My 14-year old daughter injured herself in a dismount from the balance beam in gymnastics. They think she'll need surgery to repair a torn ACL, but they say she isn't "skeletally mature" yet. How can they tell this?

X-ray is the number one tool for determining skeletal maturity. In children and some teens, there are growth plates (physes) at the ends of bones that aren't fused
solid yet. This allows for bone growth and expansion. The physes are visible on X-ray as dark areas called radiolucency.

In the knee, the physes of the tibial tubercle is the last physis of the knee to fuse. The tibial tubercle is the large bump on the front of the knee, just below the kneecap. Age, height, hair growth, and other signs of sexual development are also part of the picture.

Children who are close to the same height (or taller) than the tallest family member may be close to full bone growth. Also, the smaller the openings between the physes and the main bone (on X-ray), the closer the child is to full maturity.