Maximus Gage
The ankle joint is a complex structure that facilitates various movements, including inversion, eversion, plantar flexion, and dorsiflexion. Inversion of the ankle, or tilting of the foot so that the sole faces towards the body's midline, is primarily produced by two muscles: the tibialis anterior and the tibialis posterior. These muscles, along with others in the anterior and posterior compartments of the leg, play a crucial role in ankle movement and stability, contributing to the overall biomechanical performance of the ankle joint complex.
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What You'll Learn
- The tibialis anterior muscle is the strongest dorsiflexor of the foot
- The tibialis posterior muscle inverts and plantarflexes the foot
- The extensor digitorum longus is a deep-lying extrinsic muscle
- The fibularis longus is the longer and more superficial muscle
- The fibularis brevis is the deeper and shorter muscle
The tibialis anterior muscle is the strongest dorsiflexor of the foot
The tibialis anterior muscle, also known as the tibialis anticus, is the largest of four muscles in the anterior compartment of the leg. It is a lower limb muscle that arises from the myotome of the paraxial mesoderm (somites). The tibialis anterior is the strongest dorsiflexor of the foot. Dorsiflexion is critical to gait, as this movement clears the foot off the ground during the swing phase.
The tibialis anterior muscle is located alongside the lateral surface of the tibia. It originates from the lateral surface of the tibia and attaches to the medial cuneiform and the base of metatarsal I. The muscle is primarily responsible for dorsiflexion and inversion of the foot. The tibialis anterior tendon (TAT) inserts distally on the medial border of the foot. The tibialis anterior, along with the tibialis posterior, is also a primary inverter of the foot.
The tibialis anterior muscle, specifically its fleshy muscle belly, has a confluence of proximal attachments. These include the lateral condyle of the tibia, the proximal two-thirds of the lateral surface of the tibial shaft, the anterior surface of the interosseous membrane between the tibia and fibula, the deep surface of the fascia cruris, and the intermuscular septum between it and the extensor digitorum longus. The extensor digitorum longus lies laterally and deep to the tibialis anterior. Its four tendons can be palpated on the dorsal surface of the foot.
The anterior tibial artery supplies the muscle proximally. The medial tarsal arteries, which are branches of the dorsalis pedis artery, supply the tendon distally. The deep peroneal nerve, also called the deep fibular nerve, innervates the tibialis anterior muscle. The strength of the dorsiflexor muscle is frequently measured to evaluate the performance of the ankle joint in a clinical setting. Selective strengthening exercises for the tibialis anterior muscle are essential to improve the performance of the ankle joint.
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The tibialis posterior muscle inverts and plantarflexes the foot
The tibialis posterior muscle is situated in the deep posterior compartment of the lower leg. It plays a role in plantarflexing and inverting the ankle, as well as stabilising the medial longitudinal arch of the foot. Plantarflexion refers to a movement where the foot is lowered so that the sole faces posteriorly or downwards. Inversion, on the other hand, is a movement where the plantar surface of the foot tilts medially towards the midline of the body, with the lateral border of the foot pointing inferiorly.
The tibialis posterior is not to be confused with the tibialis anterior muscle, which also contributes to inverting the ankle. The tibialis anterior is the most medial muscle of the anterior compartment of the leg. It originates from the upper portion of the tibia and inserts into the medial cuneiform and first metatarsal bones of the foot. This muscle aids in any activity that requires moving the leg or keeping the leg vertical. It also helps to stabilise the ankle as the foot hits the ground during the contact phase of walking.
Dysfunction of the tibialis posterior muscle can lead to flat feet and weak arch control in adults. Therefore, strengthening this muscle can help prevent or treat conditions associated with weakness. To isolate the tibialis posterior for strengthening, individuals can start by manually assessing their muscle strength. Then, they can perform exercises that encourage plantarflexion with inversion movement.
In summary, the tibialis posterior muscle is responsible for inverting and plantarflexing the foot, and it is important for maintaining the arch of the foot. Weakness in this muscle can lead to flat feet, so strengthening the tibialis posterior can be beneficial.
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The extensor digitorum longus is a deep-lying extrinsic muscle
The extensor digitorum longus is classified as an unipennate muscle because all its muscle fibres attach to one side of the tendon. The muscle passes under the superior and inferior extensor retinaculum of the foot, and divides into four slips that run forward on the dorsum of the foot and are inserted into the second and third phalanges of the four lesser toes. The tendons to the second, third, and fourth toes are each joined by a tendon of the extensor on the lateral side. The leg portion of the muscle is supplied by two arteries: the proximal part by the anterior tibial artery and the distal part by the fibular artery. The tendons of the muscle are vascularized by the anterior lateral malleolar, lateral tarsal, metatarsal, plantar, and digital arteries.
