It sounds like your daughter might have a condition called os trigonum syndrome. An extra piece of bone is present (usually at birth) in the ankle of affected individuals. It is located behind the talus bone (part of the ankle complex). It is connected to the talus by a band of fibrous tissue. When this bony bump gets separated from the main body of the talus, it is referred to as an os trigonum.
For the person who has an os trigonum, pointing the toes downward catches the os trigonum between the ankle and heel. The repetitive force downward on the os trigonum every time the foot is pointed causes the bone fragment to pull loose. As the os trigonum pulls away, the tissue connecting it to the talus is stretched or torn. The area becomes inflamed causing pain and loss of ankle motion.
This can be a very serious problem for a ballerina. Pointing the toe or rising up on the toes causes pain. Whether it’s a bone fragment that gets caught in the joint or some other soft tissue getting pinched, limited motion occurs preventing the dancer from performing movements essential to ballet.
Surgery to remove the bone can be done with an open incision or endoscopically. Endoscopic surgery involves a tiny incision (big enough to allow a scope to pass through the skin into the joint). A tiny TV camera on the end of the scope allows the surgeon to find the free-floating fragment and remove it.
This can be done without disrupting any blood vessels or nerves in the area. There are fewer complications and a faster recovery time. Most dancers are able to return to dancing without any problems after just a few weeks. If there is any other damage in the joint already present at the time of the operation, the surgery may be more extensive and the recovery longer.