Etiology of Hip Displacement in Children with Cerebral Palsy

Abstract

The natural history of hip subluxation and dislocation in children with cerebral palsy shows a strong association with increasing severity of cerebral palsy best assessed with Gross Motor Function Classification System (GMFCS) grading. GMFCS IV and V have the highest risk of developing subluxation, and the highest risk is between ages 2 and 6 with reduced risk through adolescent growth. Children who have severe spasticity or are hypotonic also have higher risk. The primary cause of the hip displacement is spastic muscles causing the hip to be positioned most of the time in flexion, adduction, and internal rotation. This position with the high muscle force of spasticity causes the hip to displace in the typical posterior superior direction causing acetabular dysplasia. As the dysplasia increases, the acetabulum opens further, and the femoral head completely displaces from the hip joint. Without treatment, the hip completely dislocates and then develops progressive deformity and arthritis. This process typically causes pain with movement of the hip initially and may then leads to constant pain. The amount of pain experienced by this process is variable and maybe pain free until there is very severe destructive arthritis in hip joint.