Tendons are strong, fibrous cords of connective tissue that form the mechanical link between muscles and bones. In the foot and ankle, this complex network transmits powerful forces from the leg muscles to the foot bones, enabling movement and providing stability for activities like standing, walking, and running. The foot’s intricate design requires dozens of tendons to work in concert, allowing for both broad movements and fine control.
The Primary Engine: The Achilles Tendon
The largest and strongest tendon in the human body is the Achilles tendon, also known as the calcaneal tendon. This thick, rope-like structure connects the powerful calf muscles—the gastrocnemius and soleus—to the heel bone (calcaneus). Its primary function is to transmit force from the calf muscles to the foot, resulting in plantar flexion, the action of pointing the foot downward.
The Achilles tendon is the main engine for propulsion, making it possible to push off the ground during walking, running, jumping, and climbing stairs. It also acts as an energy-storing spring, stretching to absorb energy when the foot contacts the ground and then recoiling to release that energy during the push-off phase, which increases the efficiency of movement.
The tendon is composed mainly of collagen fibers, which grant it exceptional strength. Despite this strength, the Achilles tendon is prone to injury, often due to its limited blood supply and the high forces it must endure. A complete tear severely limits the ability to walk or stand effectively.
Stabilizing the Foot: Medial and Lateral Tendon Groups
The foot relies on two distinct tendon groups to manage stability and control the inward and outward rolling motions, known as inversion and eversion. The medial group, situated on the inside of the ankle, focuses on arch support, while the lateral group, on the outside, guards against ankle sprains. Together, these groups prevent excessive movement and maintain proper foot alignment during weight-bearing activities.
Posterior Tibial Tendon
The posterior tibial tendon is a major supporting structure of the foot, running along the back of the shin bone and wrapping around the inner ankle. It inserts onto multiple bones on the underside of the foot, including the navicular and cuneiforms. Its primary responsibility is to dynamically support the arch of the foot and control inversion.
This tendon acts like a sling, pulling up on the instep to maintain the medial longitudinal arch. When this tendon weakens or becomes dysfunctional, it can lead to the gradual collapse of the arch, a condition often called adult-acquired flatfoot. This causes the foot to flatten and the ankle to turn inward, progressively worsening the foot’s structure.
Peroneal/Fibular Tendons
The peroneal tendons, also known as fibular tendons, run down the outside of the lower leg and behind the outer ankle bone. This group consists of the peroneus longus and peroneus brevis. Their function is centered on providing lateral stability to the ankle and assisting with eversion, the motion of turning the sole of the foot outward.
These tendons act as dynamic stabilizers that help the foot and ankle balance on uneven surfaces. They are important for protecting against ankle sprains, which usually occur when the foot rolls inward. The peroneus longus continues under the foot to help support the arch, while the peroneus brevis attaches to the outside of the midfoot.
Lifting and Fine Movement: Anterior Tendons and Toe Control
A separate group of tendons works along the front of the foot to manage upward movement and the intricate control of the toes. These tendons are essential for the swing phase of walking, ensuring the foot clears the ground and that the toes are positioned correctly for the next step.
Anterior Tibial Tendon
The anterior tibial tendon is the most medial tendon on the front of the ankle and connects the tibialis anterior muscle to bones in the midfoot. This tendon is the strongest dorsiflexor of the foot, responsible for lifting the front of the foot upward toward the shin. This upward flexing of the foot prevents the toes from dragging or tripping during the swing phase of walking.
The tendon’s action of lifting the foot also contributes to inversion. Weakness or injury to the anterior tibial tendon can result in a condition called foot drop, where a person has difficulty controlling the lift of the forefoot.
Extensor and Flexor Tendons
The extensor tendons are located across the top of the foot and connect the muscles in the lower leg to the toes. These tendons, including the extensor hallucis longus for the big toe, are responsible for lifting and extending the toes. Because they lie close to the skin’s surface, they can be vulnerable to irritation from tight footwear.
Conversely, the flexor tendons are situated on the sole of the foot and are responsible for curling or gripping the toes. The flexor digitorum longus and flexor hallucis longus allow the toes to stabilize and grip the ground, providing fine motor control during complex movements. The combined action of the extensor and flexor tendons allows for the subtle adjustments in toe position necessary for maintaining balance and adapting to various ground conditions.