"Shape Memory Driven Intramedullary Nail for Bone Elongation"

The authors present a newly developed intramedullary implant for bone elongation and bone segment transport that is driven by a shape memory element. During surgical treatment, the intramedullary nail serves to stabilize and enables the body's own formation of new bone material for limb lengthening or bridging of defects according to the “Betz Baumgart method”. After dissection of the tubular bone, the medullary nail is inserted into the medullary cavity and fixed. A subcutaneous receiver coil obtains the command twice a day to activate the thermal effect of the shape memory element by means of high-frequency energy transport. Therefore the fracture gap increases twice by 0.5 mm each. This leads to the stimulation of osteocyte formation and the desired bone length. With this intelligent intramedullary nail it will be possible to lengthen bones more gently as hitherto and to monitor, document and evaluate continuously the whole elongation process for the first time.

Recently, three such nail prototypes were tested in a cadaver trial on a human corpse in a German clinic. At present a re-design of this shape memory driven implant is taking place with one focus on a novel coil geometry and control technology on the one hand and another focus on the novel connection technology for the drive components on the other hand. In particular, the approach to a reliable connection technology that withstands high tensile forces between the active shape memory element and the implant parts in a small installation space will be described.