Nerve Damage, Broken Humerus With Minimal Function After Accident, Fever, Had CT Scan, Blood Culture And Urine Culture. Cause For Fever?

Hi, my 17 year old son was in a head on car accident Monday ad has been in the hospital since. He has a broken humorous and has minimal function in it( was told possible nerve damage), two large gashes on his head, a mild concussion , large cut on his left thumb( tendons where exposed and function isn t the same ) since yesterday he developed a high fever , it reached 105 and saint go below 104 for over 10 hours and he has been on antibiotics since he was admitted. He still Has a fever that doesn t go below 102. They did a CT scan , blood cultures and urine cultures, checked all the exposed areas and found no infections. What could be causing the fever? I m very concerned.