An implantable electronic system for in-vivo stability evaluation of prosthesis in Total Hip and Knee Arthroplasty

This paper describes an implantable system for the in vivo measurement of both micromotion and migration in applications such as total hip arthroplasty (THA) and total knee arthroplasty (TKA). The system is based on a modified form of linear variable differential transformer (LVDT) whose null-point is set automatically by means of a self-calibration algorithm. The self-calibration process not only allows the measuring bridge to work at maximum accuracy (i.e. for micromotion measurements) but also automatically records gross changes in position (migration). Simulations and preliminary measurements show that the calibration algorithm works correctly in spite of component tolerances and initial set up errors and that the device can measure micromotion with an amplitude as low as 1 μm with a gross displacement (migration) in the range 0~±4 mm.