More common in boys (around 5:1), particularly very active boys of short stature
Pathophysiology
The femoral head transiently loses its blood supply resulting in necrosis with subsequent abnormal growth
The femoral head may fracture and collapse
Subsequent remodeling occurs however the shape of the femoral head and congruence of the joint is determined by age of onset (with older children faring worse) and the amount of collapse
An incongruent joint will lead to early onset of arthritis and severe cases may require hip replacement in adolescence or early adulthood
Clinical presentation
Symptoms
Affected children present with pain and a limp
Most cases are unilateral and bilateral cases may represent an underlying skeletal dysplasia or a thrombophilia
Signs
Loss of internal rotation is usually the first clinical sign followed by loss of abduction and later on a positive Trendellenburg test from gluteal weakness
Investigations
X-ray - may be normal
MRI or bone scan can be used to identify pathology
Management
No specific treatment other than regular xray observation and avoidance of physical activity
Approximately 50% of cases do well
In some cases the femoral head becomes aspherical, flattened and widened
The lever arm of the abductor muscles is altered resulting in weakness (Trendellenburg positive)
Occasionally the femoral head may sublux (partially dislocate) requiring an osteotomy of the femur or acetabulum
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