This condition is often congenital and idiopathic, but it is seen in untreated bilateral congenital dislocation of the hips and muscular dystrophy. It is also seen due to the forward slipping of the 5th lumbar vertebra in spondylolisthesis.
An x-ray of the lumbar spine and hips will diagnose the cause in most cases. A muscle biopsy may be needed to diagnose muscular dystrophy.