The hip joint is a ball and socket joint (Figure 1). The upper end of the femur has a fragile blood supply.
Perthes’ disease is a disorder of growth of the hip in a child. It is due to an interruption of blood flow to the femoral head, which results in a temporary cessation of normal growth of the femoral head. When growth does resume, the femoral head may, in some patients, heal with permanent deformity. Osteoarthritis of the hip may then ensue early in adult life.
The cause of the interruption of blood flow to the femoral head remains unknown. Many theories and associations exist. Some of these are:
- Delayed bone age
- Abnormal blood clotting mechanisms.
As the cause of interrupted blood flow is essentially unknown, Perthes’ disease cannot be predicted or prevented. However, it is important to diagnose the condition early, as a golden opportunity to treat before the femoral head becomes deformed may otherwise be missed.
- Perthes’ typically occurs from 4 – 10 years of age.
- It is more common in boys. Both hips may be affected, but this is not common.
- There is a slow onset of intermittent hip, knee or thigh pain.
- The patient walks with a limp.
- The thigh muscles are wasted.
- Some movements of the hip are restricted.
- The child is otherwise well.
- Early: There is widening of the “joint space” and the femoral head appears smaller and to be more dense. These changes may be subtle and are frequently missed.
- Later: There is fragmentation of femoral head (Figure 2).
- Blood tests are all normal.
- In South Africa, TB of the hip is an important differential diagnosis. TB can have a similar clinical presentation and radiological appearance. Blood investigations are useful to distinguish the two. Sometimes a synovial biopsy is necessary.
The starting point of treatment of Perthes’ disease is to identify those hips that are at risk of healing with deformity of the femoral head. This is a clinical and x-ray assessment and requires referral to an orthopaedic surgeon familiar with the disease. The aim is to prevent the femoral head from becoming deformed during the healing process, which may take months.
- Many cases of Perthes’ disease require nothing more than observation and symptomatic treatment. This involves the use of anti-inflammatory medication, physiotherapy and occasional bed rest. Regular x-rays are taken to monitor the healing process.
- In patients where there are signs that the femoral head is at risk of becoming deformed, more active treatment may be required. In these patients bracing, casting or surgery may be advised. The principle is to improve the forces acting on the femoral head by “containing” the femoral head in the acetabulum.
- If the patient presents late and the femoral head is already deformed, it is too late for any intervention to reshape the femoral head. Other procedures could be considered to improve function or pain.
In terms of developing femoral head deformity:
- Younger children have a better prognosis.
- Girls tend to have a worse prognosis than boys.
- The amount of the femoral head involved is important.
In terms of developing osteoarthritis later in life:
- This depends on the shape of the femoral head once the healing process is complete – the more severe any residual deformity, the worse the prognosis (Figure 3).
- The majority of patients will function well and have a pain free hip for many years after initial healing.
Figure 1. Normal hip joint in a child showing a well formed ball (femoral head) and socket (acetabulum). Note the well rounded shape and uniform density of the femoral head.
Figure 2. Perthes’ disease. Note the widened joint space and dense, fragmented femoral head.
Figure 3. A femoral head that has healed with deformity.