A 25-year-old white man with a medical history significant only for polysubstance abuse presented to the emergency department with concerns of weakness and numbness of the right lower leg on awakening. His examination was remarkable for profound weakness of ankle dorsiflexion and plantar flexion, absent ankle jerk, and hypesthesia of the right lower leg, especially laterally to his shin. He had marked tenderness of the lower back at approximately L3 but no other obvious physical findings. His white blood cell count was elevated at 206 000/μL (to convert to ×109/L, multiply by 0.001), and later, his creatine kinase level was noted to be 18 860 U/L (to convert to microkatals per liter, multiply by 0.0167). An emergent magnetic resonance image of the lumbosacral spine was normal. A pelvic computed tomographic scan showed a mass that, after correlation with the magnetic resonance imaging study (Figure 1 and Figure 2), was diagnosed as muscle edema of the pelvic muscles. After the patient was asked once more whether he had had a trauma (which he denied initially, likely because he was on probation), he admitted to an altercation that resulted in someone knocking him over and sitting on him for a prolonged period and that he had been falling asleep with his right pelvis on a concrete floor. Obvious muscle edema and pelvic pain developed during his hospitalization, but his sciatic mononeuropathy improved with conservative management, and 5 days after presentation, his ankle plantar flexion was graded 4 of 5 and dorsiflexion, 2 of 5, and hypesthesia was restricted to a superficial peroneal nerve pattern.