General features.-The talus forms the principal connecting link between the foot and the bones of the leg, and takes an important part in the formation of the ankle-joint. The somewhat rounded head, which is placed at the anterior end of the bone, the trochlear surface for the tibia on the superior aspect and the large triangular facet for the lateral malleolus on the lateral aspect can be recognized without difficulty, and enable a talus to be referred to its correct side of the body.
The talus possesses a head, a neck and a body.
The head of the talus is directed forwards and slightly downwards and medially. Its anterior surface, which is oval and convex, with its long axis directed downwards and medially, articulates with the posterior surface of the navicular bone. The inferior or plantar surface is marked by three articular areas, which are separated by indistinct ridges. Of these areas the most posterior is the largest ; oval in outline, it is gently convex and rests on the upper surface of the sustentaculum tali of the calcaneus. Anterior and lateral to this area, and usually continuous with it, a flattened articular facet rests on the anterolateral part of the dorsal surface of the calcaneus ; it is continuous in front with the navicular surface. Medial to the two calcaneal facets a part of the head of the talus is exposed on the plantar aspect of the articulated foot. This area is covered with articular cartilage and is continuous on the one hand with the calcaneal areas and on the other with the navicular area. In the recent state it lies in contact with the important plantar calcaneonavicular or `spring’ ligament).
The body of the talus is somewhat cuboidal in shape. Its superior aspect is covered by a trochlear articular surface, which articulates with the lower end of the tibia in the ankle-joint. It is convex from before backwards and gently concave from side to side, and it is important to observe that it is widest anteriorly. The lateral surface, triangular in outline, is smooth for articulation with the lateral malleolus, and is concave from above downwards. Above it is continuous with the trochlea ; below its prominent apex forms the lateral tubercle of the talus, The medial surface is covered in its upper part by a comma-shaped articular facet, which is deeper in front than behind and articulates with the medial malleolus. Below the facet the surface is rough and pitted by numerous vascular foramina. The posterior surface is rough and small in extent and is marked by an oblique groove, placed between two tubercles. The posterior tubercle, which is usually the larger, is situated on the lateral side of the groove ; the medial tubercle is less prominent and lies immediately behind the sustentaculum tali of the calcaneus (fig. 480). The inferior surface rests on the upper aspect of the calcaneus and is covered with an oval concave facet, the long axis of which runs forwards and laterally.
Particular features.-The talus is devoid of any muscular attachments, but, as it takes part, in the formation of the ankle, the talocalcaneal and the talocalcaneonavicular joints it provides attachment for numerous ligaments (figs. 568 and 569).
The long axis of the neck is inclined downwards and forwards and medially, making an angle of about 150 with the long axis of the body. This angle is smaller (130ï¿½-140ï¿½) in the newly-born child, and helps to account for the inverted position of the foot in young children. The dorsal surface of the neck gives attachment anteriorly to the dorsal talonavicular ligament and the anterior ligament of the ankle-joint; the posterior part of this surface therefore lies within the capsular ligament of the ankle-joint. The lateral aspect gives attachment to the anterior talofibular ligament, which extends downwards along the neighboring anterior border of the lateral surface. The inferior surface of the neck hives attachment to the interosseous talocalcaneal ligament, which is usually divisible into three parts.
The medial border of the trochlea is straight but its lateral border inclines medially at its posterior part, which is often broadened and flattened to form a. small elongated triangular area. It is this part of the bone which comes into contact with the inferior transverse tibiofibular ligament in dorsiflexion of the ankle-joint.
The posterior tubercle sometimes possesses a separate center of ossification and may remain connected to the body by a plate of cartilage. It is then termed the os trigonum. Its lateral aspect receives the posterior talofibular ligament, which extends upwards to the groove, or depression, between the tubercle and the posterior border of the trochlea. Its lower border gives attachment to the posterior talocalcaneal ligament. The groove. between the posterior and medial tubercles lodges the tendon of the flexor hallucis longus and is continuous below and in front with the groove on the under aspect of the sustentaculum tali. The medial tubercle gives attachment by its medial aspect to the medial talocalcaneal ligament below, and to the most posterior of the superficial fibers of the deltoid ligament above.
The roughened area below the comma-shaped articular facet on the medial surface provides attachment for the deep fibers of the deltoid ligament.
The long axis of the posterior calcaneal facet on the plantar surface of the body runs forwards and laterally at an angle of about 45 with the median plane. In about 10 per cent. of cases, a small pressure facet is found at the lateral end of the posterior wall of the sulcus tali; it is continuous with the anterolateral part of the posterior calcaneal facet.
