Guided wave analysis of osseointegration at bone-prosthesis interfaces

Advances in medicine have led to the development of prostheses that can be integrated directly to the host bone of residual limbs. Osseointegration of the prosthesis comes with many benefits including its use in patients with short residual limbs. There are also a number of challenges associated with their use including high rates of tissue infection, bone fracture, and uncertainty in determining when the limb can be loaded after surgery. This paper explores a practical sensing approach to monitor the healing process of osseointegrated prostheses using instrumentation attached to the percutaneous tip of the prosthesis. Specifically, guided wave methods are used to characterize the degree of bone growth and bone integration at the prosthesis interface. Prosthetic models consisting of titanium femoral stems implanted in artificial synthetic bones are employed to simulate the bone-prosthesis interface. Piezoelectric transducers are mounted to the percutaneous end of the prosthesis to introduce controlled body waves. The prosthesis acts as a wave guide allowing the guided waves to interrogate the bone-prosthesis interface inside the limb. Due to the constraints imposed by the prosthesis boundary conditions, three guided wave types are introduced including longitudinal, torsional and flexural waves. Tone burst signals were applied to a piezoelectric lead zirconate titanate (PZT) actuator array mounted to the rod to generate longitudinal waves in the prosthesis. Waves reflected in the prosthesis are received by the PZT array and analyzed to correlate changes in wave properties with implantation depth. Both numerical simulation and experimental testing are conducted to validate the use of reflected wave energy as a wave feature sensitive to penetration depth.