The Midtarsal Joint (Chopart's Joint)

This is composed anteriorly of the scaphoid and cuboid bones and posteriorly by the astragalus and os calcis. The movements are not extensive and consist of flexion with inward rotation of the sole, and extension with outward rotation of the sole. The joint is separated into an inner and outer portion by an interosseous ligament where the cuboid, astragalus, and os calcis meet.

The Ligamentous Support Of The Arch Of The Foot

The bony construction of the arch or dome of the foot has already been explained (page 563). The various bones composing it are bound together not only by the short ligaments passing between contiguous bones, but the arch is strengthened by three special ligamentous structures. They are the inferior calcaneoscaphoid ligament, the plantar ligaments, long and short, and the plantar fascia.

Fig. 585. - Ligaments and tendons of the sole of the foot.

The inferior calcaneoscaphoid ligament (ligamentum calcaneonavicular plantare) runs from the lower inner portion of the scaphoid, posterior to its tubercle, to the sustentaculum tali. It is an extremely strong fibrocartilaginous band. Anteriorly and above it blends with the internal lateral ligament (deltoid) of the ankle. Together with the posterior surface of the scaphoid it forms a socket for the head of the astragalus. This ligament fills the long gap left in the inner arch of the foot between the scaphoid and os calcis. Running under and supporting it is the tendon of the tibialis posterior (Fig. 585).

The long plantar or long calcaneocuboid ligament (ligamentum piantare longian) is attached to the under surface of the os calcis in front of its tubercles and thence runs to the peroneal ridge on the cuboid bone and continues onward to the bases of the second, third, fourth, and fifth metatarsal bones. It makes a canal for the peroneus longus tendon, which runs beneath it.

The short plantar or short calcaneocuboid ligament (ligamentum calcaneo-cuboideum plantare) lies beneath the long ligament and is separated from it by a small amount of fatty tissue. It runs obliquely forward and inward from the under surface of the calcaneum to the posterior portion of the cuboid.

The Plantar Fascia (Aponeurosis Plantaris)

The middle portion of the plantar fascia runs anteriorly from the inner tubercle of the os calcis to be attached to the sides of the metatarsophalangeal articulations and bases of the proximal phalanges.

Fig. 586. - The plantar fascia.

It is a thick, strong triangular band. The outer portion is a strong band running from the external tubercle to the tuberosity of the fifth metatarsal bone. The inner portion is thin and weak (Fig. 586).

These three ligamentous structures, the calcaneoscaphoid ligament, plantar ligaments, and plantar fascia are all large, strong, fibrous structures. They join the anterior and posterior pillars of the arches like the string of a bow and prevent them from separating. When a person is standing at rest these are the main ligaments which bear the weight of the body. The static weight is borne by the ligaments but the dynamic weight (movements) is borne by the muscles.