The tarsal bones [ossa tarsi] are grouped in two rows: - a proximal row, consisting of the talus and calcaneus, and a distal row, consisting of four bones which, enumerated from tibial side, are the first, second, and third cuneiform bones and the cuboid. Interposed between the two rows on the tibial side of the foot is a single bone, the navicular; on the fibular side the proximal and distal rows come into contact.

Compared with the carpus, the tarsal bones present fewer common characters, and greater diversity of size and form, in consequence of the modifications for sup- porting the weight of the trunk. On each, however, six surfaces can generally be recognized, articular when in contact with neighboring bones, elsewhere sub- cutaneous or rough for the attachment of ligaments. As regards ossification, they correspond in the main with that of the bones of the carpus. Each tarsal bone is ossified from a single center, but the calcaneus has, in addition, an epiphysis for a large part of its posterior extremity, and the talus, an occasional center for the os trigonum.

The Talus

The talus (or astragalus) is, next to the calcaneus, the largest of the bones of the tarsus. Above it supports the tibia, below it rests on the calcaneus, at the sides it articulates with the two malleoli, and in front it is received into the navicular. For descriptive purposes, it may be divided into a head, neck, and body.

The left foot (superior surface.)

The body is somewhat quadrilateral in shape. The upper surface presents a broad, smooth surface for the tibia, slightly concave from side to side, convex from before backward, and wider in front than behind. "The diminution in width posteriorly is associated with an obliquity of the lateral margin, which is directed medially as well as backward and downward. The inferior surface is occupied by a transversely disposed oblong facet [facies articularis calcanea posterior], deeply concave from side to side, which articulates with a corresponding surface on the calcaneus. Of the malleolar surfaces, the lateral is almost entirely occupied by a large triangular facet, broad above, where it is continuous with the superior surface, concave from above downward, for articulation with the lateral malleolus; on the medial malleolar surface is a pyriform facet continuous with the superior surface, broad in front and narrow behind, which articulates with the medial malleolus. Below this facet the medial surface is rough for the attachment of the deep fibers of the deltoid (internal lateral) ligament of the ankle. The superior surface and the two malleolar surfaces together constitute the trochlea. The poste- rior Surface is of small extent and marked by a groove which lodges the tendon of the flexor hallucis longus. Bounding the groove on either side are two tubercles, of which the lateral [processus posterior tali] is usually the more prominent, for attachment of the posterior talo-fibular ligament of the ankle-joint; the medial tubercle gives attachment to the medial talo-calcaneal ligament. Continuous, with the anterior aspect of the body is the neck, a constricted part of the bone supporting the head. Above it is rough, and perforated by numerous vascular foramina. Below, it presents a deep groove [sulcus tali], directed from behind forward and lateralward. When the talus is articulated with the calcaneus, this furrow is converted into a canal [sinus tarsi] in which is lodged the interosseous talo-calcaneal ligament. The head is the rounded anterior end of the bone, and its large articular surface is divisible into three parts: in front, a smooth, oval convex area, directed downward and forward for the navicular bone; below, an elongated facet, convex from front to back, for articulation with the sustentaculum tali of the calcaneus; and between these, is a small facet which rests on the calcaneo-navicular ligament, separated from it by the synovial membrane of the talo-calcaneo-navicular joint.

The left foot plantar surface (inferior.)

Articulations of the talus

The talus articulates with four bones and two ligaments. Above and medially with the tibia, below with the calcaneus, in front with the navicular, laterally with the fibula. The head articulates with the calcaneo-navicular ligament and the lateral border of the superior surface, at its posterior part, with the transverse ligament of the inferior tibio-fibular joint.

The talus is a very vascular bone and is nourished by the dorsalis pedis artery and its tarsal branch. It gives attachment to no muscles.

