Instrumented Knee Prosthesis for Force and Kinematics Measurements

In this work, we present the general concept of an instrumented smart knee prosthesis for in-vivo measurement of forces and kinematics. This system can be used for early monitoring of the patient after implantation and prevent possible damage to the prosthesis. The diagnosis of defects can be done by detecting the load imbalance or abnormal forces and kinematics of the prosthetic knee in function. This work is a step towards the fabrication of an instrumented system for monitoring the function of the knee in daily conditions. Studying the constraints of commercially available prostheses, we designed a minimal sensory system and required electronics to be placed in the polyethylene part of prostheses. Three magnetic sensors and a permanent magnet were chosen and configured to measure the prosthetic knee kinematics. Strain gauges were designed to measure the forces applied to the polyethylene insert. Kinematic and force measurements were validated on a mechanical knee simulator by comparing them to different reference systems. Embedded electronics, including the A/D converters and amplifier were designed to acquire and condition the measurements to wirelessly transmit them to an external unit. By considering the necessary power budget for all components, the optimum coil for remote powering was investigated. The necessary rectifier and voltage doubler for remote powering were also designed. This is the first system capable of internally measuring force and kinematics simultaneously. We propose to package the system in the polyethylene part, bringing versatility to the instrumented system developed, as the polyethylene part can be easily modified for different types of prostheses based on the same principle, without changing the prosthesis design.

Instrumented Prosthesis for Knee Implants Monitoring

Shafqat Ali, Kamiar Aminian, Arash Arami, Oguz Atasoy, Arnaud Bertsch, Catherine Dehollain, Hooman Dejnabadi, Pierre-André Farine, Willyan Hasenkamp Carreira, Brigitte Jolles-Haeberli, Eric Meurville, Philippe Renaud, Peter Ryser, Matteo Simoncini, Steve Tanner

In this work we present an instrumented smart knee prosthesis for in-vivo measurement of forces and kinematics. Studying the constraints, we designed minimal sensory systems to be placed in the polyethylene part of the prosthesis. The magnetic sensors and a permanent magnet are chosen and configured to measure the relative kinematics of the prosthesis. Moreover, the strain gauges were designed to measure the forces on the polyethylene part. The kinematic and kinetic measurements on a mechanical knee simulator are validated toward reference systems. The supplementary electronics, including the A/D, amplifier, rectifier and voltage doubler are designed. Consequently, by considering the necessary power budget for all the components to be performed, the optimal coils for remote powering is investigated. The system will be packaged in the polyethylene part. Therefore, by the end we will have a smart polyethylene part which can be easily modified for different types of the knee prosthesis without changing the prosthesis design.

IEEE2011

Accurate Measurement of Concurrent Flexion-Extension and Internal-External Rotations in Smart Knee Prostheses

Kamiar Aminian, Arash Arami, Axelle Vallet

In this work, we present a magnetic measurement system for integration into smart knee prostheses to accurately measure the combination of two knee rotations; namely Flexion- Extension and Internal-External rotations. This measurement system consists of two permanent magnets inserted into the femoral and tibial parts of the prosthesis and a configuration of anisotropic magneto-resistive sensors placed in its polyethylene part. The sensor configuration was designed according to the sensitivity analysis. Several angle estimators were defined to obtain accurate angle estimations. These estimators ranged from different linear regression models to artificial neural networks. The estimators were trained and tested on several dynamic measurements of rotations of the prosthesis parts in a mechanical knee simulator also monitored using a stereophotogrammetry motion capture system. Considering the best estimators, the errors (mean±SD) were 0.0°±0.9° and 0.2°±1.1° for IE and FE angle estimations respectively. The imposed Abduction- Adduction (AA) rotations effect was investigated on the estimators in two cases: when the estimators were trained on data without AA (Case 1) and with AA (Case 2). The Internal- External angle estimators showed high robustness to the imposed AA. The recorded errors for the best Flexion-Extension estimator were 0.9°±2.7° for Case 1 and 0.3°±1.7° for Case 2. The proposed system has thus demonstrated its ability to accurately estimate concurrent Flexion-Extension and Internal-External rotations.

Institute of Electrical and Electronics Engineers2013

A new method for unconstrained measurement of knee joint angle and timing in alpine skiing : Comparison of crossover and crossunder turns

Kamiar Aminian, Julien Chardonnens, Julien Favre

Timing is an important part in the analysis of alpine skiing technique. Key events extracted from dynamics and kinematics of ski were previously proposed, but timing of body segments kinematics is also required to understand the biomechanics and to assess the performance. In this study, we proposed a new method based on inertial sensors to measure timing parameters based on body segments kinematics. To show the efficacy of the method, angle and timing of knee joints during crossover and crossunder techniques were compared. Significant differences were obtained for the timing, but not for the amplitude of the knee angles. The proposed system reported a good repeatability, did not encumber the athletes and allowed the measurement of body movement during the whole run. So it could easily be used to assess performance in training conditions.

2010