Thermal damage done to bone by burring and sawing with and without irrigation in knee joint replacement

Orthopaedic tools which resect bone in procedures such as total knee replacement (TKR) generate heat, causing a temperature rise at the resected surface. When bone temperature exceeds 47°C for >60 seconds irreversible changes known as osteonecrosis develop. Osteonecrosis has been found to increase rates of aseptic implant loosening and implant failure. With computer assisted surgery becoming more common in orthopaedics, burrs are being increasingly used. This study aimed to compare the traditional oscillating saw to the burr in terms of temperature generation, and thermal damage done to bone health. The effectiveness of irrigating bone to reduce bone temperature was also investigated. Bovine femora were burred and sawed with or without irrigation, and bone temperatures were recorded with a visual infrared thermometer. Two cooling agents were used; one at room temperature, and a second at 4°C. After cutting, samples were removed for histomorphometric analyses. Percentages of non-viable osteocytes at the cut surface were calculated, and minimum depths of thermal damage done by both cutting tools were estimated. Statistical analyses were carried out to test differences between groups (α = 0.05). Burring was more likely to produce temperatures of >47°C for >60 seconds than sawing. Mean and maximum temperatures also tended to be higher when burring. However, there were no statistical differences between the temperatures generated when sawing and burring (p > 0.05). Irrigated bone had lower temperatures, higher percentages of viable osteocytes, and smaller thermal damage depths (p 60 seconds irreversible changes known as osteonecrosis develop. Osteonecrosis has been found to increase rates of aseptic implant loosening and implant failure. With computer assisted surgery becoming more common in orthopaedics, burrs are being increasingly used. This study aimed to compare the traditional oscillating saw to the burr in terms of temperature generation, and thermal damage done to bone health. The effectiveness of irrigating bone to reduce bone temperature was also investigated. Bovine femora were burred and sawed with or without irrigation, and bone temperatures were recorded with a visual infrared thermometer. Two cooling agents were used; one at room temperature, and a second at 4°C. After cutting, samples were removed for histomorphometric analyses. Percentages of non-viable osteocytes at the cut surface were calculated, and minimum depths of thermal damage done by both cutting tools were estimated. Statistical analyses were carried out to test differences between groups (α = 0.05). Burring was more likely to produce temperatures of >47°C for >60 seconds than sawing. Mean and maximum temperatures also tended to be higher when burring. However, there were no statistical differences between the temperatures generated when sawing and burring (p > 0.05). Irrigated bone had lower temperatures, higher percentages of viable osteocytes, and smaller thermal damage depths (p < 0.05). Uncooled saline was successful at reducing mean temperatures <47°C in sawed bone, however cooled saline was needed when burring (p < 0.05). Hence, to reduce the risk of osteonecrosis, cooled irrigation should be used when resecting bone in procedures such as TKR, especially when burring. By irrigating bone during such procedures, it is hoped that implant failure rates could be reduced