The reliability of clinical and caliper-based calcaneal bisection measurements

The measurements of subtalar joint neutral position and hindfoot range of motion have been shown to be unreliable. The first step in making these measurements is to determine the calcaneal bisection. This study examines the reliability of bisecting the calcaneus with digital linear calipers. Five trials on each of six cadavers resulted in a mean absolute angular difference of 0.60 degree (SD +/- 1.17 degrees). These results were then compared with results from the typical visual method used clinically. Three raters each performed five trials on six cadavers. Visual bisection was more variable, with a mean absolute error of 3.61 degrees (+/- 3.13 degrees). A mean error of 6 degrees (+/- 1 degree) is certainly possible when the heel is visually bisected. It was determined that the caliper bisection was a valid technique for bisection of the heel, but that clinical visual bisection was not.