Torque pull-out load characteristics of skull traction calipers of 'ice tong' type (with particular reference to the...

The relationship between the applied torque and the load required to pull off the calipers was established on cadavers. Torques of 0.7, 0.8 and 0.9 Newton-metres were applied to a specially adapted skull traction caliper whilst attached to the skull in the normal position when used clinically, and loads were applied in steps of 2 lb up to a maximum of 60 lb. It was found that at a torque of 0.7 Newton-metres, the caliper became detached at the maximum load, but still held during traction at torques above this value. Taking into account the fall in load with time that may occur clinically and the limiting torque for pull-out with a traction load of 60 lb, it is suggested for complete clinical safety that a torque of 0.9 Newton-metres should be applied. An open-ended torque release spanner was set for 0.9 Newton-metres for clinical use such that the compressive load is sufficient to prevent pull-out even in the unlikely event of 60 lb being applied for up to 21 days.