Basics
As opposed to a strain, which is an injury to a muscle or a tendon, an ankle sprain is an injury that stretches or tears the ligaments, or fibrous bands, that support the ankle joint. The damage to the ligaments causes the joint to become inflamed, leading to swelling, pain, and sometimes bruising. In many cases, the injury also results in a temporary inability to move the ankle or to put weight on it.
Americans experience an estimated 850,000 ankle sprains each year, making it one of the most common injuries in the US.
Causes
Ankle sprains typically occur on uneven walking surfaces--while stepping off a curb, for example, or while strolling across a grassy lawn that has unexpected dips or holes. Making a misstep during an athletic event or while exercising can also lead to a sprain. An ankle can get sprained while a foot is firmly planted on the ground if the body gets twisted in a way that puts abnormal pressure on the ankle.
A sprained ankle is usually the result of an inward roll (inversion) injury. Figure 01 This injury occurs when the foot is forced to "roll in" (invert), putting abnormal pressure onto the outside edge of the foot. The pressure then stretches or tears one or more of the lateral, or outside, ligaments of the joint.
A much less common cause of a sprained ankle is an outward roll (eversion) injury. With this injury, the foot is suddenly turned outward, causing the medial, or inner ligaments of the ankle to be stretched or torn.
An eversion injury sometimes results in what is known as a high (syndesmotic) ankle sprain. This type of sprain occurs just above the ankle joint to the ligaments between the two major lower leg bones (tibia and fibula). High ankle sprains are treated in a similar manner to other sprains, but they tend to be more severe and take longer to heal.
This injury occurs when the foot “rolls in” (inverts), stretching or tearing one or more of the lateral, or outside, ligaments of the joint.
Figure 01. Inversion injury
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I'm Kristen Dore, PharmD. Welcome to PDR Health!
