Design of an intramedullary leg lengthening device with a shape memory actuator

The procedure and the external fixator for lengthening long bones was developed by G.A. Ilizarov in the late 1960's. This technique has, despite its proven abilities for leg lengthening and correction of angular deformities, some considerable disadvantages for the patients. Discomfort, infections and restricted weight bearing are some reasons for the development of a completely intramedullary device for leg lengthening. The device developed at the Laboratory of Biomechanical Engineering, University of Twente, is a telescopic intramedullary nail with a maximum diameter of 13 mm, which can be lengthened with 0.5 mm steps induced by a shape memory alloy actuator. The electrical energy for the actuator is supplied from outside the body by inductive coupling of two solenoid coils. Internally, the electrical energy is transformed to thermal energy by Thermofoils and Peltier-elements.