An implantable electronic system for in vivo stability evaluation of prostheses in total hip and knee arthroplasty

摘要

Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are relatively new biomedical techniques developed during the last century, which are frequently recommended for patients with joint diseases. In spite of their success and huge popularity, the postoperative failure rates for these procedures remain significant. Migration and micromotion of the implant are the primary indicators of its postoperative stability and many in vitro measurement techniques have been discussed. However, effective, practical methods to measure these metrics in vivo have proven elusive and the evolution of such a technique is the subject of this thesis. An implantable, remotely interrogated electronic system for the in vivo measurement of both micromotion and migration in the axial direction is proposed. The main purpose of the device is to improve the ability of clinicians to assess the longterm stability of orthopaedic implants and also to plan and optimise patients’ rehabilitation protocols. The system is based on a modified form of differential variable reluctance transducer (DVRT) in which the nullpoint of the system set automatically by means of a selfcalibration process. Simulations and preliminary in vitro measurements on the bench show that the selfcalibration algorithm works correctly in spite of component tolerances and initial set up errors, allowing a gross displacement (migration) to be measured with a resolution of 15 �m and a range from 0 to 4 mm, and that the device can measure micromotion with an amplitude as low as 1 �m in the range from 200 �m to 200 �m. Accuracy of less than 10 % are achieved in both micromotion and migration measurements. Prototypes of all the major components and subsystems have been fabricated in CMOS integrated circuit (IC) technology as part of the project. Measurements support the feasibility of constructing an integrated version of the complete system for implantation and in vivo use in the future.