Regeneration of upper femur after subperiosteal resection

A 16-year-old patient had total thigh fillet for decubitus ulcer with an infected hip joint. The patient had extraosseous calcification and infection and was hospitalized again one year later for operation. Approximately four years after the initial operation the patient regenerated a femoral head, neck, and approximately 20 cm of the femoral shaft. This was resected. How often does this occur and should we take steps to obliterate the periosteum when doing a subperiosteal thigh fillet procedure?