A Novel Inductive Biphasic Proximal Humerus Internal Fracture Fixator

There are about 14.5 occurrences of fracture fixation per every 100, 000 in the population every year. As a result, approximately 370, 000 hospitals visits occur every year. Presently, there are two exclusive schools of thought for internal fracture fixation: rigid and biological fixation. Rigid fixation utilizes stiffer implants for precise fragment positioning. However, significant stress shielding occurs as a result of the fixation. Biological fixation utilizes more flexible implants to reduce surgical trauma and allows for more functional healing but the possibility of non-union and delayed healing increases as well. We aim to combine these previously exclusive schools of thought by developing a novel proof-of-concept biphasic internal fixator design which varies its stiffness between the typical stiffness of the two schools. The design utilizes a shape memory polymer (SMP) to allow for biphasic actuation of the device. Upon inductively heating the polymer above its glass transition temperature (Tg), the SMP layer changes from a thicker initial shape to a preprogrammed "memorized" thinner shape. This leads to change of cross-sectional area and moment of inertia of the device resulting in a decreased axial, torsional, and bending stiffnesses; thus, reducing the effects of stress shielding while ensuring precise fragment union. ANSYS was used to perform finite element analysis (FEA) on our model of the device. Preliminary results from our FEA suggest that a forty percent reduction in stiffness may be achieved through utilizing a material which decreases its thickness from 7 mm to 2 mm.