UWE Builds Device to Ease Discomfort for Prosthesis Wearers

For wearers of prosthetic or false limbs, the comfort and effectiveness of the socket fit is crucial. New ways of measuring and solving socket pressure points – using load analysis techniques from the aircraft industry – have been developed by engineering and computing researchers at the University of the West of England.

A team from UWE’’s Faculty of Computing, Engineering and Mathematical Sciences has just been awarded a grant of £52,000 by the charity Remedi to further their research, which could lead to widespread benefits.

“In the UK alone there are over 55,000 amputees, over 70% of whom are elderly people with lower limb amputations,” said Dr Siamak Noroozi, Director of the Computational Mechanics Group who is leading the project team.

“Treatment is costly, but a highly advanced prosthesis has little value if the socket is uncomfortable and ineffective. Over time, the stump can shrink and change in size, and excessive pressure can result in damage to remaining tissue. Our research could provide prosthesis specialists with a method of assessing socket fit that is both visual and accurate and best of all, is non-invasive.”

Researchers have already developed a prototype in which the entire socket forms an optical transducer, able to output signals in response to changes in pressure. The technique is based on methods of detecting stresses in highly complex aerospace structures. A special reflective coating is applied inside the polymer socket housing the stump of a limb. Special lenses sensitive to polarised light are used to view the patient walking and clearly reveal the pressure points as contour lines of different colour.

These visual results can indicate problem areas immediately to a prosthetist. But the device has a second string to its bow – the constantly shifting contour lines of pressure can be integrated with a data acquisition system. UWE computing experts are working on software to link this to an artificial neural network capable of being trained to recognise and interpret the input data. “This means we can capture the value of a contour at any given moment,” Siamak said. “We can then use the software to predict pressure between the residual limb and the socket. This can be stored and analysed, and used to build a database able to predict more accurately how minute changes to the configuration of a socket will affect the wearer.”

The beauty of the system is that the reflective coating can be applied to the same socket material – a type of polymer – that is already used for sockets. The system can be used qualitatively – for the specialist to make a visual judgement on the fit. It can also be used quantitatively, recording all the details of the stresses as they change under normal movement.

Socket fit is a major problem with all prostheses – one that people have been trying to solve for decades, according to Dr John Vinney, Head of the School of Mechanical, Manufacturing and Aerospace Engineering at UWE. “Previous research has concentrated on theoretical approaches or has used invasive wires and monitors which may alter the normal gait of the patient being monitored. This method gives us accurate patient-based data.

“The techniques could be of great assistance to patients worldwide. The system could be used remotely, to analyse data captured on the other side of world.”

The two-year research project begins in January 2003, and testing and evaluation will take place in conjunction with staff and patients from the North Bristol Healthcare Trust Disablement Services Centre. The team hopes to produce a hand-held design tool that will help the prosthetist visualise and quantify what is actually going on inside a socket, so that they can improve the level of comfort for their patients. As Dr Vinney concludes: “We want to produce a device that works quickly and accurately, with the potential to dramatically improve the quality of life for a significant number of people.”