Perthes' Disease in Children

What is it?

Perthes’ disease is an ill-understood disorder of the hip joint caused by a temporary loss of the blood supply to the part of the femur or thighbone, which moves in the hip socket of the pelvis.

Perthes’ disease often occurs in healthy, active young people and reasons for its development cannot always be explained. Sometimes it is a condition that runs in families (hereditary).

Causes

The hip joint is a ball and socket joint and has a wide range of movements in all directions. The range of movement reflects the shape of the joint surfaces, and conversely in Perthes’ the shape of the joint surfaces can come to reflect the range of movements.

The blood supply to the upper thighbone (femoral head) is temporarily cut off. This is thought to be caused by a slight change in blood clotting mechanisms. When the blood supply is first interrupted, the structure of the hip joint is not adversely affected but the bone in the femoral head dies to a variable extent.

It is when the blood supply grows back and new live bone is laid down that softening of the femoral head occurs and deformity can develop. The final outcome of Perthes’ disease is dependent substantially upon the final shape achieved of the femoral head.

Symptoms

1. Perthes’ disease is more common in boys than in girls.

2. Occasionally Perthes’ disease affects both hips: when it occurs in both sides doctors need to be careful to exclude other generalised disorders affecting other bones and joints.

3. A child may present with pain, decreased movement of their hip and limping. They may also be less physically active than normal.

4. Pain may sometimes only be experienced after activities, or it may be present for days or occasionally weeks at a time.

5. Sometimes a child will have decreased movement at their hip with stiffness. Typically the leg twists outwards better than inwards, taking their legs out to the sides (doing the splits) is limited or painful.

Diagnosis

Perthes’ disease is usually diagnosed on plain x-rays. In a minority of children who have aches and pains around the hip joint, Perthes’ disease is occasionally demonstrated using MRI (magnetic resonance imaging) or bone scans with abnormalities being shown here a little before they become obvious on the x-rays.

Guiding Principles of Treatment

There are very few certainties about Perthes’ disease, but it is generally acknowledged that if the femoral head is spherical at the time of healing of the disease and when the body is fully grown, the function of the hip will be best.

The Ice Cream Theory

A simple concept that explains much of what we know about Perthes’ disease is the ‘ice cream’ theory.

A scoop of ice cream sitting on the cone can melt if the temperature is raised (the bone softens during Perthes’ disease). If the scoop is kept on the ice cream whilst the temperature rises a little, the semi soft ice cream can be kept in the original shape and if the scoop is moved about on the ice cream it will maintain the original shape.

When the ice cream is refrozen (Perthes’ disease healing) it can be misshapen. The hip may have a limited range of movements. The ball of the femur cannot move about the socket properly and can be a source of symptoms.

Treatments

A substantial minority of children with Perthes’ disease simply have the diagnosis made and are managed by their parents with a little medical support. The younger the child (5-6 years) is at presentation, the less medical intervention they are likely to require and they will have a much better outcome. These children need to be encouraged to play normally, to swim regularly and do all the normal things children of this age do. Usually boys are below the age of seven and girls below the age of six.

Parents need to have a supply of painkiller syrup at hand at all times so the child’s experience of pain is minimised. Approximately 80% of children in this category do not need any further treatment.

Approximately two out of three of the total number of children who present with Perthes’ disease are successfully managed by programmes of range of movement exercises, supervised by Physiotherapists with regular medical check-ups to check on the progress of the disease. These children will occasionally need periods of bed rest for a few days at a time. If their symptoms are significant they can be allowed to participate in PE and sports, but can stop these activities a little earlier if symptoms develop. If they are prone to developing symptoms under these circumstances, they may need some painkillers at the time – or even beforehand, if it makes these activities easier.

In general, children with Perthes’ disease do not necessarily need to know the diagnosis when they are very young – many of the children aged five and six years of age do so well that it is better for parents to guide them along through life, enjoying it just as much as possible and indulging in all the usual activities. There is no reason to specifically limit any particular child’s activities, except in the name of safety. It is in fact harmful to artificially restrict a child’s activities on account of a condition like Perthes’ disease, as the child will tend to believe there is something very seriously wrong with them.

In children who are older, or who have greater than half the whole of the volume of the femoral head affected by the disease, there is a much greater risk of deformity being present when the disease heals. These children, despite vigorous physiotherapy and short periods in plaster, occasionally come to need an operation. The purpose of the operation is, in principle, to relieve pain and to produce a more comfortable range of movements and a rounder femoral head when the disease is fully healed.

