Natural frequency analysis of osseointegration for trans-femoral implant.

Osseointegration trans-femoral implants are a new orthopaedic anchoring method to attach prosthetic limbs. The clinical success of this promising technique depends on the effectiveness of osseointegration achieved after implantation. The aim of this study is to use the resonant characteristics of the implant system to determine the changes in stability as a reflection of boundary condition of the implant. With a small mechanical excitation, Vibration responses of the trans-femoral implant to a small mechanical excitation were measured using an accelerometer and the vibration signal was analyzed using Fast Fourier Transform (FFT) software to obtain the fundamental natural frequency (NF) of the implant system. In-vitro study was conducted using different silicone rubbers to simulate the interface condition. The result showed that a high NF corresponded to a high elastic modulus of the interface material between the implant and bone. A preliminary in-vivo study with one osseointegration trans-femoral implant patient showed that there was a decrease of NF after initial weight bearing rehabilitation. After continued weight bearing, the NF gradually returned to the pre-loading level at around day 24 and the general trend of the NF reached a stable state 38 days after the first weight bearing exercise.