Purpose: Thermal injury to the optic nerve is a potential complication of bony decompression of the orbital apex. An animal model was used to compare and contrast temperature change while removing orbital bone with ultrasonic and conventional drills. Methods: Two devices, Sonopet ultrasonic bone curette and TPS CORE Micro drill, were used to remove bone from six unpreserved exenterated porcine orbits at fixed distances from the optic canal while temperature was recorded. Increasing irrigation flow rate and decreasing saline temperature with the ultrasonic bone curette were also investigated. Results: The mean change in temperature at the optic canal using the ultrasonic bone curette with 18 ml/min 24°C irrigation was +7.2 ± 3.3°C (range 3.3-12.7°C) at 60 s, and using the rotational drill was +1.7 ± 1.3°C (range 0.1-3.3°C), representing a statistically significant increase above baseline for both drills (p < 0.01 for each). The difference in temperature change between drills was statistically significant (p < 0.01). When irrigation fluid was changed from room temperature saline (24°C), rate 18 ml/min to chilled (10°C) irrigation saline, rate 40 ml/min, the magnitude of the mean temperature increase was reduced by 3.1°C, p < 0.05. Conclusions: In this orbital decompression model, both ultrasonic and rotational drills induced a rise in temperature. This increase was significantly greater with the ultrasonic bone curette, measuring up to 13.7°C. Clinicians should be aware of the potential for temperature spikes when decompressing the orbital apex. Increasing irrigation flow rate and using chilled saline may mitigate increases in temperature.
Keywords: Graves disease; Orbital decompression; bone drill; ultrasonic drill.