Case: The case reported involves a patient who developed an unexplained decrease in hemoglobin after acetabular fracture surgery in the prone position. Repeat abdominal computed tomography was remarkable for a massive subcapsular spleen hematoma secondary to rib fracture impingement, which required splenectomy. Conclusion: The spleen can be injured by a fracture rib during prone positioning for fixation of an acetabular fracture. Prone surgical positioning may cause iatrogenic intra-abdominal organ injury in patients with displaced lower rib fractures. Lateral positioning should be considered for acetabular surgery in patients with rib fractures.