The biomechanics group is one of Imperial's biggest patent sources, covering products such as artificial elbows, knees, shoulders and ankles.

Andrew Amiss heads the group and one of his research projects is looking into ways of improving the treatment of knee injuries. Sports such as football and skiing are a frequent cause of these injuries.

Severe twisting of the knee or unusual loading of the joint can cause ligament damage. Ligaments are made of bands of collagen.

The knee ligaments hold together the tibia and the femur. One group, called the cruciate ligaments, pass through the knee joint and do not heal if broken, partly because of poor blood supply.

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Conventional surgical solutions for cruciate ligament failures involve grafting collagen taken from elsewhere in the body, typically hamstring or a strip of patella tendon from the knee. "The biggest problem for the surgeon is deciding where to place the graft because it is difficult to access the attachment sites within the knee," said Dr Amiss.

In the case of the patella tendon, the length of tendon removed will also have bits of bone at the ends. These act as a plug that is jammed into a hole drilled into the knee and tightened with a screw.

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Hamstring grafts are threaded through the holes on to the bone and clamped with a screw and washer.

But despite medical advances, many uncertainties remain: "The tension of the graft has to be correct. It plays a big role in how the knee heals but we still don't know what the tension should be. The length of graft is also very important but there is a huge variation in the looseness of the joint from person to person. We are trying to abolish any abnormal movement of the joint. Even a few millimetres of abnormal motion can cause real problems, allowing the tibia to slip out from beneath the femur, and the knee gives way," said Dr Amiss.

His group is experimenting with sensors attached to bones of dead knees to monitor movement after the joints have been reconstructed. Dr Amiss, whose work is funded by the Arthritis and Rheumatism Council, has had ethical permission to use sensors on patients' knees during operations to check for abnormal joint motion.