General features.-The calcaneus is the largest and strongest of the tarsal bones ; it projects backwards beyond the bones of the leg so as to provide a useful lever for the muscles of the calf, which are inserted into its posterior aspect. It is irregularly cuboidal in shape, and its long axis is directed forwards, upwards and somewhat laterally. No difficulty will be experienced in distinguishing the small articular anterior end from the larger, roughened posterior end, nor in distinguishing the rough plantar surface from the upper surface, which bears a large oval, articular facet about its middle. Finally, the lateral surface is flattened, whereas the medial surface is hollowed out from above downwards and backwards. The student should now have no difficulty in assigning a calcaneurn to its correct side of the body.
The upper surface is subdivisible into three areas. The posterior third is roughened, convex from side to side and concave from behind forwards ; it supports a mass of fibro-fatty tissue interposed between the strong tendo calcaneus and the back of the ankle-joint. The middle third is covered by the posterior facet for the talus, which is oval in outline and convex from behind forwards and laterally, The anterior third is partly articular and partly non-articular. In front of the posterior articular facet there is a rough depression, which becomes narrower and takes the form of a groove on the medial side. This is termed the sulcus calcanei or groove of the calcaneus ; it corresponds to the sulcus tali and helps it to complete the sinus tarsi in the articulated foot. In front of and medial to this groove an elongated articular area covers the upper surface of a projecting shelf, termed the sustentaculum tali, and extends forwards and medially on to the body of the bone. This area is not infrequently subdivided into two parts by a narrow non-articular interval, which marks the anterior limit of the sustentaculum tali. They constitute the middle and anterior facets for the talus.
The plantar surface is rough and is marked by three tubercles. The lateral and medial tubercles are placed at the posterior part of this surface and are separated from each other by a slight notch. The medial tubercle is the larger of the two. Near the anterior part of this surface the anterior tubercle forms a rounded prominence, which is separated from the anterior surface by a narrow rough area.
The lateral surface is flattened and is much deeper behind than in front. Anteriorly it presents a small elevation, termed the peroneal tubercle, which is exceedingly variable in its size. When well developed, it exhibits an oblique groove on its postero-inferior aspect, for the peroneus longus tendon, and a shallower groove on its anterosuperior aspect, for the peroneus brevis tendon. About 1 cm. or more behind the peroneal tubercle a second elevation marks the bone and gives attachment to part of the lateral ligament of the ankle-joint.
Particular features.-The groove of the calcaneus gives attachment to the interosseous talocalcaneal ligament (p. 499). In addition, the non-articular area in front of the posterior facet for the talus gives partial origin to the extensor digitorum brevis and attachment to the principal hand of the inferior extensor retinaculum (cruciate ligament) and to the stem of the bifurcated ligament.
The medial tubercle gives origin by its prominent media1 margin to the abductor hallucis (fig. 481) and attachment to the superficial part of the flexor retinaculum (laciniate ligament), and in front to the plantar aponeurosis and the flexor digitorum brevis. The lateral tubercle gives origin to the abductor digiti minimi, which extends medially in front of the medial tubercle. The roughened strip between the medial and lateral tubercles, behind, and the anterior tubercle, in front, gives attachment to the long plantar ligament while the short plantar (plantar calcaneocuboid) ligament springs from the anterior tubercle and the narrow rough area between it and the anterior surface (fig. 481). The lateral tendinous head of the flexor digitorum accessories (quadratus plantae) arises from the bone in front of the lateral tubercle and adjoining the lateral margin of the long plantar ligament.
The rough posterior surface is wider below than above. Close to the medial side of the insertion of the tendocalcaneus it receives the insertion of the plantaris muscle.
The lateral surface is crossed in front by the tendons of the peroneus longus and brevis but in most of its extent is covered only by the slain and superficial fascia. The peroneus brevis tendon, after passing round the lateral malleolus, runs forwards and slightly down wards above and in front. of the peroneal tubercle ; the peroneus longus tendon passes downwards and forwards below and behind the tubercle, which gives attachment to a slip from the inferior peroneal retinaculum. The calcaneofibular ligament is attached to the bone about 1 cm. or more behind the peroneal tubercle; and the site is usually indicated by a, low rounded elevation.
The navicular bone is situated at the medial side of the tarsals and is interposed between the head of the talus behind and the cuneiform bones in front.
The anterior surface is somewhat convex from side to side and is subdivided into three facets, of which the most medial is the largest, for articulation with the three cuneiform bones. The posterior surface, oval and concave, articulates with the head of the talus. The superior surface is roughened and is convex from side to side. The medial surface is also rough and is continued downwards to form a prominent projection, termed the tuberosity. It can be felt through the skin about 2.5 cm. below and in front of the medial malleolus. The plantar surface, also roughened, is somewhat concave, and is separated from the tuberosity on the medial side by a distinct groove. The lateral surface is rough and irregular, but frequently presents a facet for articulation with the cuboid bone.
