The ankle is vulnerable to sprains because of its location and limited movements. The ligaments support the ankle by forming a strong attachment between the bones of the leg and the bones within the ankle. An ankle sprain is the sudden stretching or tearing of these ligaments supporting the ankle. Ankle sprains occur when activity makes an unusual or sudden demand on the ankle, such as excessive twisting and downward pressure placed on the ankle at the same time. The affected ankle is forced beyond its normal range of motion causing a stretching or tearing of ligaments that support it. The seriousness of the ankle sprain and its treatment will be determined by how fast or slow the ligaments were stretched.

The risk for an ankle sprain increases with activities like skateboarding, and vigorous exercise programs. Athletes who participate in sports like tennis, football, basketball, volleyball, soccer, and skiing are at greatest risk for ankle sprains. These activities put unusual demands on the ankle joint. Sudden changes in foot direction with high-impact landings, place great stress on the strength and physical limitations of the ankle.

The ankle joint provides the foot with very limited movement. It is seen as two bony bumps at the lower end of each leg bone. It is surrounded by three bones and held firmly together by numerous ligaments connecting the leg to the foot. These structures work together to give the foot the ability to move up and down. The primary movements of the ankle are called:

• plantarflexion (pointing the foot toward the floor)
  

• dorsiflexion (pointing the foot toward the ceiling)
  

• inversion (facing the soles of the feet toward each other)
  

• eversion (facing the soles of the feet away from each other).

Bones and Joints

Three bones come together to form the ankle joint:

• The tibia and fibula are two parallel bones of the lower leg. These bones are attached firmly to the ankle by strong tissues called ligaments. At the ends of each bone, large bumps (each called a malleolus) can be seen on the inner and outer side of the ankle joint.

• The talus is a smaller bone below the tibia and fibula which supports the bones of the foot. Strong ligaments connect each malleolus to the talus and other tarsal bones.
  

• The tarsals are the seven strong bones that support and give structure to the foot. Their structure is similar to that of the wrist bones.
  

Ligaments

Healthy ligaments are strong tissues that come together from different locations and directions to provide strong support during normal foot movement. They connect bones to each other and keep ankle movements within normal limits. The ligaments in the ankle are named for their location and their ability to prevent the ankle from twisting in awkward directions. Ligaments prevent the ankle from turning inward (inversion), outward (eversion), or sliding forward excessively.

• The anterior talofibular ligament connects the fibula to the talus. This ligament keeps the foot from turning inward or shifting too far forward..with movement
  

• The calcaneofibular ligament connects the end of the fibula to the heel bone. This ligament keeps the ankle from twisting inward turning under with movement
  

• The deltoid ligament is the strongest ligament in the foot. This ligament prevents the ankle from turning inward beyond the normal range of motion.

Muscles and Tendons

The ankle and foot are further supported by many muscles and tendons that work together to support the ankle joint during activity. They also help balance the body when standing.

• The gastrocnemius muscle is better known as the "calf muscle." This large muscle supports the foot and helps push the foot into activity.

• The soleus muscle works with the gastrocnemius muscle to provide support during movement while absorbing the impact of the foot as it lands.
  

• The Achilles tendon is the largest tendon that connects the muscles on the back of the lower leg to the heel. It helps the ankle to move up and down during activity. The "tiptoe" stance is accomplished by the calf muscles pulling on the heel through the Achilles tendon.

• The peroneal tendons on the outside of the ankle lie just behind the fibula. These tendons provide muscle power to move the foot outward.
  

• The medial tendons lie behind the medial malleolus. Their function is to support the arch while moving the foot inward and/or bending the toes down.

What is an ankle sprain?

Ankle sprains are the stretching and/or tearing of the ligaments that connect the tibia and fibula with the foot. The ligaments may be slightly torn, completely torn apart, or torn away from the bones (sometimes pulling away a small piece of bone where the ligament attaches).

The overwhelming majority of ankle sprains are inversion ankle sprains. This type of sprain stretches or tears the ligaments located on the outside of the ankle. An eversion ankle sprain stretches and injures ligaments on the inside of the ankle. This occurs when the foot turns outward from its normal position. The eversion ankle sprain is quite rare and usually takes longer to heal.

Other types of sprains produce either a "high ankle sprain" or a "low ankle sprain." The high ankle sprain damages the ligaments that connect the lower leg bones (tibia and fibula) to each other. The "low ankle sprain" damages the ligaments just below the ankle near the talus.

Classifying the ankle sprain helps to insure proper treatment. There are three grades of injury:

Grade I- (Mild): involves a stretch of the involved ligament.
Grade II- (Moderate): involves a partial tear of the ligament with part of the ligament remaining intact. The joint suffers minimal instability.
Grade III- (Severe): is a complete tear of the involved ligament. The ligament may separate completely from the bone and the joint will lose stability.

An additional factor in grading ankle sprains is a "stable" versus an "unstable" sprain. Unstable sprains require some form of supportive treatment.