Mnemonic: FEVER-FES - **F**at embolism - **E**arly (24–72 hours) - **V**enous origin (bone marrow) - **E**mbolises to lungs and brain - **R**ash (petechial), respiratory, restlessness - **F**ixation (intramedullary nailing is a risk) - **E**rythrocyte sedimentation rate elevated - **S**ystemic inflammation ### Management 1. **Supportive care**: Oxygen, fluid management, analgesia 2. **Monitor**: Arterial blood gas, chest X-ray, CBC (thrombocytopenia) 3. **Prophylaxis**: Early mobilisation, compression stockings, anticoagulation (controversial) 4. **Severe cases**: ICU care, mechanical ventilation, ECMO if refractory [cite:Rockwood & Green's Fractures in Adults Ch 1]