The extensor digitorum longus is innervated by the deep fibular nerve (L5, S1), a branch of the common fibular nerve. The muscle is within the inferior extensor retinaculum, and the distal part of the muscle crosses the anterior side of the ankle joint. While traversing the retinaculum, the tendon of the extensor digitorum longus sits medially to the tendon of the fibularis tertius and laterally to the extensor hallucis longus tendon. In the dorsum of the foot, the tendons of the muscle course superficially to the extensor digitorum brevis muscle.
The extensor digitorum longus tends to be overactive and tight, compensating for an inhibited tibialis anterior. Stretching and myofascial release of the muscle, along with activation of the tibialis anterior, can help regain muscle balance and improve functional ankle dorsiflexion.
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The fibularis longus is the longer and more superficial muscle
The fibularis longus, also known as the peroneus longus, is a long muscle located in the lateral compartment of the leg. It is the longest and most superficial of the three fibularis muscles. The fibularis longus works in conjunction with the fibularis brevis to make up the lateral compartment of the lower leg. The fibularis longus is situated superficially to the fibularis brevis and is the larger of the two muscles.
The fibularis longus originates at the head and upper two-thirds of the lateral surface of the fibula, as well as the deep surface of the fascia and the connective tissue between the fibula and the muscles on the front and back of the leg. The muscle extends down the lateral compartment of the lower limb, where it transitions into a long tendon that continues into the foot. This tendon wraps around and behind the lateral malleolus of the ankle, sharing a groove with the tendon of the fibularis brevis. The groove is converted into a canal by the superior fibular retinaculum, which secures the tendons in place.
The tendon then extends forward at an angle, passing below the fibular trochlea and the tendon of the fibularis brevis, and continues underneath the cuboid bone. The cuboid groove is transformed into a canal by the long plantar ligament. Subsequently, the tendon traverses the sole of the foot at an angle and attaches to the lateral surfaces of the medial cuneiform and the first metatarsal. On rare occasions, it may also send a slip to the second metatarsal.
The fibularis longus is innervated by the superficial fibular nerve (L5, S1), which arises from the fifth lumbar and first sacral roots of the spinal cord. The main function of this muscle is to produce plantarflexion and eversion of the foot at the ankle joint. During plantarflexion, the fibularis longus, along with the fibularis brevis and the tibialis posterior, work together to extend the foot downward away from the body. In eversion, the muscle tilts the sole of the foot away from the midline of the body.
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The fibularis brevis is the deeper and shorter muscle
The fibularis brevis, also known as the peroneus brevis, is a short muscle located in the lateral part of the lower leg. It is one of three ankle everters, alongside the fibularis longus and fibularis tertius. Together, these muscles help to steady the leg upon the foot, especially when balancing on one leg. The fibularis brevis is the strongest abductor of the foot and is responsible for 63% of the power needed to evert the foot.
The fibularis brevis originates from the distal two-thirds of the lateral surface of the fibula and the adjacent part of the anterior intermuscular septum. Its muscle fibres course inferomedially along the lateral border of the fibula, forming a fusiform muscle belly. At the distal third of the leg, the fibularis brevis gives off a broad, flat tendon that passes deep to the tendon of the fibularis longus. The tendon then continues caudally, passing behind the lateral malleolus to enter the lateral part of the foot.
The tendon of the fibularis brevis inserts on the styloid process at the proximal end of the fifth metatarsal bone. This tendon is susceptible to injury, with the most common injuries being tendinopathy, dislocation, sprain, and splitting. Inversion or supination forces can cause tendon injuries to the fibularis brevis, leading to lateral ankle pain.
The fibularis brevis is supplied by the superficial fibular (peroneal) nerve. It works in conjunction with the fibularis longus and tibialis posterior to extend the foot downward away from the body at the ankle (plantar flexion). This action helps restore the foot to its anatomical position after it has been inverted.
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Frequently asked questions
The muscles that invert the ankle are the tibialis anterior, the tibialis posterior, the flexor digitorum longus, and the flexor hallucis longus.
The tibialis anterior is located in the anterior compartment of the leg, while the tibialis posterior, flexor digitorum longus, and flexor hallucis longus are located in the posterior compartment.
These muscles are responsible for inversion and plantarflexion of the foot, which is the movement of the foot downwards away from the lower leg.
