With respect to the frontal plane, normal knee alignment may vary from slight genu valgum to some degree of genu varum. Because in most persons the medial femoral condyle extends farther distally than the lateral condyle, slight genu valgum tends to be more prevalent. At the hindfoot, the calcaneus should be positioned in vertical alignment with the tibia. A valgus or varus heel can usually be observed as a bowing of the Achilles tendon. A valgus positioning of the calcaneus on the talus is associated with pronation at the subtalar joint, whereas a varus hindfoot involves supination.