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Legg-Perthes disease is another serious hip problem. It is an osteonecrosis of the femoral head. It involves the physis and metaphysis and we don’t know what causes it. We have a theory that there are two embarrassments to the femoral neck blood supply through the circumflex system because there have been some experiments done where they clamp the medial circumflex once and no osteonecrosis happened. Then they clamp it again and the head started to die. So they call it a "double infarct" theory. But again it is only a theory. It happens in children from 4 to 10 years. It is more common in boys than girls and 10% may be bilateral but it is never symmetrical. In other words, you will see the same involvement of both hips at the same time. If there is you have to think about things like epiphyseal dysplasias or some sort of renal osteodystrophy or rickets or something like Legg-Calve-Perthes disease.
The signs and symptoms. They will have a prolonged limp. They will have a waddle. They will have pain in the groin, thigh or knee. 90% have delayed bone age and short stature and their labs will be normal unlike kids that have renal problems.
Diagnostics. You want to get an AP and a lateral and an abduction x-ray of the hips and a left hand for bone age because 90% have delayed bone age. You want to note how delayed they are because that will impact on their prognosis. Bone scans can be helpful early. MRIs, I generally don’t get because they just confuse you. Here is an x_ray series of sort of the natural history of what happened to this kid whose femoral head collapsed. You can see this little wafer of bone used to be one of those nice balls of femoral head and it just collapsed and he has got changes down here in his metaphysis. Then it went on and it started to fragment a little bit and the body starts to resorb it and then it starts to rebuild a femoral head. It starts to lay down new bone and then he’s fully grown.
Classification is based on the amount of head involvement and we use the lateral column classification system. The more the lateral column out here is involved, the worse the prognosis. The prognosis is also worse if the onset of the disease is after the age of 6. Or the prognosis, I should say, is better if it is before the age of 6. The prognosis is better if treatment is instituted prior to the age of 8 and if there is no lateral column involvement. The prognosis here is excellent.
When we treat them, we want to reduce the pain, improve range of motion and minimize femoral head deformity. So what I do is I try to, first of all, you can see this dye here shows this flattening of the femoral head. All that is left of this femoral head is this little dark area right here. This is all cartilage and it is flattened. You can see how if you tilt the hip up, this flattened area will then become contained inside the acetabulum. So then I have to recreate that situation anatomically so I cut the femoral neck, I tip the head down into the socket and put this blade plate on so that the femoral head is entirely contained inside.
I use the analogy of taking some snow in your hands, if you put it in your hands and don’t move your hands you are going to wind up with a pancake. But if you take the snow and put it between your hands and start gently rolling your hands you’re going to wind up with a round snowball. Well, that is what I do here. I take the soft femoral head, which is injured, I put it deeply inside the cup and then I institute range of motion. If they move their hip around inside the cup.