COMPUTER-ASSISTED surgery has made it easier for doctors to partially replace arthritis-wracked knees, giving patients longer lasting replacements and speeding up recovery time.

Detailed digital images, taken with the aid of infrared sensors, help surgeons accurately position implants in the knee as well as align the joint.

This minimally invasive technique was developed by Singapore surgeon Yeo Seng Jin and six other orthopaedic surgeons from Britain, the United States, Italy, the Netherlands and Australia.

The technique was designed in conjunction with software and hardware engineers from implant supplier Depuy.

Dr Yeo, 45, a senior consultant orthopaedic surgeon with the Singapore General Hospital (SGH), said: 'The prototype went through several modifications and we used the system on several cadavers first. We also had X-rays and CT scans done on our trial surgery before we performed them on actual patients.'

Dr Yeo uses this technique for partial knee replacement, an operation which removes only the most damaged areas of the cartilage and replaces these with artificial parts. He said the computer-assisted method helped reduce errors to about one degree or 1mm, 'something the human eye cannot do'.

'What the technique does is enhance the accuracy of alignment of the knee,' Dr Yeo said.

He demonstrated the technique via satellite to 117 European knee surgeons in Rome last week. He had previously displayed the technique, also via satellite, to surgeons in Barcelona.

About 1,200 knee replacement operations were carried out at SGH last year. Dr Yeo said only 15 per cent of osteoarthritic knees were suitable for partial knee replacement surgery. He has carried out 100 computer-assisted knee operations since 2004.

The patient whose operation was transmitted via satellite last Thursday was 74-year-old retiree Phay Phui Leong. He was already walking with the aid of a cane when The Straits Times visited him in the ward a day after his operation.

He said he was surprised he was able to put his weight on his left leg almost immediately.

'I went for a total knee replacement in 2002 at another hospital, using the conventional method. I had difficulty bending and straightening it and was able to flex only after going for physiotherapy for two months. I guess this time around, I will be back on the green in no time,' said the avid golfer.

However, Dr Yeo told him he has to recuperate for six weeks first.

Dr Yeo's analysis of the technique will be presented to the American Academy of Orthopaedic Surgeons 2006 annual meeting in Chicago at the end of this month.