MANAGEMENT OF HIP DISLOCATION IN SPASTIC CEREBRAL PALSY PATIENTS

Abstract

Cerebral palsy is a non-progressive abnormality of the central nervous system resulting in an impairment of motor function. By definition, the insult to the central nervous system should occur before the age of two years but the manifestations of the condition can result in progressive musculoskeletal pathology throughout life. Cerebral palsy may also be associated with other disabilities such as speech disorders, visual disturbance, epilepsy and intellectual impairment. The orthopaedic surgeon should always bear in mind that surgery is only managing one aspect of the disorder and that objectives of treatment often differ with every patient. Hip displacement is the second most common deformity after equinus. These children have normal hips at birth but the hip displaces under the influence of abnormal muscle balance and tone. It is thought that increased tone in the hip flexors and adductors overcomes the relatively weaker extensors and abductors resulting in transfer of the center of hip rotation from the center of the femoral head to the lesser trochanter. The abnormal forces prevent the normal development of the acetabulum and proximal femoral geometry. In unaffected children the acetabulum normally deepens around a concentrically located femoral head during the first 6 years of life resulting in an acetabular index (Al) of less than 30º. In cerebral palsy the Al is commonly found to be higher than this. Conclusion and Summary 97 These acetabular deformities are thought to be due to eccentric pressure from the femoral head on the soft, cartilaginous acetabular anlage at the periphery of the developing acetabulum. The effects of abnormal tone on the proximal femur are equally detrimental. The neonate usually has a neck-shaft angle (NSA) of 140° that reduces to a mean of 120° in the adult. At birth femoral neck anteversion is about 40°and gradually reduced to about 12-15° at skeletal maturity. These changes may not occur in cerebral palsy and a persistent femoral anteversion of greater than 30° and NSA of 140°-150° is often found. The mildest manifestation of persistent anteversion is internal rotation of the lower limb. This can also prove problematic for the patient who walks as it is one of the causes of an internally rotated foot progression angle in gait. The abnormal functional pattern displayed by the patient determines the ultimate prognosis, and particularly surgical decisions. For example an extremity with pure spasticity will respond after surgical treatment in a more predictable and reliable way than will an extremity affected by spasticity and tension athetosis. In the latter, the preliminary assessment is more difficult, and the results of tendon lengthening are less reliable.