The purpose of this paper is to report the use of total knee arthroplasty, a megaprosthesis, as a treatment in elderly patients who have a persistent nonunion of a supracondylar femur fracture. This case report includes two elderly patients who sustained supracondylar femur fractures that failed to unite with standard operative fixation methods. Despite multiple procedures during a long period, patients had a persistent nonunion. Both patients underwent total arthroplasty with a cemented kinematic rotating hinge and had significant clinical improvement. The Hospital for Special Surgery (HSS) knee scores increased from fifty-four points to seventy points in one patient and forty-two points to seventy-three points after surgery in the other patient. Both patients had excellent range of motion after surgery. A cemented megaprosthesis appears to be a viable treatment option for persistent nonunions of supracondylar femur fractures in elderly patients. It is well tolerated and permits early ambulation and return to activities of daily living.