The lower leg and its functions and role in stabilization.
Because the ground constantly has variables, human feet need to adapt to their interface with it immediately on contact. In normal function and anatomical position, the ankle joint has extension (dorsiflexion) and flexion (plantar flexion). All other movements in the ankle region are created by the foot’s dynamic joint structure.
The ankle is composed of the distal tibia, distal fibula and dome of the talus (also known as the ankle mortise or mortise joint). The foot is composed of 26 bones and 33 joints and has many intrinsic and extrinsic muscles. Although inversion and eversion are actions not of the ankle joint but of the foot, the musculature within the lower leg acts directly on the foot and needs no assistance from other muscles to create motion. Pronation and supination occur not in the foot but in its subtalar joint.
The ankle joint is constantly exposed to extreme mechanical conditions during even the simplest motion, such as gait. A hinge joint with only the ability to create flexion and extension freely in the sagittal plane, the ankle (tibiotarsal joint) controls movement of the leg relative to the foot. These movements are essential for walking on any surface, regardless of terrain. The ankle is subject to the weight of the entire body and the forces generated by the dissipation of kinetic energy when the foot makes contact with the ground.
This article focuses only on those muscles involved in flexion and extension of the ankle in the sagittal plane, when the sole of the foot is perpendicular to the axis of the leg. Many of these muscles have dual jobs, which are noted.
Dorsiflexion is the lifting of the dorsum (superior surface) of the foot toward the anterior surface of the leg. Range of motion (ROM) is zero to 20 degrees.
- Tibialis Anterior
This muscle originates from the upper two-thirds of the lateral tibia and medial surfaces of the first cuneiform and first metatarsal. It not only is the strongest dorsiflexor but also creates inversion of the foot.
- Extensor Digitorum Longus
This muscle originates from the lateral tibial condyle, most of the anterior fibular shaft, and the interosseous membrane. Its tendon passes under the musculature in the foot, splits into four individual tendons and inserts on toes 2 through 5. These tendons then split into two ends, each connecting to its relative toe at the middle phalanx and base of the distal phalanx. The extensor digitorum longus creates dorsiflexion of the foot and extension of toes 2 through 5.
- Extensor Hallucis Longus
This muscle arises from the medial two-thirds of the fibula and the interosseous membrane, passes under the musculature of the foot and inserts on the dorsum of the distal phalanx of the great toe. It creates dorsiflexion of the ankle and extension of the great toe.
- Peroneus Tertius
Considered part of the extensor digitorum longus, this muscle does not reach the toes. It arises from the distal third of the anterior fibula and the interosseous membrane and inserts at the dorsal base of the fifth metatarsal. The peroneus tertius acts predominantly in eversion of the foot but also creates dorsiflexion of the ankle.
Plantar flexion of the ankle occurs when the dorsum of the foot lengthens in line with the leg, or points downward (as in depressing the accelerator in a car). Plantar flexion angle is much greater than that of dorsiflexion; ROM is zero to 50 degrees.
This muscle originates by its medial and lateral heads on the distal posterior femur, just superior to the femoral condyles, and inserts on the posterior calcaneus via the Achilles tendon. It assists in stabilizing the knee during medial rotation.
This muscle has a broad origin from the posterior-superior tibia and fibula. It merges with the gastrocnemius to insert on the calcaneus via the Achilles tendon. The main function of the soleus is plantar flexion during gait.
This muscle originates at the lateral femoral condyle, travels medially around the tibia between the soleus and the gastrocnemius and shares with the gastrocnemius the common insertion into the calcaneus via the Achilles tendon. The plantaris assists in ankle plantar flexion and knee flexion.
- Flexor Hallucis Longus
This muscle arises from the posterior-inferior fibula and interosseous membrane. It runs along a groove on the posterior talus, posterior to the medial malleolus, behind the sustentaculum tali (the prominent projection on the calcaneus), and along the medial plantar surface of the foot and inserts on the plantar surface of the first distal phalanx. The flexor hallucis longis aids plantar flexion of the ankle and the great toe, supports the medial arch and creates inversion of the foot. It is also important in the propulsion phase of walking and provides anterior support for balancing on tiptoe. ‘
- Flexor Digitorum Longus
- Tibialis Posterior
The origin of this muscle begins at the interosseous membrane and the posterior- superior tibial and fibular shafts. It passes posterior to the medial malleolus and anterior to the sustentaculum tali. Its insertions span the cuboid, the lateral cuneiform, metatarsals 2 through 4 and, on its primary insertion, the medial tubercle of the navicular. The tibialis posterior not only is a plantar flexor but also has with the peroneus longus a conjunction that creates for the middle foot a “sling” that is crucial in supporting the lateral weight-bearing arches and helps stabilize the ankle in standing or rising on tiptoe. Lying medially to the long axis of the ankle joint, the tibialis posterior, flexor digitorum longus and flexor hallucis longus simultaneously produce adduction and supination.
- Peroneus Longus
This muscle arises from the head and superior-lateral shaft of the fibula. Its tendon travels behind the lateral malleolus and under the peroneal retinaculum (foot muscle), takes a complicated path inferior to the peroneal tubercle of the calcaneus and along the groove of the plantar cuboid (inferior) and inserts inferiorly on the medial cuneiform and base of the first metatarsal.
- Peroneus Brevis
Lying just beneath the peroneus longus, this muscle arises from the inferior-lateral fibular shaft. Its tendon passes behind the lateral malleolus, beneath the peroneal retinaculum and superior to the peroneal tubercle and inserts on the lateral tubercle of the fifth meta-tarsal. Both the peroneus longus and the peroneus brevis lie on the lateral side of the fibula and laterally to the long axis of the ankle joint, are extrinsic muscles and simultaneously produce abduction and pronation.
This muscle originates from the posterior- medial shaft. It runs posterior to the medial malleolus and sustentaculum tali and along the plantar surface of the foot and inserts on the second through the fifth distal phalanges. The flexor digitorum longus is the most powerful flexor of toes 2 through 5. It also supports the arches, inverts the foot and plantar flexes the ankle.
Our feet not only take on the difficult, demanding function of bearing body weight but also perform complex movements necessary for walking, running and jumping. Malfunction and malformation of the feet are common because many people wear “fashionable” high-heels and poorly fitted shoes or abuse their feet during athletic pursuits. Understanding the structure and function of the foot will help you help your clients avoid injury. You must take at least a few moments out of your sessions to train clients out of their shoes to teach them how to articulate the motion of their toes.
Of course, ankle flexion and extension are just two pieces of the intricate puzzle of gait. In the next article, I will describe movements of the foot and the essential strength and flexibility required to maintain the ability to walk throughout one’s lifetime.