Ossification

The talus is ossified from one, occasionally from two, nuclei. The principal center for this bone appears in the middle of the cartilaginous talus at the seventh month of intra-uterine life. The additional center is deposited in the posterior portion of the bone, and forms the lateral posterior tubercle which may remain separate from the rest of the bone and form the os trigonum. At birth, the talus presents some important peculiarities in the disposition of the articular facet on the tibial side of its body, and in the obliquity of its neck. If, in the adult talus, a line be drawn through the middle of the superior trochlear surface parallel with its medial border, and a second line be drawn along the lateral side of the neck of the bone so as to intersect the first, the angle formed by these two lines will express the obliquity of the neck of the bone. This in the adult varies greatly, but the average may be taken as 10°. In the fetus at birth the angle averages 35°, whilst in a young orang it measures 45°. In the normal adult talus, the articular surface on the tibial side is limited to the body of the bone. In the fetal talus, it extends for some distance on to the neck, and sometimes reaches almost as far forward as the navicular facet on the head of the bone. This disposition of the medial malleolar facet is a characteristic feature of the talus in the chimpanzee and the orang. It is related to the inverted position of the foot which is found in the human fetus almost up to the period of birth, and is of interest to the surgeon in connection with some varieties of club-foot. (Shattock and Parker.)

View of the right talus

a superior surface for tibia - d neck- e head - f for scaphoid - g groove for the flexor halucis longus

 

 

 

 

 

The Calcaneus bone

The calcaneus (or os calcis) is the largest and strongest bone of the foot. It is of an elongated form, flattened from side to side, and expanded at its posterior extremity, which projects downward and backward to form the heel. It presents six surfaces, superior, inferior lateral, medial, anterior and posterior.

The superior surface presents in the middle a large, oval, convex, articular facet for the under aspect of the body of the talus. In front of the facet the bone is marked by a deep depression, the floor of which is rough for the attachment of ligaments, especially the talo-calcaneal, and the origin of the extensor digitorum brevis muscle; when the calcaneus and talus are articulated, this portion of the bone forms the floor of a cavity called the sinus tarsi. Medi- ally, the upper surface of the bone presents a well-marked process, the sustentaculum tali, furnished with an elongated concave facet, occasionally divided into two, for articulation with the under aspect of the head of the talus. The posterior part of the upper surface is non- articular, convex from side to side, and in relation with a mass of fat placed in front of the tendo Achillis.

The inferior surface is narrow, rough, uneven, and ends posteriorly in two processes: the medial is the larger and broader, the lateral is narrower but prominent. The medial process affords origin to the abductor hallucis, the flexor digitorum brevis, and the abductor digiti quinti; the last muscle also arises from the lateral process and from the ridge of bone between. The rough surface in front of the tubercles gives attachment to the long plantar ligament (calcaneo- cuboid) and the lateral head of the quadratus plantae. Near its anterior end this surface forms a rounded eminence, the anterior tubercle, from which (as well as from the shallow groove in front) the plantar (short) calcaneo-cuboid ligament arises. (According to the BNA nomenclature, the medial and lateral processes belong to the tuber calcanei or the posterior extremity of the bone.)

The lateral surface is broad, flat, and slightly convex. It represents near the middle a small eminence for the calcaneo-fibular ligament of the ankle-joint. Below and in front of this is a well-marked tubercle - the trochlear process [processus trochlearis] (or peroneal tubercle), separating two grooves, the upper for the peroneus brevis and the lower for the peroneus longus.

The medial surface is deeply concave, the hollow being increased by the prominent medial process behind and the overhanging sustentaculum tali in front. The latter forms a prominence of bone projecting horizontally, concave and articular above, grooved below for the tendon of the flexor hallucis longus, and giving attachment to a slip of the tendon of the tibialis posterior, the inferior calcaneo-navicular ligament, and some fibers of the deltoid ligament of the ankle-joint. The hollow below the process receives the plantar vessels and nerves and its lower part gives attachment to the medial head of the quadratus planice.

The anterior surface is somewhat quadrilateral in outline with rounded angles, and presents a saddle-shaped articular surface for the cuboid.

The posterior surface is oval in shape, rough, and convex. It is divided into three parts: - an upper, smooth and separated by a bursa from the tendo Achillis; a middle part giving attachment to the tendo Achillis and the plantaris, and a lower part in relation to the skin and fat of the heel. The expanded posterior extremity of the bone is known as the tuber calcanei.

Articulations

The calcaneus articulates with two bones, the talus above and the cuboid in front.

