Tarsal bones are a group of seven irregularly shaped bones that form the rear and midsection of the human foot. These bones provide structural support to the foot and play a crucial role in weight-bearing and locomotion.[2] The tarsal bones include the calcaneus, talus, navicular, cuboid, and three cuneiform bones (medial, intermediate, and lateral). They are arranged in a manner that contributes to the formation of the foot’s arches, ensuring stability and flexibility.
Location
The tarsal bones are located in the foot, specifically in the hindfoot and midfoot region. They connect the lower leg bones (tibia and fibula) to the metatarsals, forming the ankle and part of the foot’s structural framework.
Structure and Anatomy
The tarsal bones are seven irregularly shaped bones that form the rear and midfoot. They are arranged into two rows: the proximal and distal rows, with the navicular bone bridging the two.[3] Together, these bones contribute to the formation of the ankle joint, foot arches, and connections with the metatarsals.
Proximal Tarsal Bones
1. Calcaneus (Heel Bone)
- Shape and Size: The largest tarsal bone, forming the heel of the foot.
- Location: Located posteriorly, it lies below the talus and supports it.
- Articulations: Articulates with the talus superiorly (subtalar joint) and the cuboid anteriorly (calcaneocuboid joint).
- Notable Features:
- The sustentaculum tali: A medial bony projection supporting the talus.
- The calcaneal tuberosity: The posterior portion for Achilles tendon attachment.
2. Talus (Ankle Bone)
- Shape and Size: Second largest tarsal bone, with a rounded body for articulation with the tibia and fibula.[5]
- Location: Situated superiorly, it sits on top of the calcaneus and connects the foot to the leg.
- Articulations: Forms the ankle joint with the tibia and fibula and the subtalar joint with the calcaneus.
- Notable Features:
Intermediate Tarsal Bone
3. Navicular
- Shape and Size: A boat-shaped bone located medially.
- Location: Lies between the talus and the three cuneiform bones.
- Articulations: Articulates with the talus posteriorly and the three cuneiform bones anteriorly.
- Notable Features:
- The navicular tuberosity: A medial projection for attachment of the tibialis posterior tendon.
Distal Tarsal Bones
4. Cuboid
- Shape and Size: Cube-shaped, located on the lateral side of the foot.
- Location: Lies anterior to the calcaneus and lateral to the navicular.[7]
- Articulations: Articulates with the calcaneus posteriorly, the lateral cuneiform medially, and the fourth and fifth metatarsals anteriorly.
- Notable Features:
- The groove for the peroneus longus tendon: Located on the plantar surface.
5. Medial Cuneiform
- Shape and Size: The largest of the cuneiform bones, wedge-shaped.
- Location: Lies medially in the distal row, anterior to the navicular.
- Articulations: Articulates with the navicular posteriorly, the first and second metatarsals anteriorly, and the intermediate cuneiform laterally.
6. Intermediate Cuneiform
- Shape and Size: The smallest cuneiform bone, also wedge-shaped.
- Location: Lies between the medial and lateral cuneiform bones.
- Articulations: Articulates with the navicular posteriorly, the second metatarsal anteriorly, and the medial and lateral cuneiforms on either side.
7. Lateral Cuneiform
- Shape and Size: Wedge-shaped, slightly larger than the intermediate cuneiform.
- Location: Lies lateral to the intermediate cuneiform and medial to the cuboid.
- Articulations: Articulates with the navicular posteriorly, the third metatarsal anteriorly, and the cuboid laterally.[8]
Arrangement and Orientation
The tarsal bones are strategically arranged to form the arches of the foot:
- Longitudinal Arch: Formed by the calcaneus, talus, navicular, and first three metatarsals.
- Transverse Arch: Formed by the cuboid and cuneiform bones.
Surfaces and Features
Each tarsal bone has distinct articular and non-articular surfaces, allowing for multiple articulations and serving as attachment points for muscles, tendons, and ligaments.[1]
Vascular Supply
The tarsal bones are supplied by branches of the dorsalis pedis, posterior tibial, and peroneal arteries, with nutrient foramina allowing vascular entry.
Functions of Tarsal Bones
Support and Weight-Bearing
The tarsal bones provide structural support to the foot, allowing it to bear the body’s weight while standing, walking, or running. They distribute this weight efficiently across the foot and lower limbs.
Formation of Foot Arches
- The longitudinal arch (supported by the calcaneus, talus, navicular, and first three metatarsals) helps absorb shock and maintain balance.
- The transverse arch (formed by the cuboid and cuneiform bones) aids in foot stability and adaptation to uneven surfaces.
Articulation and Movement
The tarsal bones form various joints, such as the ankle joint (talocrural joint) and subtalar joint, enabling movements like dorsiflexion, plantarflexion, inversion, and eversion of the foot.
Force Transmission
They transfer forces generated by the lower leg muscles to the foot during activities like walking, running, and jumping, ensuring smooth locomotion.
Attachment Sites
The tarsal bones provide attachment points for numerous ligaments and tendons, such as the Achilles tendon (calcaneus), tibialis posterior, and peroneus longus.[4] These attachments contribute to foot stability and movement.
Shock Absorption
By forming the foot’s arches and distributing mechanical forces, the tarsal bones help absorb impact forces during activities like running and jumping, protecting the foot and lower limb structures.
Clinical Significance
The tarsal bones are integral to foot structure and function, making them susceptible to various conditions and injuries:
- Fractures:
- The calcaneus is prone to fractures from high-impact trauma, such as falls from heights.
- Talus fractures can result from ankle injuries, potentially disrupting blood supply and leading to avascular necrosis.
- Flatfoot (Pes Planus):
- Collapse of the longitudinal arch often involves abnormal positioning or dysfunction of tarsal bones like the navicular.[6]
- Tarsal Coalition:
- A congenital condition where two or more tarsal bones fuse, causing restricted movement and pain.
- Osteoarthritis:
- Degenerative changes in tarsal joints, especially the subtalar and midfoot joints, can result in stiffness and discomfort.
- Tarsal Tunnel Syndrome:
- Compression of the tibial nerve as it passes near the tarsal bones leads to pain, numbness, and tingling in the foot.
- Navicular Stress Fractures:
- Common in athletes, these fractures occur due to repetitive stress and can significantly impair mobility.