Acoustic emission technology can warn of impending iatrogenic femur fracture during femoral canal preparation for uncemented hip replacement. A cadaveric animal bone study

During uncemented hip arthroplasty the femoral prosthesis can be fitted too tightly into the femoral canal, causing a hoop-stress fracture of the proximal femur. The research undertaken evaluated Acoustic Emission (AE) technology as a potential method of detecting a fracture forming in this manner, in an attempt to assess whether this technology may be used as a means of early warning of impending fracture during surgery. Deer femora were prepared in a manner similar to surgery and uncemented hip arthroplasty broaches were inserted until fracture occurred. AE sensors were mounted on the femoral cortex and also on the broach. Five femora were fractured manually by hammering the broaches in a manner similar to surgery. Four femora were fractured using a hydraulic loading machine to insert the broach. Stepwise increases in the AE signals coincided with stepwise increases in surface strain of the femoral cortex, crack mouth growth and fracture. Both sensors recorded similar signal profiles. The sensor on the femur registered greater magnitude signals than the sensor on the broach, suggesting that there is signal impedance across the bone-broach interface. AE signals from sensors mounted on the femur and on the broach can detect damage processes happening within the femur during insertion of the broach in the time period of approximately 100 s prior to fracture. These damage processes may represent micro cracking, and ultimately fracture. This supports the possibility of the use of AE signals as a means to monitor internal damage within the femur and possibly predict impending fracture. It is clear that AE signals change significantly prior to fracture however in order to attempt to develop a warning system, further understanding of the significance of the signals and limitations of these methods must be gained