The classification of metatarsus adductus by Bleck relied on the heel bisector line (HBL). The original procedure for bisecting the heel involves the initial making of a mould of the weight bearing foot to create an ellipse image of the heel. The procedure was later simplified by using photocopies of the foot instead of moulds of the foot. In either case, the heel is then bisected to determine its longitudinal axis which is designated as the HBL. The procedure for determining the longitudinal axis of the heel in Bleck's method is unclear and fraught with potential geometric errors. This paper presents an analysis of the said geometric errors in HBL and proposes the bisection of the transmalleolar axis as a geometrically accurate alternative to the HBL to be used for the clinical assessment of metatarsus adductus.