Femoral Test Bed for Impedance Controlled Surgical Instrumentation

The risk for patients during the standard procedure of revision of cemented artificial hip joints is unsatisfactorily highdue to its high level of invasiveness and limited access to the operative field. To reduce this risk we are developing anImpedance Controlled Surgical Instrumentation (ICOS) system, which aims to establish real-time control during a BoneCement (BC) milling process. For this, the relationship between the thickness of the BC and its frequency-dependentelectrical impedance is used to estimate the residual BC thickness. The aim is to avoid unintended cutting of boneby detecting the passage of the BC/bone boundary layer by the milling head. In a second step, an estimation of theresidual BC thickness will be used to improve process control. As a first step towards demonstrating the feasibility ofour approach, presented here are experimental studies to characterize the BC permittivity and to describe the process indetail. The results show that the permittivity properties of BC are dominated by its polymethyl methacrylate (PMMA)fraction. Thus, PMMA can be used as a substitute for future experiments. Furthermore, a Femoral Test Bed (FTB) wasdesigned. Using this setup we show it is feasible to accurately distinguish between slightly different thicknesses of BC.