Functional Anatomy of the Feet and Ankles

The feet and ankles contain several key soft tissue structures and muscles that help dissipate gravity and ground reaction forces, each of which will be explained below. Additionally, several muscles of the feet and lower leg will be highlighted later in this section in a series of reference charts to help you better understand the functional capabilities of these important structures and how they are affected by common deviations of the feet and ankles. This essential information on functional anatomy will also help you select and design more effective corrective exercise strategies.

The Arches

The feet contain a system of arches that are made of a combination of bones, muscles, ligaments and tendons (see Figure 16). There are longitudinal arches that run along the sides of the feet from back to front which are intricately designed to help displace the weight of the body and dissipate ground reaction forces as they travel back up the body through the foot (Dimon, 2008). The foot is also arched transversely (across the foot) to enable the foot to interact softly with the ground, provide stability and mobility to the foot, and adapt to the terrain of the contact surface. The three main arches of the feet that will be discussed in this manual are:

1. the medial longitudinal arch
2. the lateral longitudinal arch
3. the transverse arch.

Figure 16: Arches of the Foot

The longitudinal arches of the foot are supported and maintained by a combination of factors. The tendons of various muscles (such as the tibialis anterior) that run below the apex of an arch help to maintain the height of the arch. The tendons of other muscles that run lengthwise along the foot (such as the peroneus longus) help provide tension in the arches. The shape and sequencing of the bones in the foot and the ligaments that hold them together provide an interlocking mechanism which provides longitudinal arch stability. The dense fascia that runs along the sole of the foot also helps support and maintain these important structures.

The medial longitudinal arch is the big arch that runs along the inside of the foot all the way from the heel to the base of the big toe. Familiar to most people, it is formed by all the bones, ligaments, tendons, muscles and fascia that lie on the medial side of the foot. This arch is one of the greatest shock absorbers in the body and helps dissipate weight and force forward and toward the midline of the body (see Figure 16) (Price & Bratcher, 2010).

Here is a brief explanation of how this arch works. When your foot comes in contact with a surface like the ground, tension is created in the medial longitudinal arch as the soft tissue structures of the medial foot elongate to help transfer weight forward over the foot. These soft tissue structures then pull the bones of the foot into an interlocked position which helps engage additional structural support for the arch. The activation of this arch helps the foot transfer weight as the body’s weight shifts from the heel toward the toes. It also enables the transfer of weight correctly to the other side of the body as a person steps forward in preparation for landing on the other foot. When the other foot makes contact with the ground, the arches in that foot activate as described above to continue the shock absorption/weight transfer cycle.

The lateral longitudinal arch lies on the outside of the foot and is made up of all the bones, ligaments, tendons, muscles and fascia that lie on the lateral side of the foot. Visually, this arch appears flatter than the medial longitudinal arch. However, it is much more solid and has less movement capabilities than the medial longitudinal arch. The lateral longitudinal arch works in conjunction with its medial counterpart to support the weight of the body (see Figure 16) (Price & Bratcher, 2010).

The transverse arch is generally considered to be the arch in the middle of the foot created by the cuneiforms and the cuboid and their supporting ligaments. However, the midfoot actually contains a series of transverse arches that run from side to side across the foot just below the start of the toes (see Figure 16). The transverse arches help with movement of the foot, dissipate shock from side to side, and provide a system of support as the foot pronates and supinates. The transverse arches are not true arches in the technical sense of the word. Rather, they are small dome-shaped structures made up of the smaller bones, ligaments, tendons, muscles and fascia that lie in the mid-front area of the foot (Dimon, 2008). The transverse arches are maintained and strengthened by ligaments, some muscles in the toes, and by muscles (whose tendons provide support as they run along the apex of the arches).

Achilles Tendon

The Achilles tendon is a very important structure in the lower leg that connects the calf muscles (gastrocnemius and soleus) to the calcaneus (heel) (see Figure 17).

Figure 17: The Achilles Tendon

The Achilles tendon helps produce a lot of energy to assist with the powerful movements required to squat, lunge, walk, jog and run (Golding & Golding, 2003). Here is how this tendon assists with movement. When a person dorsiflexes (i.e., during movements like walking, squatting, lunging, running, etc.) the lower leg (i.e., tibia and fibula) moves forward of the heel as the heel remains planted on the ground. The forward movement of the lower leg causes the Achilles tendon and soleus to lengthen which helps load the “bungee cord” system of these structures to slow down forces to both the knee and ankle joint as they bend (see Figure 18).

Figure 18: Example of the Bungee Cord Action of the

Soleus Muscle and Achilles Tendon

As the person continues walking forward, the stored energy in the structures of the lower leg helps the soleus contract (shorten) as the leg travels into extension (i.e., straightens). The gastrocnemius simultaneously lengthens as the soleus shortens to help slow down extension of the leg. The energy stored in the Achilles tendon by the elongation of both these calf muscles is used to pull the heel off the ground as the toes push downward (i.e., plantar flex) and helps propel the body forward and transfer weight over the toes for the next phase of gait. However, if the ankle does not dorsiflex correctly then functioning of the entire foot and ankle complex is affected and many painful symptoms such as Achilles tendinitis, plantar fasciitis, heel pain and impingement syndrome can result.

The Plantar Fascia

The plantar fascia is a broad band of connective tissue that runs along the bottom (i.e., plantar) surface of the foot from the heel to the base of the toes. This fascia is intertwined with the muscles present on the underside of the foot. It also connects with the fascia of the lower leg (via the Achilles tendon) and follows paths of muscles, bones, ligaments, and tendons as they travel up and around the body. These linked fascial networks are designed to help us move better as we bend, extend, side bend, and rotate. As such, disruptions in the plantar fascia can cause dysfunction, pain, and further imbalances both in the feet and ankles and elsewhere in the body. When structures of the feet and ankles are either out of alignment or not working correctly, this dysfunction often manifests in the plantar fascia in the form of pain (i.e., plantar fasciitis).

Muscles as the Slings of the Feet

The muscles of the feet and ankles work in conjunction with the arches and tendons of the foot/ankle complex to provide a range of movements – from the most delicate to the exceptionally powerful. Almost all of the muscles of the feet and ankles originate on the lower leg (or just above the knee, as in the case of the gastrocnemius) and wrap under the foot from either side or from the back (i.e., the Achilles tendon via the heel). The placement of these muscles enables them to act as slings to give the arches of the feet and the ankles support. They are extremely important in helping the body interact with contact surfaces and in assisting the body with regulating the transfer of weight forward, in rotation and from side to side.

To help you better understand how the muscles of the feet and ankles act as slings, just imagine pulling a sock on over your foot. As you pull it up your leg, the sock pulls on the underside of your foot creating tension on the sole of your foot. This pulling action gives support to the foot the entire time you are pulling up on the top of the sock. The muscles of your lower leg, feet and ankles do exactly the same job. They all wrap under and around your foot to ensure your foot has support and does not collapse under your body weight and the force of gravity (Price, 2009).