Technology could monitor hip replacements for signs of wear
25 June 2012 | By Stephen Harris
A new device could monitor hip replacements for signs of wear, powered only by the movement of the user’s walk.
The technology, designed to fit inside a typical prosthetic hip joint, uses a piezo-electric device that generates up to 3.7V of electricity as the user walks to power a strain gauge and a transmitter.
By using the strain gauge to monitor the distance between the prosthesis and the femur leg bone, doctors will able to tell if the replacement is starting to break down and advise the patient on lifestyle changes or the potential need for another operation.
‘Thirty per cent of hip replacements within six years start to show signs of osteolysis,’ said Brunel University student Luke Kavanagh, who developed the device.
‘As the joint comes loose it starts to work away at the plastic cement and these little particles then travel around the body and can actually start to corrode the rest of the femur and the hip.’
The device contains a ball bearing that rolls back and forth as the user walks along and strikes a substrate covered on one side with piezo-electric material (known as a unimorph) to produce electricity.
Kavanagh said the challenge was adjusting the rigidity of the unimorph so that it bent enough to produce sufficient power but was durable enough to survive this repetitive process.
He added that the device could be customised to adjust its output and durability depending on how active the user was.
‘An older person isn’t going to move with any real vigour, so you could put a much thinner unimorph in and get all the electricity from big deflections,’ Kavanagh said.
‘With a young person who’s going to be running around, you can put a much thicker one in, but because the velocity you’re hitting the unimorphs with is going to be so much greater you’d get the electricity you need either way.’
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