Mechanical Design and Prototyping Considerations for an Intramedullary Nail for Extending Bone Sections

An orthopedic distractor device is currently being developed for extending bones or bridging a gap in a bone. The device is designed to fit into the medullary canal of a human femur or tibia. By virtue of telescopic motion between two mating parts, the device can extend axially inside a dissected bone, elongate it to desired length. The distractor is actuated by means of a miniature electrical drive system, which is energized and controlled from outside of the body without any direct physical connection or cabling. In this study mechanical design and prototype manufacturing considerations of the intramedullary distractor device are discussed. An important limitation in design of this device is the availability of a suitable drive system that will fit into the intramedullary space of the bone, which has a diameter of less then 12 mm. The nail must withstand axial forces with a magnitude of 2000 N, which is exerted by extending the muscles, especially during the late stages of the distraction operation. Since the designed device is intended to be used inside the human body, proper insulation from the surrounding body fluids must be provided, thus sealing is also an important design consideration. A preliminary design is presented that will achieve the desired requirements.