Ankle sprains are the most common injury to the soft tissue in the body. Most people turn the ankle inward and sprain the lateral ligament. This is called an inversion injury. After such an injury, almost half of all patients continue to suffer minor problems. Patients often report there is a sensation that the ankle is going to give way.

Since so many people are affected by this injury, physiotherapists are trying to find out if there is muscle weakness causing ankle sprains. From other studies, we know that the muscles on either side of the ankle are in balance with each other in the normal ankle.

A study to measure the strength of these muscles was done in Australia. A special machine was used to measure muscle contractions around the ankle. Sixteen men and women with a sprain of one ankle were included.

Researchers were able to compare the injured side to the noninjured side in this group. Earlier studies showed that there is no major difference in muscle strength from side to side in the ankle. The authors of this study reported that weakness of the muscles that twist the ankle out (evertors) doesn't seem to affect the ankle.

Weakness of the muscles that turn the ankle in (invertors) are believed to lead to ankle sprains. This is the opposite of what therapists have always thought about ankle sprains. In the past, weakness of the evertors has been blamed for inversion sprains.

Researchers think that muscle weakness of the invertors, combined with the body weight shifting over the ankle, may be the real issue. The ankle invertors can't hold the foot down as the body weight shifts over the foot. The arch lifts up and the foot is forced inward, resulting in injury. The authors of this study suggest exercises to strengthen the invertors.