The bony structure of the foot - part II

 PART I

The tarsal bones

The posterior talus

The calcaneus

The calcaneus lies inferior to the talus and projects backwards to form the prominence of the heel, and is strongly bound to all the tarsal bones by ligaments. It is the largest bone in the foot, being oblong in shape and having six surfaces. The anterior surface faces forwards for articulation with the cuboid, being slightly convex from top to bottom and more or less flat from side to side. The medial part of this surface extends on to the medial side of the calcaneus to accommodate a backward projection of the cuboid. The posterior surface is rounded, presenting three areas. The upper part is smooth where a bursa lies between it and the tendocalcaneus. The middle, which is smooth and convex, except at its lower margin where it ends as a jagged rough edge, receives the attachment of the tendocalcaneus. The lowest part is roughened, being subcutaneous and covered by the strong fibrous tissue and fat of the heel pad. This lowest part of the posterior surface transmits the body weight from the heel to the ground and curves forwards on to the inferior surface.

Here are found the larger medial and smaller lateral tubercles projecting forwards. The inferior surface continues forwards as a rough area terminating as the anterior tubercle. The long plantar ligament attaches to the rough area. The lateral surface of the bone is slightly roughened and nearly flat. It presents two tubercles, one for the attachment of part of the lateral ligament of the ankle joint, and the other, which is slightly lower and more anterior, provides attachments for the inferior peroneal retinaculum. The latter tubercle is elongated, with a groove above and below, and is called the peroneal tubercle. The medial surface is smooth and hollowed, being overhung anteriorly by the sustentaculum tali, under which is a groove for the tendon of flexor hallucis longus. On the superior surface of the sustentaculum tali is the middle articular surface for the head of the talus. Behind the middle articular surface is a deep groove, the sulcus calcanei, which continues across the superior surface of the calcaneus in a posteromedial direction. In front of the sinus calcanei is a roughened area for the attachment of muscles and ligaments, while behind it is the posterior articular surface, convex from front to back and flat from side to side, for articulation with the under surface of the body of the talus. Behind this articular surface is a further roughened area, concave upwards from front to back and convex from side to side.

The trabecular of the calcaneus have a particular arrangement due to the weightbearing nature of the bone. From the posterior articular surface, the supporting trabeculae pass downwards and backwards to the heel and downwards and forwards to the articular area for the cuboid. Running from the heel to the anterior surface are superior and inferior arcuate systems serving to tie the bone together. Between all of these systems there is an area of less dense, and therefore weaker, bone tissue. 

The talus

The talus is situated above the calcaneus with the head and neck directed forwards and medially. It transmits the body weight from the tibia to the calcaneus and navicular. The body of the talus is wedge-shaped from front to back being wider anteriorly, and lies between the malleoli of the tibia and fibula. Its upper surface is convex from front to back and slightly concave from side to side, being pulley-shaped, and articulates with the trochlear surface of the tibia. The lateral surface of the bone is triangular in shape with its apex pointing downwards, and articulates with the medial surface of the lateral malleolus. The medial surface is partly articular, with its upper articular part being comma-shaped. The medial and lateral articular surfaces are continuous with the upper surface of the bone. Below the medial articular surface is a depressed roughened area  for attachment of the deep part of the deltoid ligament. The inferior surface of the body is also articular, being concave from front to back and articulates with the posterior facet on the upper surface of the calcaneus.

At the posterior aspect of the bone, there is a groove running downwards and medially for the tendon of flexor hallucis longus. Lateral and medial to this groove are the lateral and medial tubercles of the talus.

From the anterior and medial aspect of the body the neck projects forwards and medially. Its upper, medial and lateral surfaces are roughened, whilst its inferior surface presents an area for articulation with the calcaneus on the upper surface of the sustentaculum tali. Just behind the articular surface there is a deep groove termed the sulcus tali, which lies immediately over the sulcus calcanei and forms with it the sinus tarsi.

