Medial Drift of the Medial Malleolus Device. By evaluating medial displacement of the medial malleolus, this device provides important information regarding motion of the talus. By surgically embedding metal beads into the subtalar joint, Lundberg et al. (FootAnkle.1989;9:248-253) demonstrate that as the rearfoot pronates, the talus shifts medially with a “sideward rolling action,” resulting in an almost parallel translation of the talus upon the calcaneus. Measuring medial drift of the malleolus allows the practitioner to quantify the parallel translation, and this information is useful when prescribing varus and valgus posts.