The plantar calcaneonavicular ligament (spring ligament) is a thick, broad fibrous band that is located on the bottom portion of the foot. It connects the navicular bone's plantar (foot side) surface with the sustentaculum of the calcaneus, a shelf-like facet of the heel bone. It also provides support to the head of the talus, a bone that makes up the lower portion of the ankle joint. In doing so, the ligament bears a significant amount of body weight.
This ligament plays an important role in the development of acquired ‘flat foot deformity’ (where the arch is missing) in adults. It has been linked to the stabilization of the foot's longitudinal arch; this leads to insufficiency of the spring ligament, which causes it to tear.
The plantar calcaneonavicular ligament complex is different in different feet. Sometimes it is comprised of two ligaments, the inferior calcaneonavicular and the superomedial; however, it most often has a third ligament.