Set screw break-off study in spinal neurosurgery.

摘要

This thesis describes the measurement of high g-forces, in the range of 400-800g's occurring in a spinal construct during the breaking of the set-screw head using a manual torquing instrument. The measurements were validated using a high speed camera. The design torque (11 N-m) required for breaking the set-screw was compared with the torque calculated from the distortion energy theory for material fracture (9.9 N-m) and an actual measurement using a torque wrench (11.3 N-m). A comparison between the manual and powered instruments showed a 27.68% reduction in g-forces and a 36.42% reduction in die-down time while using the powered instrument. 8.52% less energy was felt on the adjoining screw. The consistency in the powered instrument is higher because the standard deviation using the manual instrument is 8.46, compared to the powered instrument which was 8.31. Also 25g's was recorded on the surgeon's wrist and elbow. Based on previous work done, the external work done by the surgeon was about 60-120 KJ. The onset of fatigue was apparent in consecutive break events as illustrated by the change in EMG parameters over time.