Particular features.–The facet for the medial cuneiform is triangular in outline and its rounded apex is placed on the medial side. The facets for the intermediate and lateral cuneiform bones are also triangular, but their apices lie inferiorly. The dorsal surface gives attachment to the dorsal talonavicular, cuneonavicular, and cubonavicular ligaments. The tuberosity of the navicular bone provides the principal insertion for the tibialis posterior tendon and the groove which lies on its lateral side on the plantar surface transmits the part of this tendon which runs forwards to reach the cuneiform bones and the bases of the middle three metatarsal bones.A slight projection marks the plantar surface of the bone on the lateral side of the groove. Together with the posterior eclde of this surface it gives attachment to the plantar calcaneonavicular or ‘spring’ ligament. The roughened part of the lateral surface gives attachment to the caleaneonavicular part of the bifurcated ligament.
The cuneiform bones, three in number, are wedge-shaped and articulate with the navicular bone behind and the bases of the first, second and third metatarsal bones in front. The medial cuneiform bone is the largest, and the intermediate the smallest of the three. In the intermediate and in the lateral cuneiform bone the dorsal surface forms the broad base of the wedge and the narrow plantar surface represents the thin edge, but in the medial cuneiform bone the wedge is reversed so that its thin edge is represented by the :narrow dorsal surface of the bone. This arrangement is an important factor in the constitution of the transverse arch of the foot. The posterior surfaces of the three cuneiform bones form a slight concavity for the navicular bone, but the anterior parts of the medial and lateral cuneiforms project in front of the anterior part of the intermediate cuneiform bone, and form with it a deep recess in which the base of the second metatarsal bone is lodged.
The intermediate cuneiform bone (fig. 492) is placed between the medial and the lateral cuneiform bones. It articulates in front with the base of the second metatarsal anti behind with the navicular bone. It is of very regular wedge-like form, the broad base of the wedge forming the roughened dorsal, surface, and the thin edge the narrow plantar surface, which receives a slip from the tibialis posterior tendon. The anterior and posterior surfaces are each covered with a triangular articular facet. for the base of the second metatarsal and the navicular bone, respectively. The medial surface is partly articular and partly non-articular. Its posterior and upper margins bear a F-shaped strip; occasionally subdivided into two parts, for articulation with the medial cuneiform. The lateral surface also is partly, articular and partly non-articular. Its posterior margin bears a vertical strip, usually indented at its middle, for articulation with the lateral cuneiform bone. Strong interosseous ligaments connect the non-articular parts of the lateral and medial surfaces to the lateral and medial cuneiform bones respectively.
General features.-The cuboid bone is the most lateral bone of the distal row of the tarsals, and is situated between the calcaneus behind and the fourth and fifth metatarsal bones in front.
The dorsal surface, directed laterally as well as upwards, is rough for ligamentous attachments. The plantar surface is crossed in front by an oblique groove for the peroneus longus tendon and is bounded behind by a prominent ridge, which ends laterally in an enlargement, termed the tuberosity of the cuboid bone. The lateral aspect of the tuberosity is faceted by the sesamoid bone or cartilage which is frequently found in the peroneus longus tendon. Behind the ridge the plantar surface is rough and, owing to the obliquity of the calcaneocuboid joint, extends backwards and medially so that the medial border of this surface is much longer than the lateral border. The rough lateral surface exhibits a deep notch, which marks the commencement of the groove for the peroneus longus tendon. The medial surface is much more extensive and is partly articular and partly non-articular. It is marked near its center by a smooth oval facet for articulation with the lateral cuneiform bone ; behind this a small facet for the navicular bone is sometimes present. The two form a continuous articular surface but are separated by a vertical ridge. The anterior surface is divided by a vertical ridge into two articular areas ; the medial facet is quadrilateral in form and articulates with the base of the fourth metatarsal bone ; the lateral facet, triangular in outline with the apex on the lateral side, articulates with the base of the fifth metatarsal bone. The posterior surface is smooth, triangular and concavoconvex for articulation with the anterior surface of the calcaneus ; its medial plantar angle projects backwards as a process which helps to support the anterior end of the calcaneus.
The Homologies of the Carpals and the Tarsals.-In the most primitive reptiles the carpals and tarsals resemble one another very closely and, on the assumption that the radius, which is the pre-axial bone of the forearm, is homologous with the tibia, which is the pre-axial bone of the leg- a view which is generally but not universally accepted–little difficulty is experienced in determining the homologies of their constituent elements. In man the carpals remains relatively primitive and the identification of its elements in the reptilian carpals is a comparatively simple problem. Owing to the adoption of the erect attitude the human tarsals has been modified very considerably, and it is only by reference to the primitive reptilian condition, that any clue can be obtained to the homologies of the carpal and tarsal bones.
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