The Ankle & Foot - Bones
What is the ankle joint?
The ankle joint (or talocrural joint) is a synovial joint located in the lower limb.
It is formed by the bones of the leg (tibia and fibula) and the foot (talus).
Functionally, it is a hinge type joint, permitting dorsiflexion and plantarflexion of the foot.
Where is the tibia?
The distal end of the tibia widens to assist with weight-bearing.
The medial malleolus is a bony projection continuing inferiorly on the medial aspect of the tibia. It articulates with the tarsal bones to form part of the ankle joint. On the posterior surface of the tibia, there is a groove through which the tendon of tibialis posterior passes.
Laterally is the fibular notch, where the fibula is bound to the tibia – forming the tibiofibular joint.
Where is the fibula?
Distally, the lateral surface of the fibula continues inferiorly, and is called the lateral malleolus.
The lateral malleolus is more prominent than the medial malleolus, and can be palpated at the ankle on the lateral side of the leg.
Understanding the bones of the foot
The bones of the foot provide mechanical support for the soft tissues; helping the foot withstand the weight of the body whilst standing and in motion.
They can be divided into three groups:
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A set of seven irregularly shaped bones. They are situated proximally in the foot in the ankle area.
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Connect the phalanges to the tarsals. There are five in number – one for each digit.
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The bones of the toes. Each toe has three phalanges – proximal, intermediate and distal (except the big toe, which only has two phalanges).
The foot can also be divided up into three regions:
Hindfoot – talus and calcaneus
Midfoot – navicular, cuboid and cuneiforms
Forefoot – metatarsals and phalanges.
Where are the tarsal bones?
The tarsal bones of the foot are organised into three rows; proximal, intermediate and distal.
The proximal tarsal bones are the talus and the calcaneus. These comprise the hindfoot, forming the bony framework around the proximal ankle and heel.
What is the talus?
The talus is the most superior of the tarsal bones. It transmits the weight of the entire body to the foot.
The main function of the talus is to transmit forces from the tibia to the heel bone (known as the calcaneus). It is wider anteriorly compared to posteriorly which provides additional stability to the ankle.
It has three articulations:
Superiorly – ankle joint – between the talus and the bones of the leg (the tibia and fibula).
Inferiorly – subtalar joint – between the talus and calcaneus.
Anteriorly – talonavicular joint – between the talus and the navicular.
Whilst numerous ligaments attach to the talus, no muscles originate from or insert onto it. This means there is a high risk of avascular necrosis as the vascular supply is dependent on fascial structures
The subtalar joint is an articulation between two of the tarsal bones in the foot – the talus and calcaneus. The joint is classed structurally as a synovial joint, and functionally as a plane synovial joint.
What is the calcaneus?
The calcaneus is the largest tarsal bone and lies underneath the talus where it constitutes the heel. It has two articulations:
Superiorly – subtalar (talocalcaneal) joint – between the calcaneus and the talus.
Anteriorly – calcaneocuboid joint – between the calcaneus and the cuboid.
It protrudes posteriorly and takes the weight of the body as the heel hits the ground when walking. The posterior aspect of the calcaneus is marked by calcaneal tuberosity, to which the Achilles’ tendon attaches.
What is the navicular?
The intermediate row of tarsal bones contains one bone — the navicular (given its name because it is shaped like a boat).
Positioned medially, it articulates with the talus posteriorly, all three cuneiform bones anteriorly, and the cuboid bone laterally. On the plantar surface of the navicular, there is a tuberosity for the attachment of part of the tibialis posterior tendon.
In the distal row, there are four tarsal bones – the cuboid and the three cuneiforms. These bones articulate with the metatarsals of the foot.
What is the cuboid?
The cuboid is furthest lateral, lying anterior to the calcaneus and behind the fourth and fifth metatarsals.
As its name suggests, it is cuboidal in shape.
The inferior (plantar) surface of the cuboid is marked by a groove for the tendon of fibularis longus.
What are cuneiforms?
The three cuneiforms (lateral, intermediate (or middle) and medial) are wedge shaped bones. They articulate with the navicular posteriorly, and the metatarsals anteriorly. The shape of the bones helps form a transverse arch across the foot. They are also the attachment point for several muscles:
Medial cuneiform – tibialis anterior, (part of) tibialis posterior and fibularis longus
Lateral cuneiform – flexor hallucis brevis
Where are the metatarsals?
The metatarsals are located in the forefoot, between the tarsals and phalanges.
They are numbered I-V (medial to lateral).
Each metatarsal has a similar structure — they are convex dorsally and consist of a head, neck, shaft and base (distal to proximal).
They have three or four articulations:
Proximally – tarsometatarsal joints – between the metatarsal bases and the tarsal bones.
Laterally – intermetatarsal joint(s) – between the metatarsal and the adjacent metatarsals.
Distally – metatarsophalangeal joint – between the metatarsal head and the proximal phalanx.
Where are the phalanges?
The phalanges are the bones of the toes.
The second to fifth toes all have proximal, middle and distal phalanges.
The great toe has only 2; proximal and distal phalanges.
They are similar in structure to the metatarsals, each phalanx consists of a base, shaft and head.
What are the bursae?
There are two main bursae around the foot and ankle joints. They are located just superior to the insertion of the Achilles (calcaneal) tendon.
Anterior or deep to the tendon is the retrocalcaneal (subtendinous) bursa, which is located between the Achilles tendon and the calcaneus.
Posterior or superficial to the Achilles tendon is the subcutaneous calcaneal bursa, also called the Achilles bursa. This bursa is located between the skin and posterior aspect of the distal Achilles tendon.
The subcutaneous medial malleolar bursa is located between the skin and the medial malleolus.
The subcutaneous bursa of lateral malleolus is rare. It is located between the skin and the lateral malleolus.
What are the accessory ossicles?
Accessory ossicles are well-corticated bony structures found close to bones or a joint. They result from unfused ossification centres and are frequently congenital.
Accessory ossicles of the feet are common developmental variants with almost 40 having been described. Knowledge of their presence is helpful so that they are not misdiagnosed as fractures
