Objective: Background: Case Report: Conclusions: Unusual clinical course Lower-extremity compartment syndrome (CS) is a rare yet devastating complication of posterior spinal fusion. We present our case to discuss this occurrence and possible risk factors. An obese 15-year-old boy with adolescent idiopathic scoliosis underwent posterior spinal instrumentation and fusion, which was complicated by loss of 5000 mL of blood. He received 11 946 mL of intraoperative infusions to maintain adequate perfusion. Throughout the procedure, his sensory and motor evoked potentials (EPs) were normal. On postoperative Day 1, the patient complained of mild anterior and lateral left leg pain, which became severe by Day 2. Physical examination revealed tense anterior and lateral compartments. He immediately underwent a fasciotomy with irrigation and debridement. On follow-up, the patient has regained full ankle range of motion and has 5/5 dorsiflexion and plantar flexion. He has a weak extensor hallucis longus (1/5) but has been able to fully participate in sports. CS should be suspected when a patient has significant postoperative pain in areas remote from the spine. Risk factors such as excessive blood loss, large volumes of infusion, obesity, prolonged operative time, and EPs can be contributory.