Our daughter has had Perthes hip disease since she was six-years-old. Now at age 13, she is starting to get something called impingement. Can you help us understand what this is and why it’s developing now?

Perthes disease of the hip (also known as Legg-Calvé-Perthes) occurs when there is a loss of blood supply to the growth center at the top of the femoral head. Without enough blood, the bone dies, degenerates, and collapses.

Children with Perthes disease of the hip may recover fully without further hip problems later. The body is capable of limiting this disease and growing new bone. But in the meantime for some patients, the weight of the body on the unstable bone can cause the head of the femur to become more oval-shaped.

Children with growth disturbance of the femoral head and altered shape of the normally round femoral head (top of the thigh bone) may end up with femoroacetabular impingement (FAI) (pinching of soft tissue and bone). This problem tends to show up during adolescence (the teen years).

It takes time for changes in shape of the femoral head to occur. As the femoral head is pressed down, the femoral neck (between the shaft of the thigh bone and the femoral head) is shortened. There can be a rotation of the bone as well. All these features add to the likelihood of an impingement problem during adolescence.

X-rays will help show what’s going on. The radiologist and orthopedic surgeon look for something referred to as acetabular coverage. This is a view of how much of the femoral head is inside the socket (called the acetabulum). With impingement from Perthes, it is common to see overcoverage (shelf of the socket hangs down over too much of the femoral head).

If you haven’t seen the X-rays yet (or you saw them but didn’t understand the process), ask your surgeon for a review of your daughter’s case. This will also help you understand the proposed treatment and possible outcomes.