We encountered a case in which improving limited knee flexion was difficult after surgery for a femoral shaft fracture. A woman in her 20s sustained polytrauma including a femoral shaft fracture. Anterograde intramedullary nailing of the femur was performed at another hospital on the day after the injury, and 75 days later she was transferred to our hospital for rehabilitation. The referral document indicated the fracture was an AO type C2 fracture, and postoperative plain radiographs showed that one of the locking screws in the distal femur was inserted from the anterior to posterior side. She was discharged to home at 90 days post-injury, but knee joint flexion was still limited to 95°, and she complained of pain in the final flexion range where a side-stop screw was inserted at the front of the knee. Imaging and physical findings indicated that knee flexion was restricted by contracture of the suprapatellar supporting tissues, so an approach focusing on these tissues was added to her outpatient exercise regimen. As a result, knee flexion was improved to 150° at 140 days post-injury and she had no interference in activities of daily living.