A biomechanical study of torque and accuracy of halo pin insertional devices

The purpose of the present study was to assess the accuracy and repeatability of the torque achieved with a variety of devices used for the insertion of halo pins. We found that equivalent devices from the same manufacturer did not reliably achieve the same torque, that the same device used by different surgeons did not reliably achieve the same torque, and that the devices achieved varying levels of accuracy and repeatability. The proportion of trials in which the achieved torque was within +/- 10 per cent of the intended torque averaged 64 per cent (range, less than 1 to 100 per cent). Our data suggest that the insertion of halo pins with use of most currently available torque-setting devices is an inherently inaccurate process.