My four-year-old grandson has to use crutches now to keep weight off his right hip because he has something called Perthes disease. So far he has enjoyed the attention and the novelty of using crutches. But I predict this won’t last. How long will he have to use crutches to get the desired healing effect?

Treating children with Perthes hip disease presents some interesting challenges. Current approaches include non-weight-bearing (not putting any weight on the leg) for long periods of time. Age is the determining factor in the treatment of this condition. Recovery is more likely in children under the age of eight. Many children have mild Perthes disease and are able to heal and recover fully even without treatment. The hip actually remodels itself and remains smooth moving.

The primary goal of treatment for Perthes disease is to help the femoral head recover and grow to a normal shape. The closer to normal the femoral head is when growth stops, the better the hip will function in later life. The way that surgeons achieve this goal is using a concept called containment.

Containment is a simple concept. The femoral head can be molded as it heals. This is very similar to molding plastic. Plastic is poured into a molded and held in the mold as it cools. It then holds the shape of the mold. The hip socket, or acetabulum, is not affected when the femoral head loses its blood supply. It can be used as a mold to shape the femoral head as it heals.

The trick is that the femoral head must be held in the joint socket (acetabulum) as much as possible and without too much load. It is better if the hip is allowed to move and is not held completely still in the joint socket. Joint motion is necessary for nutrition of the cartilage and for healthy growth of the joint. Being non weight-bearing helps prevent further flattening and collapse of the femoral head during the healing phase.

All treatment options for Perthes disease try to position and hold the hip in the acetabulum as much as possible. The only problem is — it can take two to four years for the necrotic bone to get resorbed and replaced by new bone. And in some cases, new bone never forms. Instead, there is new granulation (healing) tissue, but that area doesn’t harden into bone, it just forms cartilage.

Many children who are diagnosed with Perthes disease do not require any treatment except careful watching. When the condition is mild, the results of not doing anything are often as good as aggressive treatment. Active treatment is advised when more than half the epiphysis is affected. Given the fact that your grandson is on crutches at such an early age, it is likely that he has more than a mild case of Perthes.

The orthopedic surgeon determines the treatment based on the child’s age and the classification of the severity of the disease. The classification is determined by the X-ray findings. Length of time in a non weight-bearing mode will probably also be determined by changes observed on repeat X-rays taken at regular intervals.