Investigation of how different halos influence pin forces.

STUDY DESIGN: This study investigated the effect of the size and material of halo rings on the pin force produced at the halo pin-calvarium complex. SUMMARY OF BACKGROUND DATA: Loosening of halo pins has been a problem with using the halo-vest apparatus to stabilize cervical spine fractures. METHODS: One standard halo pin and seven different halo rings were used to test the anterior pin hole of each ring at a constant torque of 8 inch-pounds (0.9 Nm). RESULTS: Pin force fluctuated from halo to halo, and decreased as the nut was tightened. CONCLUSIONS: Identical torques applied to different halos will not guarantee the same magnitude of pin force for halo fixation.