A medical researcher is using an industrial torque sensor from Sensor Technology to analyse the performance of implanted replacement knee joints, with the aim of increasing the understanding of their long-term post-surgery performance.
Judith Lane is running programme throughout 2007 at Queen Margaret University College, Edinburgh, to investigate the performance of implanted knee joints. As well as this research, which should lead to the awarding of a PhD, she holds a Masters degree in bioengineering, is a qualified physiotherapist, and lectures at both undergraduate and postgraduate level in the School of Health Sciences.
Before she could begin her latest research project she had to design, build and validate a rig that could assess the performance of patients' artificial joints.
Relationship between function and stiffness
Lane explains the need for the research as follows: "Most replacement knee joint surgery is extremely successful, but a few patients do not achieve the function we would expect. By exploring the relationship between function and stiffness, this research hopes to reveal if stiffness in the joint is the reason why."
To do this she has developed a rig centred on a 100Nm TorqSense transducer from Sensor Technology, with an extended through-shaft that supports crank arms on both ends.
"We very carefully align the axis of the TorqSense with the patient's knee and attach the ankle to the end of one crank. We can then use the other crank to move the knee without the patient having to put in any muscular effort, thus we have isolated the joint and can run through a series of tests with the TorqSense constantly monitoring torque so that we that build up a profile of the knee's performance."
Non-contact torque measurement
Sensor Technology says that the TorqSense sensor is unique in that the sensing head does not contact the shaft under test, so it exerts no back-torque that would have to be accounted for in calculations. Instead two piezo-ceramic combs, designed to deform microscopically as torque in the shaft changes, are glued to the shaft and monitored over a radio wave connection. Because the combs are based on piezo technology, they can be supplied with sufficient operating power via the radio signals. Their electro-resistive characteristics vary with the deformation, changing the output radio signal proportionally to the torque in the shaft.
Lane says: "By using the TorqSense transducer, we can calculate the resistance to movement created by soft tissues around the knee, at any point in range."
For each patient, Lane will take several readings to develop a picture of the dynamics of the knee joint. This data will then be correlated with the findings from a battery of tests to establish the joint's ability to undertake common daily activities such as climbing stairs, sitting down and getting into the bath.
"By cross-referencing the two sets of data we should be able to build up an exact profile of the joint's performance, and assist decision-making between the patient, physiotherapist and orthopaedic surgeon relating to future treatment."
To order a copy of the TorqSense brochure, go to this page.
