Hip deformity is one of the most common problems in children with cerebral palsy. Hip subluxation and dislocation are caused by a combination of factors, including neurological immaturity, spastic muscle imbalance, the absence of normal motion and weight bearing, and flexion-adduction contracture of the hip. Hip deformity results in significant morbidity in terms of pain, postural difficulty, interference with ambulation, and difficulty in perineal hygiene.

In many cerebral palsy, rehabilitation therapy is focused on treatments for equinus deformity of the foot that is easily detectable. Hip deformity, however, is not so readily detectable and early opportunities for proper management of hip problems is often missed. It is, therefore, necessary to prevent hip deformity by early evaluation and management of the hip.

The purposes of this study are to determine the proper measurements for hip deformity in young cerebral palsy patients, and the correlation of hip deformity with neurological involvement, ability of ambulation and severity of spasticity.

Thirty-three children with cerebral palsy(mean age: 32months, 22 males, 11 females) were evaluated by measurement of the migration index, acetabular index, central edge angle and neck shaft angle from bilateral hip APs, and 21 children of this group were additionally evaluated by measurement of the femoral anteversion angle from hip ultrasonograms.

The results are as follows:

1) Among the 66 hips, 19 hips(28.8%) were found to be subluxated and none were dislocated.

2) Thirteen hips were above 33.3% on the migration index and had a central edge angle of less than 15°, 1 hip was above 33.3% on the migration index with normal central edge angle and 5 hips had a central edge angle of less than 15° and were within the normal migration index range.

3) Among 42 hips that were evaluated by hip ultrasonograms, 33 hips(78.6%) had increased femoral anteversion angles and 12 of the 33 hips with increased femoral anteversion(36.4%) were found to be subluxated. The migration index value was significantly higher in the increased femoral anteversion group than in the normal group.

4) The incidence of hip subluxation was 50.0% for quadriplegia, 31.6% for diplegia, and 6.3% for hemiplegia. The migration index value for quadriplegia and diplegia was significantly higher than for hemiplegia. The femoral anteversion angle for quadriplegia was significantly higher than for diplegia.

5) The incidence of hip subluxation was 9.1% in independent walkers, 40.9% in dependent walkers, and 36.4% in nonwalkers. The migration index value in dependent walkers was significantly higher than in independent walkers.

6) There were 24 spastic cerebral palsy patients and 17 of the 48 hips of spastic type(35.4%) were found to be subluxated. Only 2 of 18 non spastic hips(11.1%) were found to be subluxated. The incidence of hip subluxation was 25.0% for mild, 32.1% for moderate, and 100.0% for severe spastic types. The migration index for the severe spastic type was significantly higher than for mild.

From the results of this study, we conclude that the migration index and central edge angle are highly correlated with hip subluxation, and the degree of neurological involvement, ability of ambulation and severity of spasticity influence hip deformity in young cerebral palsy patients. Therefore, the measurement of the migration index and femoral anteversion angle at regular intervals may be helpful in early detection and proper management of hip deformity in cerebral palsy.