Reliability of clinical and radiographic measurement of rearfoot alignment in a patient population

Rearfoot alignment measures in relaxed and neutral calcaneal stance were made on eight patients using skin marking of the central bisection of the rearfoot. To assess the within-tester repeatability, measurements were made more than two weeks apart, without access to previous records. The angle of rearfoot compensation, which indicated the frontal plane movement of the rearfoot between the neutral and relaxed positions, was calculated. For the two sessions, very good agreement was evident in compensation measures for the left (r = 0.93) and right foot (r = 0.95) and the standard deviation of a single determination approximated the 0.5° measurement resolution. Using radiography, a skin marked central bisection line (50%) of the rearfoot was shown to be coincident with a line from a point 40% from the lateral side at the lower margin of the calcaneus to the mid point of its superior margin. This 40% line bisected the body of the calcaneus bone, and at the inferior end appeared coincident with the mid-point of the Achilles tendon attachment.