Intra-operative monitoring of orthopaedic implant stability by vibration analysis

The success rate of orthopaedic implants is strongly dependent on the initial fixation, but the objective intra-operative assessment of primary stability of cementless implants is still a challenge and, moreover, excessive press-fitting of the implant can cause intraoperative fractures. In a series of in vitro and in vivo experiments the change in the frequency response function (FRF) of the hip stem/femur structure during implant insertion was studied and, to better understand the influence of changing contact conditions on the resonance frequencies a finite element analysis was set up. Especially in the range of higher frequencies, the FRF change provides reliable information regarding the stability evolution of the implant-bone system during the insertion. The protocol described in this paper can be used to accurately detect the insertion end point and to reduce the risk for intra-operative fracture in total hip arthroplasty. The vibrational method based on FRF analysis can be adapted and extended to other kinds of orthopaedic implants.