Anterior compartment syndrome (ACS) itself isn’t too rare. Most likely the location of the problem is what they were referring to. ACS is a sudden, large amount of swelling in an area where there isn’t enough room to hold all the fluid. ACS of the lower leg and forearm are most common. The thigh, buttock, arm, hand, shoulder, and foot can also be affected.
The other factor that may be considered “rare” is the fact that your daughter only had a single injury. Most cases of ACS occur after multiple injuries, burns, fractures, crush injuries, or bleeding disorders. Doctors are starting to report an increased number of cases of ACSC with contact sports with high-speed collisions such as football, ice hockey, and rugby.