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Last Updated: Wednesday, 22 October, 2003, 23:07 GMT 00:07 UK
'Goo measure' could help hip ops
By Caroline Ryan
BBC News Online health staff

Hip replacement image - (copyright http://www.medicalmultimediagroup.com)
The cement is a crucial part of the hip replacement operation
Researchers are developing a device to measure the "gooiness" of the crucial cement used to fix in replacement hip joints.

It is crucial to get the consistency of the cement right because, if it is not, the replacement joint may wear out more quickly.

The new ball and socket is attached to the patient's bones using bone cement, a putty-like substance that penetrates into the pores in the bone and then sets hard, locking the prostheses in place.

The joint has to be strong enough to bear the pressure as someone walks - which can be up to 10 times a person's body weight.

The cement can start to work loose from the bone, causing little bits of debris to float around in the joint, causing infection and making any further operations on the joint very difficult.

The best way to prevent this happening is to fix in the prosthetic joint as firmly as possible - and that means using the right consistency of cement.

The cement is made by mixing a powder and a liquid into a paste, which is then stirred and left to stand for a few minutes.

It has to be runny enough to penetrate tiny pores in the bone, but stiff enough to hold the prosthesis in place while it sets.


Currently, surgeons have to test the cement's viscoelastic, its "gooiness", by taking a pinch and estimating if it is ready to be used.

But this method can be affected by a range of factors, such as the temperature in the theatre or if it has been stored in a cool room.

A simplified image of the hip device
The aim is to take the guesswork away
Dr Ben Hanson, University of Leeds
Scientists do have a device called a rheometer which they use to measure "gooiness" - but it costs thousand of pounds and is very delicate and difficult to sterilise, making it unsuitable for use in an operating theatre.

The researchers, from the school of biomechanical engineering at Leeds University, designed a small, cheap, disposable device which can accurately measure the cement's consistency because scientists know how the cement behaves and how the device reacts to it.

Computer readings based on these measurements tell surgeons when the cement is ready to be used.

Researchers say it could be around five years before the device is ready to be used in operations.

Dr Ben Hanson, a research fellow who worked on the device, told BBC News Online: "The long-term success of hip replacements really depends on the quality of the fixation between the prosthesis and the bone.

"At the moment, it's largely dependent on the experience and estimation of the surgeon who has to decide when the best time to put the cement in, and what the best consistency is.

"The aim is to be able to quantify this and to take the guesswork away."

Part of the puzzle

Mr Keith Tucker, Honorary Secretary of the British Hip Society, told BBC News Online: "An important factor in hip replacements is the consistency of the cement.

"It would be very good to know that we can control it better."

But he added: "This is just one part of the puzzle. There are so many other variables with hip replacements."

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