The important structures of the ankle can be
divided into several categories. These include
- bones and joints
- ligaments and tendons
- muscles
- nerves
- blood vessels
The top of the foot is referred to as the
dorsal surface. The sole of the foot is the
plantar surface.
Bones and Joints
The ankle joint is formed by the connection of
three bones. The ankle bone is called the
talus. The top of the talus fits inside a
socket that is formed by the lower end of the
tibia (shinbone) and the fibula (the
small bone of the lower leg). The bottom of the talus
sits on the heelbone, called the calcaneus.
The talus works like a hinge
inside the socket to allow your foot to move up
(dorsiflexion) and down
(plantarflexion).
Woodworkers and craftsmen are familiar with the
design of the ankle joint. They use a similar
construction, called a mortise
and tenon, to create stable structures. They
routinely use it to make strong and sturdy items, such
as furniture and buildings.
Inside the joint, the bones are covered with a
slick material called articular cartilage.
Articular cartilage is the material that allows the
bones to move smoothly against one another in the
joints of the body.
The cartilage
lining is about one-quarter of an inch thick in most
joints that carry body weight, such as the ankle, hip,
or knee. It is soft enough to allow for shock
absorption but tough enough to last a lifetime, as
long as it is not injured.
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. Thickness of the ligament or
tendon determines its strength.
Ligaments on both sides of the ankle joint help
hold the bones together. Three
ligaments make up the lateral ligament
complex on the side of the ankle farthest from the
other ankle. (Lateral means further away from
the center of the body.) These include the anterior
talofibular ligament (ATFL), the
calcaneofibular ligament(CFL), and the
posterior talofibular ligament (PTFL). A thick
ligament, called the deltoid ligament, supports
the medial ankle (the side closest to your
other ankle).
Ligaments also support the lower end of the leg
where it forms a hinge for the ankle. This series of
ligaments supports the ankle syndesmosis, the
part of the ankle where the bottom end of the fibula
meets the tibia. Three
main ligaments support this area. The ligament
crossing just above the front of the ankle and
connecting the tibia to the fibula is called the
anterior inferior tibiofibular ligament
(AITFL). The posterior fibular ligaments attach
across the back of the tibia and fibula. These
ligaments include the posterior inferior
tibiofibular ligament (PITFL) and the
transverse ligament. The interosseous
ligament lies between the tibia and fibula.
(Interosseous means between bones.) The
interosseus ligament is a long sheet of connective
tissue that connects the entire length of the tibia
and fibula, from the knee to the ankle.
The ligaments that surround the ankle joint help
form part of the joint
capsule. 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.
The ankle joint is also supported by nearby
tendons. The large Achilles
tendon is the most important tendon for
walking, running, and jumping. It attaches the calf
muscles to the calcaneus (heelbone) and allows 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 anterior tibial tendon
allows us to raise the foot. Two tendons run behind
the outer bump of the ankle (the lateral
malleolus). These two tendons, called the
peroneals, help turn the foot down and out.
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Muscles
Most of the motion of the ankle is caused by the
stronger muscles in the lower leg whose tendons pass
by the ankle and connect in the foot. Contraction of
the muscles in the leg is the main way that we move
our ankle when we walk, run, and jump.
The key ankle muscles have been discussed earlier
in the section on ligaments and tendons. These muscles
and their actions are also listed here.
- The peroneals (peroneus longus and
peroneus brevis) on the outside edge of the
ankle and foot bend the ankle down and out.
- The calf muscles (gastrocnemius and
soleus) connect to the calcaneus by the
Achilles tendon. When the calf muscles tighten, they
bend the ankle down.
- The posterior tibialis muscle supports the arch
and helps turn the foot inward.
- The anterior tibialis pulls the ankle upward.
Nerves
The nerve supply of the ankle is from nerves that
pass by the ankle on their way into the foot. The
tibial
nerve runs behind the medial malleolus.
Another nerve crosses in front of the ankle on its way
to top of the foot. There is also a nerve that passes
along the outer edge of the ankle. The nerves on the
front
and outer edge of the ankle control the muscles in
this area, and they give sensation to the top and
outside edge of the foot.
Blood
Vessels
The ankle gets blood from nearby arteries that pass
by the ankle on their way to the foot. The dorsalis
pedis runs in front of the ankle to the top of the
foot. (You can feel your pulse where this artery runs
in the middle of the top of the foot.) Another large
artery, called the posterior
tibial artery, runs behind the medial
malleolus. It sends smaller blood vessels to the
inside edge of the ankle joint. Other less important
arteries
entering the foot from other directions also
supply blood to the ankle.