Accuracy and reliability of torque wrenches used for halo application in children

Halo ring and vest application in children requires torque wrenches capable of delivering a spectrum of torque values ranging from 0.11 to 0.68 N-m (1 to 6 in-lb). Published evaluations of torque wrenches commonly used in adults have shown that the measured torque values were within 10% of the target torque in only 64% of trials. The objective of the present study was to evaluate the accuracy, reliability, and interobserver variability of halo wrenches capable of applying the lower torque levels commonly used in children.

Torque wrenches from four distributors (Bremer, Jerome Medical, Mountz, and PMT) were tested with use of a calibrated torque-meter. Five wrenches of each type were tested by a single observer, with fifty trials performed at six different torque settings (0.11, 0.23, 0.34, 0.45, 0.57, and 0.68 N-m). One wrench of each type was then tested by two additional observers at a torque setting of 0.34 N-m, with each observer performing fifty trials per wrench.

The measured torque value was within 10% of the target value in 69.2% of the 6400 trials, including 50.7% of the trials performed with the PMT wrench, 51.8% of those performed with the Bremer wrench, 84.5% of those performed with the Mountz wrench, and 90% of those performed with the Jerome wrench. Significant variability (p < 0.05) was found between at least two, and as many as five, wrenches of the same variety at each of three torque settings used for comparison (0.23, 0.45, and 0.68 N-m). Significant interobserver variability (p < 0.05) was found between at least two observers during testing of the Jerome and Mountz wrenches, but no significant differences were shown between observers during testing of the PMT and Bremer wrenches.

The Jerome and Mountz wrenches are more accurate and reliable at low torque settings than the PMT and Bremer wrenches are. Variability among different wrenches from the same manufacturer may be seen with any of the wrenches studied.