Closed intramedullary nailing is a classical therapeutic approach for floating knee injuries. An appropriate positioning is critical for a successful surgery. However, there is a lack of an ideal auxiliary device to facilitate the implantation of intramedullary nail. The authors developed a simple lower limb outrigger frame (SLLOF), which is made of nylon, to facilitate the nail implantation process. The SLLOF could be radiolucent and autoclavable. A total of 31 patients with floating knee injury underwent the closed intramedullary nailing assisted by SLLOF. The average operative duration was 91.0min, and all tibial and femur fractures reached bony union. The SLLOF could assist well insertion of intramedullary nail for the treatment of floating knee injuries, with the advantages of simple operation, less manpower, easy imaging access but less radiation exposure, and more cost-effectiveness.