The head of the talus is slightly flattened anteriorly and articulates with the posterior surface of the navicular. Below this main articulation there are two smaller articular areas, one for the upper surface of the “spring” ligament and the other, which continues on to the inferior surface of the neck, for the anterior articular area of the calcaneus.

The navicular

The navicular lies anterior to the head of the talus. On its inferomedial side it presents a large tuberosity. On its inferomedial side it presents a large tuberosity. Its posterior surface is concave for articulation with the head of the talus. Its anterior surface is subdivided into three triangular areas by two faint ridges for articulation with the three cuneiform bones. The inferior surface of the bone is narrow and roughened for the attachment of ligaments and muscles. The small lateral and subcutaneous upper surfaces are rough near their edges for the attachment of interosseus ligaments, but together they form a curved surface.

The cuboid

The cuboid has six surfaces, but in reality is a cube that has been flattened from above downwards. It is situated on the outside of the lateral cuneiform bone, in front of the calcanues and behind the fourth and fifth metatarsals. Its posterior surface is slightly concave from top to bottom, but flat from side to side, articulating with the anterior surface of the calcaneus. Its medial surface is smooth on its anterior two-thirds for articulation with the lateral cuneiform and sometimes the navicular, whilst the posterior third is usually roughened for the attachment of ligaments. Anteriorly, it is nearly flat, being divided by a slight ridge into two facets for articulation with the bases of the fourth and fifth metatarsals.

The lateral surface of the cuboid is by far the smallest due to the convergence of the anterior and the posterior surfaces as they pass laterally. Nearly the entire surface is taken up by a deep groove passing downwards and forwards through which the tendon of the peroneus longus passes. The groove is continued on the under surface of the bone and crosses medially and anteriorly towards the medial cuneiform. The groove is very close to the anterior border of the bone and is limited by a prominent ridge posterior to it. The rest of the under surface of the cuboid is rough for the attachment of the long and short plantar ligaments. Its dorsal surface is roughened, and as in the case of the dorsal surfaces of the cuneiform bones and navicular, is subcutaneous.

The cuneiform bones

There are three cuneiform bones: the medial, intermediate and lateral. As their name implies they are wedge-shaped, being triangular at their anterior and posterior ends and having three rectangular surfaces along their length.

The medial cuneiform. The medial cuneiform has its apex projecting upwards and its base downwards. Its anterior and posterior surfaces are smooth for articulation with the first metatarsal and the anterior surface of the navicular respectively. Its smooth lateral surface articulates with the intermediate cuneiform in its posterior two-thirds, and the base of the second metatarsal on its anterior third. Its superior, medial and inferior surfaces form a continuous surface which forms part of the medial side of the foot. This surface is roughened by ligaments and has a smooth impression at the anteroinferior part of its medial aspect over which the tendon of tibialis anterior runs. This is the largest of the three cuneiforms.

The intermediate cuneiform. The intermediate cuneiform has its base uppermost and its apex projecting downwards. It is shorter than the other two cuneiforms and is only non-articular on its dorsal surface. It articulates medially with the medial cuneiform, laterally with the lateral cuneiform, anteriorly with the second metatarsal and posteriorly with the navicular. Part of the medial surface is roughened for the attachment of ligaments.

The lateral cuneiform. The apex of the lateral cuneiform also projects downwards with its base uppermost. The medial surface articulates mainly with the middle cuneiform having a small facet anteriorly for articulation with the second metatarsal. Its lateral surface articulates with the medial surface of the cuboid, its posterior surface with the navicular and its anterior surface with the third metatarsal. The nonarticular parts of the medial and lateral surfaces are roughened for the attachment of ligaments.

The fact that the medial cuneiform has its base projecting downwards, whilst the other two have their bases uppermost, contributes to the arch shape across the foot from medial to lateral. With the addition of the cuboid on their lateral side, the cuneiforms make up part of the transverse tarsal arch.