Reliability after repeated use of a torque screwdriver employed for halo pin fixation

It has been recommended that halo torque screwdrivers be used only once. To determine if this advice is justified on biomechanical grounds, five commercially available torque screwdrivers were cycled 1,600 times each in an Instron testing machine over a 7-day period. The screwdrivers displayed an initial error from the dial reading at both 6 and 10 in-lb of only +/- 0.3 in-lb. After cyclic loading and retesting, the percent deviation from original calibration was 8% at both 6 and 10 in-lb. These data demonstrate the accuracy and dependability of the torque screwdrivers and imply that repeated use of these devices should be safe.