Spring ligament is an alternative name for the plantar calcaneonavicular ligament, a ligament of the foot. Linking the calcaneus, or heel bone, to the navicular, a bone of the tarsus in the midfoot, this ligament is a thick band of fibrous connective tissue found near the plantar surface or sole of the foot. Along with the long plantar and short plantar ligaments, it is considered a part of the spring ligament complex, which not only supports the arch of the foot but also absorbs a large percentage of a person’s body weight.
The plantar calcaneonavicular ligament originates on the front portion of the heel bone known as the sustentaculum tali. An irregularly shaped bone, the heel bone, or calcaneus, features several plateau-like surfaces for articulation with adjacent bones, such as the talus above it. One such facet is the sustentaculum tali, which is situated near the top of the calcaneus along its medial or inside surface. It is along this horizontal facet that the spring ligament arises, as do the tibiocalcaneal and medial talocalcaneal ligaments.
From the heel bone, the spring ligament stretches forward, along the underside of the foot on the side of the big toe. It attaches to the navicular bone, a bone of the tarsus. The tarsus is a cluster of seven irregularly shaped bones in the mid and hind foot behind the metatarsals, the long bones of the foot that connect to the toes. Situated to the front of the talus on the medial aspect of the foot, the navicular features a concave bottom surface to which the plantar calcaneonavicular ligament attaches.
The main function of the spring ligament is to hold these two bones together and support the joint between them, a type of synovial or fluid-filled joint known as an arthrodial or planar joint, in which the adjacent flat surfaces of two or more adjoining bones may slide slightly past one another. Within this intertarsal joint, in which both the calcaneus and talus bones join with the navicular, the convex head of the talus articulates with the concave posterior surface of the navicular. As the plantar calcaneonavicular ligament runs beneath the navicular, it helps support the head of the talus within the joint. Likewise, it forms the lower border of the joint and helps to contain the contents of the synovial cavity inside. Finally, it spans a portion of the medial arch of the foot, contributing to the elasticity of the arch and thereby absorbing weight distributed from the heel bone across the arch to the ball of the foot.