A 58-year-old woman with osteoporosis presents 3 weeks after a fall with a right intertrochanteric hip fracture. She underwent open reduction and internal fixation with a dynamic hip screw. On post-operative day 5, she develops acute onset of severe dyspnea, pleuritic chest pain, and tachycardia (heart rate 115/min). Oxygen saturation is 88% on room air. Chest X-ray shows a wedge-shaped opacity in the right lower lobe. D-dimer is markedly elevated. What is the most likely diagnosis?

Explanation

## Clinical Context and Pathophysiology This patient presents with **acute dyspnea, pleuritic chest pain, tachycardia, hypoxemia (SpO₂ 88%), a wedge-shaped opacity on CXR, and markedly elevated D-dimer** on **post-operative day 5** following hip fracture ORIF. This constellation is classic for **pulmonary embolism (PE) from venous thromboembolism (VTE)**. **Key Point:** Hip fracture and major orthopedic surgery are among the highest-risk conditions for VTE. Without thromboprophylaxis, the incidence of DVT after hip fracture surgery approaches 40–60%, with PE occurring in 1–5% of cases (Harrison's Principles of Internal Medicine, 21st ed.). ## Why Pulmonary Embolism is the Correct Diagnosis - **Wedge-shaped (Hampton's hump) opacity on CXR**: This is the classic radiographic sign of pulmonary infarction due to PE — a pleural-based, wedge-shaped density pointing toward the hilum. - **Markedly elevated D-dimer**: Highly sensitive for PE; while non-specific, in this clinical context it strongly supports thromboembolism. - **Pleuritic chest pain**: Caused by pleural irritation from pulmonary infarction — a hallmark of PE. - **Timing (post-operative day 5)**: PE typically occurs within the first 1–2 weeks post-surgery; day 5 is the peak risk window. - **Risk factors**: Age 58, osteoporosis (suggesting reduced mobility), hip fracture, and major orthopedic surgery — all Virchow's triad components (stasis, hypercoagulability, endothelial injury). ## Distinguishing PE from Fat Embolism Syndrome (FES) | Feature | Pulmonary Embolism | Fat Embolism Syndrome | | --- | --- | --- | | **Timing** | Days to weeks post-surgery | 12–72 hours post-injury (peak 24–48 hrs) | | **CXR** | Hampton's hump (wedge), unilateral | Bilateral "snowstorm" diffuse infiltrates | | **Petechiae** | Absent | Pathognomonic (axillae, conjunctiva) | | **Neurological symptoms** | Uncommon | Common (confusion, delirium) | | **D-dimer** | Markedly elevated | Elevated (non-specific) | | **Thrombocytopenia** | Mild/absent | Marked | | **Pleuritic chest pain** | Classic | Less prominent | **High-Yield:** Fat embolism syndrome (FES) classically presents within **12–72 hours** of injury with the **Gurd triad**: respiratory distress, neurological dysfunction, and **petechial rash**. The absence of petechiae, confusion, or thrombocytopenia in this stem, combined with the timing (day 5), pleuritic pain, and markedly elevated D-dimer, makes PE the far more likely diagnosis. ## Why Other Options Are Incorrect - **B (ARDS from fat embolism)**: FES peaks at 24–72 hours post-injury, not day 5. CXR in FES shows bilateral diffuse infiltrates, not a unilateral wedge. No petechiae or neurological signs are described. - **C (Pneumothorax)**: CXR would show absent lung markings and tracheal deviation, not a wedge-shaped opacity. - **D (Aspiration pneumonia)**: Typically presents with fever, productive cough, and consolidation in dependent lung segments; onset is more insidious. **Clinical Pearl:** In any post-operative orthopedic patient with acute dyspnea, pleuritic chest pain, tachycardia, hypoxemia, Hampton's hump on CXR, and elevated D-dimer — **PE must be the primary diagnosis** until proven otherwise. Confirm with CT pulmonary angiography (CTPA), the gold standard (Harrison's, 21st ed.).