An 18-year-old patient with a tibia/fibula fracture develops increasing pain 12 hours after injury despite adequate analgesia. The most likely diagnosis is?

• A. Avascular necrosis
• B. Myositis ossificans
• C. Compartment syndrome
• D. Reflex sympathetic dystrophy

Answer: (C)

Pain out of proportion to exam after a fracture, especially with increasing pain despite analgesia within hours, points to compartment syndrome. When a limb is confined in a tight fascia, swelling from the injury raises the pressure inside the compartment. This rising pressure compresses blood vessels, lowers tissue perfusion, and causes ischemic pain that often feels disproportionate and may worsen with passive stretching of the muscles in that compartment. It’s an emergency because ongoing ischemia can lead to muscle necrosis, nerve injury, and lasting disability if not treated promptly. In this scenario, the clock is critical, and urgent assessment is needed—either by measuring the intracompartmental pressures or proceeding with fasciotomy if suspicion is high.

Other diagnoses don’t fit this acute pattern: avascular necrosis typically presents later after a vascular injury to the bone; myositis ossificans develops weeks after injury with heterotopic bone formation around soft tissues; reflex sympathetic dystrophy (complex regional pain syndrome) emerges weeks to months later with disproportionate pain and autonomic signs.