Blood-supply

The calcaneus is nourished by numerous branches from the posterior tibial and the medial and lateral malleolar arteries. They enter the bone chiefly on the inferior and medial surfaces.

Appears at the tenth, and unites at the sixteenth year

Ossification

The primary nucleus appears in the sixth month of intra-uterine life. The epiphysis, for its posterior extremity, begins to be ossified in the tenth year and is united to the body of the bone by the sixteenth year. It may extend over the whole of the posterior surface, or over the lower two-thirds only, leaving a part above in relation to the bursa beneath the tendo Achillis, which is formed from the primary nucleus. The medial and lateral processes are formed by the epiphysis.

View of the right calcaneus

a for talus - c calcaneus groove -  b medial process

The Navicular bone

The navicular [os naviculare pedis] is oval in shape, flattened from before backward, and situated between the talus behind and the three cuneiform bones in front. It is characterized by a large oval, concave, articular facet on the posterior surface, which receives the head of the talus; a broad, rough, rounded eminence on the medial surface, named the tuberosity of the navicular, the lower part of which projects downward and gives insertion to the tendon of the tibialis posterior; and an oblong-shaped anterior surface, convex and divided by two vertical ridges into three facets which articulate with the three cuneiform bones. The superior (dorsal) surface is rough, convex, and slopes downward to the tuberosity; the inferior (plantar) surface is irregular and rough for the attachment of the inferior calcaneo-navicular ligament, and the lateral surface is rough and sometimes presents a small articular surface for the cuboid.

Articulations

With the talus behind, with the three cuneiform bones in front, and occasionally with the cuboid on its lateral aspect.

Ossification

The nucleus for the navicular appears in the course of the fourth year. The tuberosity of the navicular, into which the tibialis posterior acquires its main insertion, occasion- ally develops separately, and sometimes remains distinct from the rest of the bone.

View of the navicular

The Cuneiform Bones

Of the three cuneiform bones, the first is the largest, the second is the smallest, and the third intermediate in size. They are wedge-shaped bones placed between the navicular and the first, second and third metatarsal bones. Posteriorly, the ends of the bones lie in the same transverse line, but in front, the first and third project farther forward than the second, and form the sides of a deep recess into which the base of the second metatarsal bone is received.

The first cuneiform

The first cuneiform [os cuneiforme primum] is distinguished by its large size and by the fact that when articulated, the base of the wedge is directed downward and the apex upward. The posterior surface is concave and pyriform for articulation with the medial facet on the anterior surface of the navicular. The anterior surface forms a reniform articular facet for the base of the first metatarsal. The medial surface is rough, and presents an oblique groove for the tendon of the tibialis anterior; this groove is limited inferiorly by an oval facet into which a portion of the tendon is inserted. The lateral surface is concave and presents along its superior and posterior borders a reversed L-shaped facet for articulation with the second cuneiform, and, at its anterior extremity, with the second metatarsal. Anteriorly it is rough for ligaments. The inferior surface is rough for the insertion of the peroneus longus, tibialis anterior, and (usually) the tibialis posterior. The superior surface is the narrow part of the wedge and is directed upward.

Articulations

With the navicular behind, second cuneiform and second metatarsal on its lateral side, and first metatarsal in front.

Ossification

From a single nucleus, which appears in the course of the third year.

Second cuneiform bone

The second cuneiform [os cuneiforme secundum] is placed with the broad extremity upward and the narrow end downward, and is readily recognized by its nearly square base. The posterior surface, triangular and concave, articulates with the middle facet on the anterior surface of tlie navicular. The anterior surface, also triangular, but narrower than the posterior surface, articulates with the base of the second metatarsal. The medial surface has a reversed L-shaped facet running along its superior and posterior margins for articulation with the corresponding facet on the first cuneiform, and is rough elsewhere for the attachment of ligaments. On the lateral surface near its posterior border is a vertical facet, sometimes bilobed, for the third cuneiform, and occasionally a second facet at the anterior inferior angle. The superior surface forms the square-cut base of the wedge and is rough for the attachment of ligaments. The inferior surface is sharp and rough for ligaments and a slip of the tendon of the tibialis posterior.

Articulations

With the navicular behind, second metatarsal in front, third cuneiform on the lateral side, and first cuneiform on the medial side.

