Sensor Technology Ltd. - PRODUCT NEWS
Piezo technology helps access artificial joints.
A medical researcher is using an industrial torque sensor to analyse
the performance of implanted eplacement knee joints, hoping to increase
the understanding of their long term post-surgery performance.
The programme is being run by Judith Lane, between now and the end of 2007 at Queen Margaret University College in Edinburgh. 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 beginning this latest research Lane had to design, build and validate a rig that could assess the performance of patients' artificial joints. Explaining the reasons for the project, she said: "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."
The rig developed for the project centred on a 100Nm Torqsense transducer from Sensor Technology, with an extended through shaft supporting crank arms on both ends.
"We very carefully align the axis of the transducer 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. This means that we have isolated the joint and can run through a series of tests with the transducer constantly monitoring torque so that we can build up a profile of the knee's performance."
Non-contact sensing head
The sensing head of the Torqsense transducer does not contact the shaft under test, so exerts no back torque that has 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.
"By using the Torqsense transducer, we can calculate the resistance to movement created by soft tissues around the knee, at any point in range," said Lane.
For each patient several readings are taken 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 ability of the knee to undertake common 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."
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