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In many ways, MP3 players have gone above their call of duty as music storing devices, and are often used to help bring criminals to justice, record flight data, etc. Now, they are being used to assist orthopaedic surgeons in knee-replacement procedures. For the first time in Asia, a city doctor on Wednesday performed a knee-replacement computer-assisted surgery on an elderly patient-with an iPod. 

The patient, 75-year-old Gulab Singhvi, had been suffering from severe joint pain in her left knee for the past four years. When she decided to undergo a knee-replacement procedure, little did her family realize that Singhvi would be the first person in Asia to undergo the surgery with the help of an iPod navigation system. 

Dr Arun Mullaji, who performed the surgery at Breach Candy Hospital, said: "Though the computer navigation itself was a breakthrough, the iPod navigation allows for better accuracy." 

So how does it work? The hardware is made up of a special casing for the iPod as well as a computer system that communicates wirelessly with the device. The computing system also comprises a camera equipped with an infrared sensor. The casing has slots for miniature instruments and three antennae with reflecting spheres. These spheres provide a frame of reference to the camera's infrared sensor, which tracks each of them to plot the x, y and z axis of each point. (See Cutting Edge box). 

This system, which has been developed by Smith & Nephew Inc, works on a similar technology used in computer navigation systems. "The iPod is connected to a camera attached to a stand which is kept at a distance. Instead of a screen, which used to be at the same stand earlier, the surgeon can see the image along with other information on the iPod screen," said Tim Frandsen, director of global surgical navigation in the company. 

Mullaji added: "The iPod screen shows accurate measurements, angles, positions and the movement that will be possible for each point touched by the sensor pointer connected to it. And since the iPod is carried by us in hand, the screen is at the same area where the surgery is being done as against the screen at a distance in a computer navigation system."- 

In a replacement surgery, there's a 3 mm margin of error. If there is an error beyond this, the person may suffer multiple fractures and dislocations even after the surgery. "Studies prove that within the next 30 years, there is likely to be a 600% increase in the number of revision surgeries world over. The iPod navigation system helps in giving the alignment of the bone joint with 0.1 mm precision," said Mullaji.