Plantar calcaneonavicular ligament

The plantar calcaneonavicular ligament (Spring ligament; Inferior or internal calcaneonavicular ligament; calcaneonavicular ligament; ) is a broad and thick band of fibers, which connects the anterior margin of the sustentaculum tali of the calcaneus to the plantar surface of the navicular.

This ligament not only serves to connect the calcaneus and navicular, but supports the head of the talus, forming part of the articular cavity in which it is received.

The dorsal surface of the ligament presents a fibrocartilaginous facet, lined by the synovial membrane, and upon this a portion of the head of the talus rests.

Its plantar surface is supported by the tendon of the Tibialis posterior;

Its medial border is blended with the forepart of the deltoid ligament of the ankle-joint.

The plantar calcaneonavicular ligament, by supporting the head of the talus, is principally concerned in maintaining the arch of the foot. When it yields, the head of the talus is pressed downward, medialward, and forward by the weight of the body, and the foot becomes flattened, expanded, and turned lateralward, and exhibits the condition known as flat-foot.

As this ligament contains a considerable amount of elastic fibers, it was believed to give elasticity to the arch and spring to the foot; hence it has been sometimes called the "spring" ligament. But it is actually considered that this ligament is relatively few elastic and is not evolved in the mouvement of the foot, especially during spring mouvements. The spring ligament mainly provide static support to the medial longitudinal arch and stabilize the talonavicular joint

It is supported, on its plantar surface, by the tendon of the Tibialis posterior, which spreads out at its insertion into a number of fasciculi, to be attached to most of the tarsal and metatarsal bones. This prevents undue stretching of the ligament, and is a protection against the occurrence of flat-foot; hence muscular weakness is, in most cases, the primary cause of the deformity.

The spring ligament may be subdivided in different ligamentous portions, the most widely accepted anatomical description identifies three main components:

1. Superomedial calcaneonavicular ligament (SMCNL): This is the thickest and most robust portion, lying superomedially and supporting the head of the talus. It contains a fibrocartilaginous articular facet and is histologically adapted for significant load bearing.

2. Medioplantar oblique ligament (MPO): This component runs obliquely from the calcaneus to the navicular, located medioplantarly beneath the SMCNL. It is thinner and less consistently visualized on imaging, but is present in the majority of cases.

3. Inferoplantar longitudinal ligament (IPL): This ligament runs longitudinally along the inferoplantar aspect of the complex, from the calcaneus to the navicular. It is the thickest of the plantar components and is consistently identified in anatomical and imaging studies.