Two types of operation are possible – Pelvic Osteotomy, where the hip socket is moved (this is like putting the scoop back on top of the ice cream – see Priciples of Treatment – “Ice Cream Theory”) or Femoral Osteotomy, where the thighbone is cut and adjusted, to provide a better range of comfortable movements.

Results

The good news is that whilst Perthes’ disease does cause significant short-term distress to both children and their parents, over a period of perhaps two to three years, approximately 80% or more have very little trouble until forty or more years of age.

Thereafter a great proportion of these patients will need hip replacements or other surgery carried out in their forties and fifties – ten to twenty years earlier than in the remainder of the population. In my own practice I have treated two patients in their thirties who had short service contracts with the Royal marine Commandos and clearly they passed the relevant medical!

Approximately 20% of children who have Perthes’ disease do have some relatively minor ongoing trouble in their teenage years, and eventually come to need corrective surgery (osteotomy) in their twenties. Only a very small proportion of such patients require hip replacements in their twenties (less than 5%).

Perthes’ disease is a poorly understood condition, but the outcome of its treatments is quite good for the vast majority of patients. Even those patients who have such a disability in early adult life are now being given much more effective treatment than before in order to minimise long-term disability.

Summary and Conclusion

As outlined previously, a relatively small proportion of children who have Perthes’ disease may need an operation in order to improve the long-term outcome.

Surgeons choose such patients on the basis of a deteriorating clinical situation, in conjunction with a critical evaluation of the x-rays, which may show risk factors predictive of a poor outcome. Surgeons therefore usually choose to operatively treat children with Perthes’ disease where the prognosis is quite poor, and where they feel they can improve the prognosis with an operation.

Unfortunately, no matter how successful any particular operation is, it is unlikely that any child with such severe Perthes’ disease will have a perfectly functioning hip, although generally a considerable improvement in function can be expected.

As a result of this, there is a very small minority of children who have had the best possible treatment for Perthes’ disease, but where the condition is so severe that a good outcome is very difficult to achieve. Such patients, in early adult life, may need hip resurfacing or hip replacement.

The Future

In recent years, some useful animal experiments have been performed in centres abroad (such experiments are not really possible in England because of the Animal Liberation Front).

One of the drugs (the biphosphonate family) that have been used in the treatment of osteoporosis in adults and in brittle bone disease in children, has been shown to dramatically alter the natural history of Perthes’ disease and avascular necrosis in laboratory rats.

It is possible, in the near future, with a carefully constructed protocol, such treatment might be tried when Perthes’ disease is detected in its very earliest stages.

Frequently Asked Questions

Q: Why are there so many different sources of information about Perthes’ disease that give different answers?

A: This is because Perthes’ disease is a condition where there are fewer certainties than in many other hip conditions in childhood. Even the greatest experts in the world have uncertainties about what to do with individual patients with Perthes’ disease.

Information sites on Perthes’ disease tend to range from those that do not recommend any active treatment to those that might give you the impression that all children need active treatment and a great proportion of children need operations. Many of these latter information sources are from centres where by attracting many of the more difficult to treat cases, it is easy to have the impression that a high proportion of children need operations.

There are therapeutic nihilists – practitioners who do not believe that any treatment in Perthes’ disease is effective and therefore that no active treatment should be offered. Whilst it is true that in at least three quarters of children who have Perthes’ disease, there is no role for surgical treatment, there is a small minority that vary as a proportion of any doctor’s practice, who will probably benefit from more active intervention, such as surgery.

Q: Why are there so many different operations?

A: Surgeons operative practice is, to an extent, dictated by who trained them, who their trainer was trained by and so on. They also tend to do operations they are familiar with and relatively few surgeons are, in general, developing new operations for any condition.

Another point to bear in mind is that in different phases of the disease, different operations can have a role. For instance, in relatively early stages of the disease, varus femoral osteotomy and Salter pelvic osteotomy have a role. In intermediate stages of the disease, triple pelvic osteotomy can have a role. In later stages of the disease in childhood, valgus femoral osteotomy can have a role.

Perthes’ disease is such a variable condition that it would be difficult to find two children in any hundred of comparable age, size, weight, disease severity and disease extent and this has confounded many experts’ efforts to standardise treatment and, indeed, to perform properly controlled trials.