The bones of the foot can be grouped into three categories:
1) Tarsals – the most proximal set of bones. There are seven of these.
2) Metatarsals – five bones (one for each digit), they connect the phalanges to the tarsals.
3) Phalanges – the bones of the digits.
The seven tarsal bones can be subcategorised into three further groups; proximal , intermediate and distal
The proximal group consists of the talus and the calcaneus:
Talus – The most superior of the tarsal bones, it articulates with the leg bones to form the ankle joint. It transmits the weight of the body from the tibia to the foot. This bone has no muscular attachments, and is covered in articular cartilage. It has a head, neck and body.
Calcaneus – The calcaneus lies underneath the talus as the bone of the heel. It is thick and sturdy, acting to transmit forces from the body to the ground. In addition to the talus, it also articulates with the cuboid bone anteriorly.
Clinical Relevance: Fractures of the Talus and Calcaneus
A fracture can occur to the neck of the talus, or the body:
- Neck fractures usually occur during excessive dorsiflexion of the foot, with the neck pushed into the tibia.
- Body fractures usually occur from jumping from a height.
In a talar fracture, the two malleoli of the leg bones act to hold the fragments together, so there is little displacement.
The blood supply to the talus is susceptible to damage, thus a fracture such as this requires urgent attention to prevent avascular necrosis.
As this is the bone that transmits the weight of the body to the ground, it is not surprising that the calcaneus is most commonly fractured by jumping from a height. The talus is usually driven into the bone, crushing it. Upon radiographic appearance, the calcaneus. appears shorter and fatter
The intermediate bone is the navicular, given its name because it is shaped like a boat. It articulates with the talus posterioly, the cuneiform bones anteriorly, and the cubiod laterally.
On the plantar surface of the navicular, there is a tuberosity for the attachment of the tibialis posterior tendon.
There are four remaining distal bones:
Cuboid – The most lateral bone in the distal group. The fibularis longus muscle attaches here.
Three cuneiforms – Three wedge shaped bones, called lateral, intermediate and medial. They articulate with the navicular posterioly, and the metatarsals anteriorly.
The metatarsals are numbered I-V, medially to laterally. Metatarsal I is metatarsal of the great toe and is the shortest and widest.
They have three or four articulations:
- Proximal – The bases articulate with the cuneiforms and cuboid
- Lateral – The sides of the metatarsals articulate the adjacent metatarsals
- Distal – The metatarsal heads articulate with the phalanges.
Clinical Relevance: Fractures of the Metatarsal Bones
One common mechanism of metatarsal fracture is via a blow to the foot – usually when a heavy object drops onto the foot.
The other common injury to metatarsals is a stress fracture, an incomplete fracture caused by repeated stress to the bone. It is common in athletes and occurs most frequently to metatarsals II, III and IV.
The final method of fracture is excessive inversion of the foot. If the foot is violently inverted, the fibularis brevis muscle can pull off the base of metatarsal V.
The great toe has a proximal and distal phalanx, which the other toes also have an intermediate phalanx. This makes 14 in total.