The 3rd International Symposium on Engineering, Energy and Environment edition:3 location:Bangkok, Thailand date:17-20 November 2013
A large number of total knee arthroplasties are performed every year, during which the knee joint is replaced by an artificial implant. Although literature shows high survival rates, the number of revisions is high, due to the large number of primary TKR’s: approximately 5 to 10% of the prostheses need to be replaced within 10 to 15 years. Loosening of a component is a main indication for revision, but the preoperative diagnosis is a difficult one. The existing methods to detect loosening, like radiography, are not sensitive and reliable enough.
Modal analysis has been successfully applied in biomechanics to assess the initial stability of a femoral implant, and to assess the stability of dental implants. However, the assessment of the stability of cemented knee implants by vibration analysis is a domain less explored yet. This preliminary in vitro study aims to explore the sensitivity of vibrational techniques in detecting loosening of tibial implants. The influence of fixation between implant and artificial bone on vibration responses was investigated by means of modal analysis. In addition, a finite element model (FEM) was created to represent the artificial bone used in the experiments. This FEM model was then refined by correlating the computational model with in vitro test results. In the experiments, four GENESIS II tibial implants (SZ4 RT – Smith & Nephew) were inserted in artificial Medium Right Osteoporotic Tibiae (1117-130 - Sawbones) with different fixations. The tibiae were suspended on a stiff metal frame by soft bungees, excited by a hammer blow or shaker excitation, and modal parameters and frequency response functions were obtained.
Results showed that the fixation of the implant influences the resonance frequencies of the bone-implant structure. In general, a better fixation increases the resonance frequencies and more complicated modes are more sensitive. A FEM was obtained suited for further study. The FEM can be used to simulate different loosening situations and to find the most sensitive vibrational modes.