A dynamic intramedullary implant for bone fracture repair

Intramedullary (IM) nails are commonly used in the fixation of long bone fractures such as fractures of the femur and tibia. They are commonly hollow, rigid rods made from 316L steel or titanium alloys. Static locked IM nails which ensure that both ends of the long bone do not move relative to each other have traditionally been used, however, recent research suggests that such rigid bone-nail constructs do not provide optimal conditions for bone healing. Dynamic fixation allows the bone fragments to move a prescribed distance relative to each other, thus causing micro-motions at the fracture site and stimulating healing via callus formation. This paper describes the development and proof of concept of a new dynamic IM nail, incorporating an internal mechanism which allows for a tailored micro-motion at the fracture site. In vitro bench testing using synthetic composite bones (Sawbones, USA) was carried out to compare the performance of the new device with standard IM nails under compression, four-point bending and torsional loads. It was found that the dynamic implant performed well in comparison the standard nail and provided the required micro motion at the fracture site.