Accurate internal–external rotation measurement in total knee prostheses: A magnetic solution

Reference-Free Automated Magnetic Sensor Calibration for Angle Estimation in Smart Knee Prostheses

“…The minimally-designed system consisted of a permanent magnet placed in TP and an AMR sensor located on the axis of rotation of PE (Fig. 2) [24]. As long as the magnet and sensor are in the same plane pointing to each other and their relative angle is small, the measurement equations can be considered as sinusoidal equations (1) and (2) [24], where a 1 , a 2 and k 1 , k 2 are gains and offset of the models.…”

“…To validate the reference-free calibration method and evaluate the performance of the resultant IE angle estimators, we compared the result to the reference kinematics measured by a stereophotogrammetry motion capture system, and to the reference-dependent trained IE estimators proposed earlier [24]. The instrumented knee prosthesis was fixed in a manually-operated knee simulator able to perform different rotations.…”

“…In one of the recent studies, a configuration of anisotropic magnetoresistive (AMR) sensors and a permanent magnet, integrated into the knee prosthesis, was used to estimate the knee internal-external (IE) rotation [24]. The AMR sensors were chosen due to their high resolution [25], and their success in measuring the 3D orientation and position of a magnet [26] in different biomedical applications such as gastrointestinal motility studies [27], and step detection during walking [28].…”

An Analog Front-End and ADC Integrated Circuit for Implantable Force and Orientation Measurements in Joint Prosthesis

“…In the present case, six channels were selected to be a good compromise between accuracy and hardware complexity. Experimental measurements were carried out with a knee simulator and six AMR sensors to validate the accuracy of the proposed orientation sensing principle [3]. A difference of 0.6° RMS was obtained in the dynamic angle estimation compared with an external optical measurement with vicon cameras (Fig.…”

“…Finally, the kinematics measurement of the prosthesis from the inside of the body is a challenge; while forces can be measured using strain gauges positioned on the joint interface, and vibrations are detected with accelerometers, the prosthesis kinematics cannot be sensed with traditional methods, due to the impossibility of electrical or optical communication between the two joint parts of the implant. A solution is to use a local magnetic field generated by a permanent magnet located in one part of the prosthesis, and to measure its field intensity by multiple magnetic sensors located in the other part and sensitive to different directions [3]. The 3D relative orientation of the two prosthesis parts can then be computed by merging the different sensor signals.…”