A 35-year-old construction worker sustains a crush injury to his forearm. He is diagnosed with acute compartment syndrome. Which is the most common compartment affected in upper limb compartment syndrome?

Explanation

## Most Common Compartment in Upper Limb Compartment Syndrome **Key Point:** The volar (flexor) compartment of the forearm is the most commonly affected compartment in upper limb compartment syndrome, accounting for >70% of cases. ### Anatomical Considerations The volar compartment contains: - **Superficial layer:** Pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris - **Intermediate layer:** Flexor digitorum superficialis - **Deep layer:** Flexor digitorum profundus, flexor pollicis longus, pronator quadratus - **Neurovascular:** Median and ulnar nerves, radial and ulnar arteries ### Why Volar Compartment is Most Vulnerable | Feature | Volar Compartment | Dorsal Compartment | |---------|-------------------|--------------------| | Muscle mass | Large (9 muscles) | Smaller (11 muscles, but less bulk) | | Fascial rigidity | High | Moderate | | Injury frequency | Common (crush, fractures) | Less common | | Prevalence in compartment syndrome | 70–80% | 20–30% | | Functional consequence if missed | Volkmann's contracture | Claw hand deformity | **Clinical Pearl:** Volar compartment syndrome presents with the classic **"5 Ps"**: Pain (especially with passive finger extension), Pressure (tense compartment), Paresthesia (median/ulnar nerve), Pallor, and Pulselessness (late sign). Pain with passive extension of fingers is the earliest and most sensitive sign. **High-Yield:** Volkmann's contracture is the devastating late sequela of missed or inadequately treated volar compartment syndrome—irreversible flexion contracture of the forearm and hand due to ischemic muscle necrosis. ### Mechanism of Injury Volar compartment syndrome in the forearm commonly follows: 1. Crush injuries to the forearm 2. Supracondylar fractures of the humerus (most common cause in children) 3. Fractures of radius and ulna 4. Tight casts or dressings 5. Reperfusion injury after vascular repair **Mnemonic: CRUSH** — Common causes of forearm compartment syndrome: - **C**rush injuries - **R**eperfusion (post-vascular repair) - **U**pper limb fractures (supracondylar, radius/ulna) - **S**welling (burns, tight casts) - **H**emorrhage (vascular injury)