Anterior cruciate ligament (ACL) injuries are very common in young athletes, especially in women because of structural differences in their bodies, which tend to begin when they reach puberty.

CNN: How do I protect my daughters' knees from sports injuries?

It represents a perception that such differences have some social significance-primarily because of perceived cultural differences though these are frequently associated with forms of structural differentiation.

UNESCO: Social and Human Sciences

The differences between the various economies that use the single currency can only be narrowed by making deep structural reforms.

BBC: European austerity: More pain than gain?