Normal Anatomy of the Foot and Ankle
The foot and ankle in the human body work together to provide balance, stability, movement and propulsion. The complex anatomy consists of:
- 26 bones
- 33 joints
- Blood vessels, nerves and soft tissues
In order to understand the conditions that affect the foot and ankle, it is important to understand the normal anatomy.
The ankle consists of three bones attached by muscles, tendons and ligaments that connect the foot to the leg. In the lower leg, there are two bones called the tibia (shinbone) and the fibula. These bones articulate with the talus or ankle bone at the tibiotalar joint (ankle joint), allowing the foot to move up and down. The bony protrusions that we can see and feel on the ankle are:
- Lateral malleolus: This is the outer ankle bone, formed by the distal end of the fibula.
- Medial malleolus: This is the inner ankle bone, formed by the distal end of the tibia.
The foot can be divided into three anatomical sections:
The hindfoot consists of the talus bone or ankle bone, and the calcaneus bone or heel bone, which is the largest bone in your foot. The calcaneus joins the talus bone at the subtalar joint, enabling the foot to rotate at the ankle. The hindfoot connects the midfoot to the ankle at the transverse tarsal joint.
The midfoot contains five tarsal bones: the navicular bone, cuboid bone and 3 cuneiform bones. It connects the forefoot to the hindfoot with muscles and ligaments. The midfoot is responsible for forming the arches of your feet and acts as a shock absorber when walking or running.
The midfoot connects to the forefoot at the five tarso metatarsal joints.
The forefoot consists of your toe bones, called phalanges, and metatarsal bones, the long bones in your feet. Phalanges connect to metatarsals at the ball of the foot by joints called metatarsophalangeal joints. Each toe has 3 phalanges and 2 joints, while the big toe contains two phalanges, two joints and two tiny round sesamoid bones that enable the toe to move up and down. Sesamoid bones are bones that develop inside of a tendon over a bony prominence.
The first metatarsal bone connected to the big toe is the thickest of the metatarsals and is the location for the attachment of several tendons. This bone is important for its role in propulsion and weight bearing.
Soft tissue anatomy
Our feet and ankle bones are held in place and supported by various soft tissues.
- Cartilage: Shiny and smooth cartilage lines ends of bones, allowing smooth movement at a joint.
- Tendons: Tendons are soft tissues that connect muscles to bones to provide support. The Achilles tendon, also called the heel cord, is the largest and strongest tendon in the body. Located at the back of the lower leg, it wraps around the calcaneus or heel bone. When inflamed, it causes a very painful condition called Achilles tendonitis and can make walking almost impossible due to the pain.
- Ligaments: Ligaments are strong rope-like tissues that connect bones to other bones and help hold tendons in place, providing stability to the joints. The plantar fascia is the longest ligament in the foot, originating at the calcaneus and continuing along the bottom surface of the foot to the forefoot. It helps support the arch of the foot and provides shock absorption. A common cause of heel pain in adults is plantar fasciitis, which can occur when repetitive micro tears occur in the plantar fascia from overuse. Ankle sprains, the most commonly reported injury to the foot and ankle area, involve ligament strains and usually occur to the talo-fibular ligament and the calcaneo-fibular ligament.
- Muscles: Muscles are fibrous tissue capable of contracting to cause body movement. There are 20 muscles, classified as intrinsic and extrinsic muscles. The intrinsic muscles are those located in the foot and are responsible for toe movement. The extrinsic muscles are located outside the foot in the lower leg. The gastrocnemius or calf muscle is the largest of these and assists with the movement of the foot. Muscle strains usually occur from overuse of the muscle, in which the muscle is stretched without proper warm up.
- Bursae: Bursae are small fluid-filled sacs that decrease friction between tendons, and bone or skin. Bursae contain special cells called synovial cells that secrete a lubricating fluid. When this fluid becomes infected, a common painful condition known as bursitis can develop.
Biomechanics of the foot and ankle
Biomechanics is a term that describes the movement of the body. The ankle joint by itself permits two movements:
- Plantar flexion: Pointing the foot downward. This movement is normally accompanied by inversion of the foot.
- Dorsiflexion: Raising the foot upward. This movement is normally accompanied by eversion of the foot.
The foot (excluding the toes) also permits two movements:
- Inversion: Turning the sole of the foot inward
- Eversion: Turning the sole of the foot outward
The toes allow four different movements:
- Plantar flexion: Bending the toes towards the sole of the foot
- Dorsiflexion: Bending the toes towards the top of the foot
- Abduction: Spreading the toes apart. This movement normally accompanies dorsiflexion.
- Adduction: Bringing the toes together. This movement normally accompanies plantar flexion.