Anatomy of the Foot: Part 2

In part one of Anatomy of the Foot, we covered the basic structure of the foot — from the three sections and three arches, to the bones and their ligaments. In part two, we’ll get into the muscles and tendons that make the foot move.

Tendons

Like the ligaments of the foot, there are numerous tendons that attach the muscles of the lower leg to the foot. Tendons are the cord-like structures that attach muscle to bone. Here are a few key tendons along with some common forms of tendonitis.

Achilles Tendon: One of the most recognizable tendons of the body, the Achilles tendon is located at the back of the heel and attaches the calf muscles of the lower leg to the calcaneous. This tendon helps to flex the foot downward and propel you forward. Achilles tendonitis can result from overuse of the tendon while running or jumping or from a tight shoe, which can put pressure on the back of the heel.

Peroneal Tendons: There are two peroneal tendons which attach the lateral muscles of the lower leg to the foot. These tendons run underneath the lateral malleolus (the boney knob on the outer ankle) and when overused, can often times lead to peroneal tendonitis. The pain is usually felt along the lateral malleolus and heel, and can also be related to a high arch or a supinated (rolled in) foot.

Tibialis Posterior Tendon: This tendon attaches one of the deeper lower leg muscles to the foot. The tendon runs underneath the medial malleolus (the boney knob on the inner ankle) and when overused can lead to posterior tibial tendonitis. Common amongst runners or people with hyper mobile or pronated feet, pain and swelling can occur along the inner part of the ankle.

Anterior Tibial Tendon: The tendon of the anterior tibialis muscle, located in the front of the lower leg, runs over the top of the ankle to attach itself to the bottom of the inside of the foot. Pain and swelling along the top of the ankle and foot could be a sign of anterior tibialis tendonitis. This can result from excessive downhill running.

Bursa and Bursitis: Bursitis is an inflammation of the bursa sacs which lie under tendonous joints and are designed to reduce the friction against bone. One of the most common sites for bursitis on the foot is just behind your heel under the Achilles tendon. Often referred to as a “pump bump,” this bursa lies underneath the Achilles tendon and can be irritated from a tight shoe. Retrocalcaneal bursitis, as it’s called, usually develops over time and is often more acute and localized than the pain associated with Achilles tendonitis.

Muscles

Of the twenty intrinsic muscles found on the foot, only two are located on the dorsal (top) part of the foot. Seven muscles are found on the plantar (bottom) part of the foot. And the other eleven (the interosseous and lumbricals) are found between the metatarsal bones.

Dorsal foot muscles: The extensor digitorum brevis and the extensor hallucis brevis are short toe extensors. The latter extends the big toe and the former extends the other four toes.  The interosseous muscles lie between the metatarsal bones and help to move the toes from side to side and also aid in flexion and extension. There are actually two set of these interosseous muscles. The dorsal component has four muscles and the plantar component has three. Technically these muscles lie between the metatarsals, but because they’re most easily accessible from the top of the foot, they’re usually considered dorsal muscles.

Plantar foot muscles: The plantar surface of the foot is home to three layers of muscle.

First Layer: The first and most superficial layer contains three muscles. First on the list is the flexor digitorum brevis muscle which lies directly in the middle of the foot and attaches the heel to the toes. This muscles aids in flexing (curling) the four smaller toes. The abductor hallucis muscle lies along the medial longitudinal arch and helps to abduct or rather, move the big toe away from the other toes. The abductor digiti minimi muscle, found along the lateral longitudinal arch, helps to move the little toe away from the other toes. These last two toe abductor muscles are crucial in making the minor adjustments necessary to keep your balance.

Second Layer: This layer contains five muscles. The quadratus plantae muscle attaches the heel bone to the tendons of a long flexor muscle. This configuration makes it a strong aid in flexing the toes. The deeper lying lumbricals, of which there are four, lie parallel to the metatarsal bones. These tiny muscles help to flex the 2nd-5th toes.

Third Layer: This third and deepest layer has two big toe muscles and one little toe muscle. The two big two muscles are the adductor hallucis and the flexor hallucis brevis muscles. The adductor muscle moves the big toe closer to the other four toes and the flexor muscle bends the big toe downward. The last muscle in this layer, the flexor digiti minimi brevis muscle, helps to flex the little toe.

Covering all these layers of muscle are two bands of fascia that run for the heel to the ball of the foot. When irritated, it can lead to a fairly common condition called plantar fasciitis – an inflammation of the fascia.

Movements of the Foot

Finally, let’s discuss the four major planes of movement of the ankle and foot. The foot is capable of making numerous adjustments along its 33 joints, all of which are necessary for maintaining balance. For the sake of simplicity, we’ll consider the movements of the ankle joint, which move the foot.

The four major planes of movement are: dorsiflexion, plantarflexion, inversionand eversion. Each of these planes has a degree of movement that is considered part of the normal range of motion (ROM) found at the ankle.

Dorsiflexion: When you lift your foot so that your toes are pointed upward, this is called dorsiflexion. About 20 degrees of dorsiflexion is considered normal.

Plantarflexion: Flexing your foot so that your toes point downward is considered plantarflexion. Typically, 50 degrees of plantarflexion is about average.

Inversion/Supination: When your foot rolls inward so that your toes are pointed toward the midline of the body, this is referred to as a supinated or inverted foot. There tends to be more variability in this plane of movement than the previous two, so a normal range is usually between 45-60 degrees.

Eversion/Pronation: This occurs when your ankle rolls outward and your toes point away from the midline of the body. Similar to inversion, pronation of the foot falls within a normal range, which is typically 15-30 degrees. This is notably less than inversion/supination.

As one can see, there’s quite a bit to consider when discussing the feet. Hopefully this short anatomy lesson will give you some working knowledge and better equip you in making informed decisions about the care of your feet.