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Foot Anatomy
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| The foot is considered to have three subdivisions: the forefoot (front part of foot, including toes), midfoot, and hindfoot (rear part of foot, including heel). The midfoot and hindfoot together are sometimes referred to as the tarsus, because they are composed of seven tarsal bones. The tarsal bones are irregular in shape and size; their interlocking shapes enable them to form a highly stable arrangement (the arches of the foot). The ankle is the joint between the tarsus and the lower leg. The bones of the forefoot, midfoot, and hindfoot are shown in Figures 13 & 14. |
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| Forefoot: |
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The framework of the forefoot is formed by five metatarsal bones, along with the phalanges (the bones of the digits or toes). Each digit has three phalanges (proximal, middle, and distal), except for the big toe, which has two (proximal and distal). The digits and their metatarsal rays are numbered from one to five, starting with the big toe.
The metatarsals and phalanges are long bones. Each has a diaphysis (shaft) with slightly flaring ends. The proximal end or base of each bone has a smooth articular surface where it forms a joint with the adjacent bone. The distal end or head also has an articular surface, except for the distal phalanges, whose distal ends provide attachment for the soft tissue (pulp) of the digit tips.
Of the metatarsal bones, the first bears the most weight and plays the most important role in propulsion; it is therefore the shortest and thickest. It provides attachment for several tendons, including tibialis anterior and peroneus longus (see below, under Muscles and tendons). The fifth metatarsal has a tuberosity (protuberance) on the lateral side of its base, to which the peroneus brevis tendon is attached. (The tuberosity of the fifth metatarsal can be felt halfway along the lateral side of the foot.) The second, third, and fourth (called the internal metatarsals) are the most stable of the metatarsals, in part because of their protected position; but also because they have only minor tendon attachments, and therefore are not subjected to strong pulling forces.
The joints between the metatarsals and the proximal phalanges are called the metatarsophalangeal (MTP) joints. Each digit also has two interphalangeal (IP) joints, proximal (PIP) and distal (DIP), except for the big toe, which has only one IP joint. Each MTP and IP joint is bound together by several ligaments,one on each side of the joint (medial and lateral collateral ligaments), and one along the plantar (sole) surface (plantar ligament).
The first MTP joint has an additional feature. Near the head of the first metatarsal, on the plantar surface of the foot, are two sesamoid bones. (A sesamoid is a small, oval-shaped bone which develops inside a tendon, where the tendon passes over a bony prominence. In this case, the tendon is that of flexor hallucis brevis, as it passes over the first metatarsal head.) These sesamoid bones articulate with the head of the first metatarsal, and function as part of the first MTP joint. They are held in place by their tendons, and are also supported by ligaments. These include the sesamoid collateral ligaments (which bind the sesamoids to the metatarsal head) and the intersesamoidal ligament (which connects the sesamoids to each other). |
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| Midfoot: |
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The midfoot is composed of five of the seven tarsal bones, the navicular, cuboid, and three cuneiform bones. These can be thought of as being arranged in two irregular rows, with the cuboid occupying space in both rows. The proximal row contains the navicular (on the medial side of the foot) and the cuboid (on the lateral side). The distal row contains the three cuneiforms (medial, intermediate, and lateral) and the cuboid (lateral to the lateral cuneiform).
The boundary between the midfoot and forefoot consists of five tarsometatarsal (TMT) joints, the joints between the distal row of the midfoot and the bases of the metatarsals. (The medial, intermediate, and lateral cuneiforms articulate with the first, second, and third metatarsals, respectively; the cuboid articulates with the fourth and fifth metatarsals.) There are also multiple joints within the midfoot itself. The distal row of the midfoot has two intercuneiform joints (between adjacent cuneiforms) and a cuneocuboid joint (between the lateral cuneiform and the cuboid). Proximally, the three cuneiforms articulate with the navicular bone (the cuneonavicular joints). In some individuals, there is also a small articulation between the cuboid and navicular.
In addition to its articular surfaces, each tarsal bone has specific features adapted for function. For example, the medial surface of the navicular projects downward to form a tuberosity, which serves as an attachment for the tibialis posterior tendon. The lateral surface of the cuboid also has a tuberosity, which serves as a ligament attachment. The cuboid bone has no major tendon attachments; however, the peroneus longus tendon passes across the cuboid tuberosity, to run in a groove on the plantar surface of the bone. The peroneus longus tendon often contains a sesamoid bone, which articulates with a small facet (articular surface) on the tuberosity. |
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| Hindfoot: |
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The remaining two tarsal bones, the talus (also called astragalus) and calcaneus, make up the hindfoot. Calcaneus is the largest tarsal bone, and forms the heel. The talus rests on top of it, and forms the pivot of the ankle.
