Mechanical engineers at Imperial College are developing a robot that promises to help surgeons lessen their reliance on an array of jigs and fixtures and achieve greater accuracy when carrying out the complex task of replacing knees with prosthetic implants.

The work is being carried in collaboration with Justin Cobb of Middlesex Hospital and is directed at both total knee replacement and partial knee replacement, usually the inner half of the knee. The project is backed by the Wishbone Trust.

Roger Hibberd, one of the researchers at Imperial, says the system could eventually help to dramatically reduce the scale of the knee openings that surgeons have to make in order to carry out replacement operations, thereby minimising trauma of the knee.

At present, surgeons cut as accurately as they can and then try to match different prosthesis to the cut according to best fit. The robot being developed could overcome such uncertainty.

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But it is not intended that the robot would replace the surgeon. Dr Hibberd says: "The surgeon would still carry out the cutting but the robot would have an inbuilt 'barrier' which would restrict the allowable area of cutting." In cutting a flat surface therefore, the robot would not allow the surgeon to stray outside the area or exceed the depth of cut designated by its programme. "The important thing is that the surgeon still has the 'feel' of the operation through being able to see and hear what is going on," he says.

Brian Davies, another member of the Imperial team, explains that in practice, the surgeon holds the cutter motor which is fixed at the end of the robot's arm. The system allows surgeons implicit force control with resistance being provided by the robot when designated limits to cutting operation are reached. The surgeon can therefore feel the cutting forces and, if necessary, take lighter or slower cuts. Planes, grooves or holes can be machined using this procedure.

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Dr Hibberd says that a major problem now exercising the researchers is the development of accurate computer models of the cuts needed.