Knee surgery takes step up

By MARTIN JOHNSTON health reporter

Patients receiving replacement knee joints at North Shore Hospital are the first in the country to benefit from new computer technology designed to make the surgery more accurate.

The so-called knee navigation system guides the surgeon using infrared light beams and a special computer program.

A picture of the patient's knee is generated on a large computer screen near the operating table and the surgeon is shown precisely where to cut through the bones.

"It allows us to align a knee much more accurately than before," said orthopaedic surgeon Hugh Blackley, who began using the $500,000 equipment last month.

"Navigation is extremely effective in producing accurate alignment, which research shows is the key to better short- and long-term results."

Knee-joint replacement is the second most common elective orthopaedic implant procedure in New Zealand. About 3300 are performed annually, most of them on older people with arthritis.

The maker of the navigation equipment, Stryker Corporation, which also makes artificial knees, donated it to the hospital as a way of introducing it to surgeons.

Stryker's New Zealand manager, Hugh Guerin, said yesterday that these kinds of navigation systems for orthopaedic surgery were becoming common overseas.

The company was still developing a navigation system for hip replacement, but already produced one for spinal surgery.

Mr Blackley expects that within five years, this type of technology will be standard for all orthopaedic implants.

Without it, surgeons had to rely on their eyes and measuring instruments, although this produced good results for most patients, he said.

The navigation computer bounces three infrared beams off the patient's knee.

Two beams are sent from the computer itself, sited near the operating table. The third comes from a transmitter held by the surgeon or attached to his or her power-saw or other instruments.

Mr Blackley said correct alignment of a prosthetic knee joint with the patient's ankle and hip was important.

He estimated that 90 cent were aligned properly when viewed from any angle. The rest might be misaligned by up to 3 degrees, or even more in a few cases.

The misaligned joints might last for less than the 15 to 20 years expected of artificial knees. Severe misalignment, which was rare, could also restrict knee bending and cause pain.

The computer navigation system offers accuracy of within 1 degree and 1mm of proper alignment and placement.

The surgery took longer, but patients recovered faster as it was less invasive than the traditional method, Mr Blackley said.

The likelihood of some joints lasting longer was also welcome.

"The possibility of a further replacement later down the track can be a very daunting prospect for an older person."

A further benefit is that one of the risks of the traditional operation, a piece of fat being dislodged from within the leg bones and blocking a lung blood vessel, is eliminated since holes no longer need to be drilled deep into the tips of the leg bones. This is because the computer replaces the need to insert alignment rods into these bones.