A sprain is caused by
trauma (a fall, a twist, a blow to the body) that knocks a joint out of
position and overstretches or even ruptures supporting ligaments. Some
examples of this are when a person lands on an outstretched arm, slides
into a base, lands on the side of the foot or runs on an uneven surface.
Though the intensity
varies, pain, bruising and inflammation are common to all three
categories of sprains: mild, moderate and severe. The person may feel a
tear or pop in the joint. With a severe sprain, ligaments tear
completely or separate from the bone. This loosening impairs joint
function. A moderate sprain partially tears the ligament, producing joint
instability and some swelling. A ligament is stretched in a mild sprain,
but there is no joint loosening or instability.
The most common reason
for an ankle sprain is having had one already. The best prevention of a
second sprain is appropriate treatment of the first. Repeated sprains
can lead to ankle arthritis, a loose ankle or tendon injury.