The important structures of the foot can be divided into
several categories. These include
- bones and joints
- ligaments and tendons
- muscles
- nerves
- blood vessels
Bones and Joints
The skeleton of the foot begins with the talus, or
ankle bone, that forms part of the ankle joint. The two
bones of the lower leg, the large tibia and the
smaller fibula, come together at the ankle joint to
form a very stable structure known as a mortise and tenon joint.
The mortise and tenon structure is well known to
carpenters and craftsmen who use this joint in the
construction of everything from furniture to large
buildings. The arrangement is very stable.
The two bones that make up the back part of the foot
(sometimes referred to as the hindfoot) are the talus and the
calcaneus, or heelbone. The talus is connected to the
calcaneus at the subtalar joint. The ankle joint
allows the foot to bend up and down. The subtalar joint allows the foot
to rock from side to side.
Just down the foot from the ankle is a set of five bones
called tarsal bones that work together as a group.
These bones are unique in the way they fit together. There
are multiple joints between the tarsal bones. When the foot
is twisted in one direction by the muscles of the foot and
leg, these bones lock together and form a very rigid
structure. When they are twisted in the opposite direction,
they become unlocked and allow the foot to conform to
whatever surface the foot is contacting.
The tarsal bones are connected to the five long bones of
the foot called the metatarsals. The two groups of
bones are fairly rigidly connected, without much movement at
the joints.
Finally, there are the bones of the toes, the
phalanges. The joints between the metatarsals and the
first phalanx is called the metatarsophalangeal joint
(MTP). These joints form the ball of the foot, and movement
in these joints is very important for a normal walking
pattern.
Not much motion occurs at the joints between the bones of
the toes. The big toe, or hallux, is the most
important toe for walking, and the first MTP joint is a
common area for problems in the foot.
Ligaments and
Tendons
Ligaments are the soft tissues that attach bones
to bones. Ligaments are very similar to tendons. The
difference is that tendons attach muscles to bones. Both of
these structures are made up of small fibers of a material
called collagen. The collagen fibers are bundled
together to form a rope-like structure. Ligaments and
tendons come in many different sizes, and like rope, are
made up of many smaller fibers. The thicker the ligament (or
tendon) the stronger the ligament (or tendon) is.
The large Achilles tendon is the most important tendon
for walking, running, and jumping. It attaches the calf
muscles to the heel bone to allow us to raise up on our
toes. The posterior tibial tendon attaches one of the
smaller muscles of the calf to the underside of the foot.
This tendon helps support the arch and allows us to turn the
foot inward. The toes have tendons attached that bend the
toes down (on the bottom of the toes) and straighten the
toes (on the top of the toes). The anterior tibial
tendon allows us to raise the foot. Two tendons run
behind the outer bump of the ankle (called the lateral
malleolus) and help turn the foot outward.
Many small ligaments hold the bones of the foot together.
Most of these ligaments form part of the joint
capsule around each of the joints of the foot. A joint
capsule is a watertight sac that forms around all joints. It
is made up of the ligaments around the joint and the soft
tissues between the ligaments that fill in the gaps and form
the sac.
Muscles
Most of the motion of the foot is caused by the stronger
muscles in the lower leg whose tendons connect in the foot.
Contraction of the muscles in the leg is the main way that
we move our feet to stand, walk, run, and jump.
There are numerous small muscles in the foot. While these
muscles are not nearly as important as the small muscles in
the hand, they do affect the way that the toes work. Damage
to some of these muscles can cause problems.
Most of the muscles of the foot are arranged in layers on the sole
of the foot (the plantar surface). There they connect
to and move the toes as well as provide padding underneath
the sole of the foot.
Nerves
The main nerve to the foot, the tibial nerve, enters the sole of the foot by
running behind the inside bump on the ankle, the medial
malleolus. This nerve supplies sensation to the toes and
sole of the foot and controls the muscles of the sole of the
foot. Several other nerves run into the foot on the outside of the
foot and down the top of the foot. These nerves primarily
provide sensation to different areas on the top and outside
edge of the foot.
Blood Vessels
The main blood supply to the foot, the posterior tibial artery, runs right beside the
nerve of the same name. Other less important arteries enter
the foot from other directions. One of these arteries is the
dorsalis pedis that runs down the top of the
foot. You can feel your pulse where this artery runs in the
middle of the top of the foot.
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