A 40-year-old construction worker is pulled from the rubble after a building collapses and pins his right lower leg. X-rays in the emergency department reveal a comminuted fracture of the right tibia and fibula. The dorsal pedis and posterior tibial pulses are palpable. The patient complains of severe pain that is accentuated with dorsiflexion of the foot. The calf feels tense. What is the appropriate step?