Ossification

From a single nucleus, which appears in the fourth year.

The third cuneiform bone

The third cuneiform bone also placed with the broad end directed upward and the narrow end downward, is distinguished by the oblong shape of its base. Like the second cuneiform, the posterior surface presents a triangular facet for the navicular; and the anterior surface a triangular facet, longer and narrower, for the third metatarsal. The medial surface has a large facet extending along the posterior border for the second cuneiform, and along the anterior border a narrow irregular facet for the lateral side of the base of the second metatarsal. Occasionally, a small facet is present near the anterior inferior angle for the second cuneiform. The lateral surface has a large distinctive facet near its posterior superior angle for the cuboid, and at the anterior superior angle there is usually a small facet for the medial side of the base of the fourth metatarsal. The superior surface, oblong in shape, is rough for ligaments, and the inferior, forming a rounded margin, receives a slip of the tibialis posterior and gives origin to a few fibers of the flexor hallucis brevis.

Articulations

With the navicular behind, third metatarsal in front, cuboid and fourth metatarsal on the lateral side, second cuneiform and second metatarsal on the medial side.

Ossification

A single nucleus appears in the course of the first year.

The Cuboid bone

The cuboid, irregularly cubical in shape, is placed on the lateral aspect of the foot, forming a continuous line with the calcaneus and the fourth and fifth metatarsals.

Its posterior surface is somewhat quadrangular with rounded angles and presents a saddle- shaped articular surface for the calcaneus. Its lower and medial angle is somewhat prolonged backward beneath the sustentaculum tali (calcaneal process of the cuboid), an arrangement to oppose the upward or outward movement of the bone. This process occasionally terminates in a rounded facet, which plays on the head of the talus lateral to the facet for the calcaneo navicular ligament. The anterior surface is smaller and divided by a vertical ridge into two articular facets, a lateral for the base of the fifth, and a medial for the base of the fourth meta- tarsal. The superior surface is rough, non-articular, and directed obliquely upward. The inferior surface presents a prominent ridge for the attachment of the long plantar (calcaneo-cuboid) ligament, in front of which is a deep groove - the peroneal groove - running obliquely forward and medially and lodging the tendon of the peroneus longus. The ridge terminates laterally in an eminence, the tuberosity of the cuboid, on which there is usually a facet for a sesamoid bone of the tendon contained in the groove. The part of the surface behind the ridge is rough for the attachment of the plantar (short) calcaneo-cuboid ligament, a slip of the tibialis posterior, and a few fibers of the flexor hallucis brevis.

The medial surface presents, near its middle and upper part, an oval facet for articulation with the third cuneiform bone; behind this, a second facet for the navicular is frequently seen (fig. 243). Generally, the two facets are confluent and then form an elliptical surface (fig. 244). The remainder of this surface is rough for the attachment of strong inter- osseous ligaments.

The lateral surface, the smallest and narrowest of all the surfaces, presents a deep notch which leads into the peroneal groove.

Articulations

With the calcaneus behind, fourth and fifth metatarsals in front, third cuneiform and frequently the navicular on the medial side; occasionally also the talus.

Ossification

The cuboid is ossified from a single nucleus which appears about the time of birth.

View of the cuboid

Accessory tarsal elements

As in the carpus, a number of additional elements may occur in the tarsus. The most frequent of these is the os trigonum, which has already been noticed. Ne.\t in frequency is an additional first cuneiform, resulting from the ossification of the plantar half of that bone independently of the dorsal half, so that the bone is represented by a plantar and a dorsal first cuneiform. Other additional elements may occasionally occur at the upper posterior angle of the sustentaculum tali; at the anterior superior angle of the calcaneus, between that bone and the navicular; in the angle between the first cuneiform and the first and second metatarsals; and in the fibular angle between the fifth metatarsal and the cuboid (os Vesalianum).

The fibular portion of the navicular is sometimes united to the cuboid and quite separate from the rest of the navicular, the cuboid in such eases articulating with the talus. This condition suggests the recognition of the fibular portion of the navicular as a distinct accessory tarsal element, the cuboides secundarium, though it has not yet been observed as an independent bone in the human foot. 

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