Foot

The foot (pes) is divided into 3 sections: the tarsus, metatarsus and toes. The skeleton of these sections is the bones of the tarsus (ossa tarsi), the bones of the metatarsus (ossa metatarsalia) and the bones of the toes (ossa digitorum pedis).

The tarsal bones. The tarsus consists of seven spongy bones arranged in two rows. The proximal (back) row consists of two large bones: the talus and the calcaneus. The remaining five tarsal bones form the distal (front) row.

The talus has a body (corpus tali), a head (caput tali) and a narrow connecting part - the neck (collum tali). On the upper surface is the trochlea tali, consisting of three articular surfaces. The upper surface (facies superior) is intended for articulation with the lower articular surface of the tibia. The articular surfaces lying on the sides of the trochlea: the medial malleolar surface (facies malleolaris medialis) and the lateral malleolar surface (facies malleolaris lateralis) - articulate with the corresponding articular surfaces of the malleoli of the tibia and fibula. On the lateral surface of the body is the lateral process of the talus (processus lateralis tali).

Behind the block, the posterior process of the talus (processus posterior tali) extends from the body of the talus. A groove for the tendon of the long flexor of the big toe is visible on the process. On the underside of the talus there are three articular surfaces for articulation with the calcaneus: the anterior, middle, and posterior calcaneal articular surfaces (faciei articulares calcanei anterior, media et posterior). Between the middle and posterior articular surfaces there is a groove for the talus (sulcus tali). The head of the talus is directed forward and medially. The rounded navicular articular surface (facies articularis navicularis) serves to articulate it with the navicular bone.

The calcaneus is the largest bone in the foot. It is located under the talus and protrudes significantly from underneath it. At the back of the body of the calcaneus, a downward-sloping calcaneal tubercle (tuber calcanei) is visible. On the upper side of the calcaneus, three articular surfaces are distinguished: the anterior, middle, and posterior talar articular surfaces (faciei articulares talaris anterior, media et posterior). These surfaces correspond to the calcaneal articular surfaces of the talus. Between the middle and posterior articular surfaces, the calcaneal groove (sulcus calcanei) is visible, which, together with a similar groove on the talus, forms the sinus of the tarsus (sinus tarsi). The entrance to this sinus is located on the dorsum of the foot on its lateral side. A short and thick process, the support of the talus (sustentaculum tali), extends from the anterior superior edge of the calcaneus on the medial side. On the lateral surface of the calcaneus there is a groove for the tendon of the long peroneal muscle (sulcus tendinis m.peronei longi). On the distal (anterior) end of the calcaneus there is a cuboid articular surface (facies articularis cuboidea) for articulation with the cuboid bone.

The navicular bone (os naviculare) is located medially, between the talus behind and the three cuneiform bones in front. Its proximal concave surface articulates with the head of the talus. On the distal surface of the navicular bone there are three articular surfaces for articulation with the cuneiform bones. At the medial edge is the tuberosity of the navicular bone (tuberositas ossis navicularis) - the attachment site of the posterior tibialis muscle.

The sphenoid bones (ossa cuneiformia) - medial, intermediate and lateral - are located in front of the navicular bone. The medial sphenoid bone (os cuneiforme mediale), the largest, articulates with the base of the first metatarsal bone. The intermediate sphenoid bone (os cuneiforme intermedium) articulates with the second metatarsal bone, the lateral sphenoid bone (os cuneiforme laterale) - with the third metatarsal bone.

The cuboid bone (os cuboideum) is located in the lateral part of the foot, between the calcaneus and the last two metatarsal bones, with which it forms joints. On the medial side of the cuboid bone is the articular surface for the lateral cuneiform bone, and a little behind - for articulation with the navicular bone. On the lower (plantar) side of the cuboid bone is the groove of the tendon of the long peroneal muscle (sulcus tendinis m. peronei longi).

Metatarsal bones (ossa metatarsi). They include five tubular short bones. The shortest and thickest is the 1st metatarsal bone, the longest is the 2nd. Each bone has a body (corpus), head (caput) and base (basis). The bodies of the metatarsal bones have a convexity facing the back. The bases are equipped with articular surfaces for articulation with the bones of the tarsus. The head of the 1st metatarsal bone is divided on the plantar side into two platforms, to which the sesamoid bones are adjacent. The base of the 1st metatarsal bone forms a joint with the medial cuneiform bone. The bases of the 2nd and 3rd bones articulate with the intermediate and lateral cuneiform bones, and the bases of the 4th and 5th metatarsal bones - with the cuboid bone. On the lateral side of the 5th metatarsal bone is the tuberosity of the 5th metatarsal bone (tuberositas ossis metatarsals) for attachment of the peroneus brevis muscle.

The toes, like the fingers, have a proximal phalanx (phalanx proximalis), a middle phalanx (phalanx media), and a distal phalanx (phalanx distalis). The skeleton of the first toe (hallux) consists of only two phalanges: proximal and distal. The phalanges have a body, a head, and a base. The base of each proximal phalanx has a flattened fossa, which serves for articulation with the head of the corresponding metatarsal bone. At the base of the middle and distal phalanges there are fossae for articulation with the head of the phalanx located more proximally. Each distal (nail) phalanx ends in a tubercle (tuberositas phalangis distalis).

The tarsal and metatarsal bones do not lie in the same plane. The talus is located on the calcaneus, and the navicular bone is higher than the calcaneus and cuboid bones. The bones of the medial edge of the tarsus are raised compared to its lateral edge. With this mutual arrangement of the bones, the arches of the foot are formed, which provide springy support for the lower limb. The arch of the foot has a convexity facing upward. The lateral edge of the foot is lower than the medial, which is slightly raised and open to the medial side. In fact, only a few points in the foot serve for support: the tubercle of the calcaneus - at the back, the heads of the metatarsal bones, mainly I and V, - at the front. The phalanges of the fingers only slightly touch the ground.

The foot as a whole. The foot is adapted to perform a supporting function, which is facilitated by the presence of "tight" joints and powerful ligaments. The bones of the foot are connected, forming arches convex upwards, oriented in the longitudinal and transverse directions. All five longitudinal arches begin on the calcaneus, fan-shaped forward, along the tarsal bones to the heads of the metatarsal bones. In the transverse direction, all arches have different heights. At the level of the highest points of the longitudinal arches, an arched transverse arch is formed. Due to the archedness, the foot does not rest on the entire surface of the sole, but constantly has three points of support: the calcaneal tubercle, the heads of the first and fifth metatarsal bones in front.

The arches of the foot are held in place by the shape of the adjacent bones, ligaments (the so-called passive "tightening" of the arches) and muscle tendons (active "tightening"). The most powerful passive tightening of the longitudinal arches of the foot are the long plantar ligament, the plantar calcaneonavicular and other ligaments. The transverse arch of the foot is strengthened by the deep and transverse metatarsal and other ligaments located in the transverse direction.