The shape of calcaneus is complex. On its upper surface are three smooth facets, posterior, middle, and anterior, which articulate with corresponding facets on the lower surface of the talus to form the subtalar joint (Figure 12). Of these three talocalcaneal facets, the posterior is the largest, covering almost the entire width of the calcaneal body. The middle and anterior facets are located on the medial side of the upper calcaneal surface, and are usually continuous with each other. The middle and posterior facets are separated from each other by a deep groove, which together with a corresponding groove on the talus, forms a channel between the two bones called the sinus tarsi.
The lateral wall of calcaneus is nearly flat, except for a small ridge called the peroneal tubercle. The medial wall has a shelf-like projection, the sustentaculum tali. This shelf carries the middle talocalcaneal facet on its upper surface. The undersurface of the shelf has a groove for the flexor hallucis longus tendon.
The front or anterior process of calcaneus articulates with the cuboid bone to form the calcaneocuboid joint. The rear part of calcaneus consists of a large rounded projection, the calcaneal tuberosity, which forms the back of the heel and provides attachment for the Achilles tendon. The undersurface of the tuberosity forms the bottom of the heel; this surface comes into contact with the ground during weightbearing, cushioned by a fibroelastic fat pad.
The talus, which rests on top of calcaneus, also has a complex shape. The main part or body of the talus is roughly cubical. Its smooth, dome-shaped upper surface (the talar dome) articulates with the distal ends of the tibia and fibula (the two bones of the lower leg) to form the ankle joint (see The ankle, below).
The rear surface of the talar body protrudes backward to form a posterior process. In some individuals, the posterior process ossifies (develops into bone) independently, and may remain separate from the talar body as a small accessory bone called the os trigonum (see also Ossicles, below).
Projecting forward from the talar body is the head of the talus, which is separated from the body by a slight constriction called the neck. The talar head articulates with the navicular bone, forming the talonavicular joint.
The lower surface of the talus contains three smooth facets, posterior, middle, and anterior, which articulate with the corresponding facets on the upper surface of calcaneus. The posterior facet (the largest of the three) covers the undersurface of the talar body; the anterior and middle facets are located on the undersurface of the talar head. Together, these three talocalcaneal articulations form the subtalar joint.
The subtalar joint is bound together by several talocalcaneal ligaments. In addition, it is supported by portions of the medial and lateral ligaments of the ankle, which span both the ankle and the subtalar joint (see The ankle, below). The calcaneocuboid and talonavicular joints, together referred to as the midtarsal joint, form the boundary between hindfoot and midfoot. |
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| Ossicles: |
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The foot contains a variable number of ossicles or small bones. These are of two types, sesamoid bones and accessory bones. Sesamoids are small bones that develop inside a tendon, where the tendon passes over a bony prominence. The two sesamoid bones of the first MTP joint have already been mentioned; these are a constant feature. The other MTP joints only occasionally have sesamoid bones. The peroneus longus tendon frequently contains a sesamoid bone, at the point where it passes over the cuboid tuberosity. Sesamoids may also occur in other locations in the foot.
The foot may also contain ossicles that are not associated with a tendon, but result from developmental variations. In the fetus, the skeleton initially consists of cartilage, which gradually ossifies (turns to bone) during fetal development and childhood. Each bone has a primary ossification center. The process of ossification progresses outward from this center, until the bone is completely ossified. In long bones, the primary center is located in the middle of the shaft; later, secondary ossification centers develop at the ends of the long bone. Irregularly shaped bones such as the tarsal bones may also develop secondary centers. In some individuals, complete ossification does not occur; the secondary center remains separate from the rest of the bone, forming an accessory ossicle. An example is the os trigonum (mentioned earlier), which arises as a secondary ossification center in the posterior process of the talus. About 50% of individuals have an os trigonum. Accessory ossicles may also occur in other locations in the foot. |
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| Movements of the foot and toes: |
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Toe movements take place at the IP and MTP joints. These joints are capable of motion in two directions: plantar flexion (bending toward the sole of the foot) and dorsiflexion (bending toward the dorsum or top of the foot). In addition, the MTP joints permit abduction (spreading apart) and adduction (bringing together) of the toes. Abduction ordinarily accompanies dorsiflexion of the toes; adduction accompanies plantar flexion.
The foot as a whole (excluding the toes) has two movements: inversion (turning the sole inward) and eversion (turning the sole outward). All the joints of the hindfoot and midfoot, from the subtalar to the TMTs, contribute to these movements, which are complex and consist of several components. Inversion includes components of medial rotation (toeing inward) and supination (rotating the medial border of the foot upward). Eversion includes components of lateral rotation (toeing outward) and pronation (rotating the lateral border of the foot upward). In addition, foot movements ordinarily are combined with ankle movements (see The ankle, below). |
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The Foot
Information on foot structure |
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Foot Exercises
Find out which exercises to do |
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Disorders
Information on foot disorders |
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Operation Info |
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