An 18-year-old patient sustains a tibia/fibula fracture and 12 hours later has increasing pain despite analgesics. Which of the following is the most likely diagnosis?

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

Answer: (A)

Compartment syndrome is the emergency situation here: after a tibia/fibula fracture, rising pressure within a closed leg compartment impairs perfusion and causes pain that worsens despite analgesia. The key clue is pain that is out of proportion to exam and often intensifies with passive stretching of the involved muscles, occurring within hours of injury. If not relieved, the high intracompartmental pressure can lead to muscle necrosis, nerve injury, and potential limb loss, so urgent decompression is necessary.

Avascular necrosis would not present this acutely; it relates to ischemia of bone tissue and typically develops over longer periods with symptoms tied to specific joints. Myositis ossificans develops weeks to months after injury as heterotopic bone forms in muscle, not within 12 hours. Reflex sympathetic dystrophy (CRPS) presents with ongoing pain and autonomic changes weeks after injury, not as an immediate post-injury complication.