Bone saws are causing more damage than necessary, an engineering student has found, writes Dick Ahlstrom
Surgeons using bone saws may be causing more tissue damage than realised. The heat of friction when using these saws causes bone-cell death that can weaken surrounding bone and delay healing.
Master's engineering graduate Hamid Khalili Parsa recently completed his part in a research project at Sligo Institute of Technology studying the sharpness of surgical instruments. The work, under research supervisor Ger Reilly, is in partnership with Trinity College Dublin, University College Dublin and surgeons at Sligo General Hospital.
As part of this effort, Parsa developed a technique for measuring temperature rises caused by friction in the cutting zone and used this to show how far from the blade that bone would be damaged. Obviously the sharper the blade the faster the cut and the less frictional heat. His work showed the complex interplay between cutting speed, temperature and blade sharpness.
Parsa, an electronics engineering graduate from Iran, used thermal sensors to measure the distance from the cutting region that heat travels through the bone. Bovine bone was used for these tests.
Bone-cell death occurs at temperatures above 44 degrees, but the heat generated from friction exceeded this temperature, he explains.
"There is a region of bone of at least 9mm on either side of the cut where bone-cell death will occur," he says. "All of the experiments I did on bone showed the temperature exceeded the 44 degree limit."
Damage beyond this zone is a possibility however. "I didn't have enough sensors. If I had more sensors it could be more than 9mm. That is really important. It has huge implications for hospitals."
When cutting bone with a reciprocating saw, the lowest cutting temperatures occurred at a cutting rate of 2mm per minute. While the finding suggests this rate is optimal to reduce heat of friction, this is not the best blade cutting speed to get the best cut. And as blades become dull, heat of friction rises.
"The effect of overheating bone from friction causes necrosis or death in the adjacent bone, which can lead to problems of union, for example, if trying to plate a bone after an operation," says Sligo General Hospital consultant orthopaedic surgeon Andrew Macey.
A scanning electron microscope was used to examine the saw blades to see how quickly they became blunt and needed replacement.
Surgeons typically use saw blades up to 10 times before replacement, but the microscopy work showed that blades actually needed replacement after each use, says Parsa. The blades themselves cost about €75 each.
The findings have implications for hospitals and orthopaedic surgeons by highlighting the need for frequent saw replacement.
"The research has shown that blades need to be replaced after each use, but they are frequently used many more times in operating theatres," says Parsa. "I suggested to all the surgeons in Sligo hospital they should replace the blades after each use."
Parsa completed his master's degree and has now begun a PhD on biomechanics and bioengineering at University College Dublin. He would like to pick up on the bone research at some stage however. "My long-term aim is to make a coated blade that would reduce friction," he says.