A coalition is a technically a connection between two bones that should not be present. Coalitions can be congenital or acquired. When acquired, it is usually due to trauma. But when the diagnosis of a coalition is given around the foot and ankle (the tarsal bones), it infers the congenital variety.
Ankle sprains are remarkably common. In fact, one can argue that it may be the most common injury in the world. The vast majority of the time someone will “twist” an ankle, have a few days to a week of discomfort, and then return to normal activity. But there are times when this is not the case.