The percentage of migration as indicator of femoral head position.

In childhood subluxation of one or both hips may develop rather insidiously. For lack of generally accepted objective methods of assessment, ambiguous interpretations of findings in serial examinations are common. Many subluxations are overlooked during the early stages. In order to overcome such disadvantages, determination of the percentage of migration seems to be a reasonably easy and reliable technique facilitating evaluation of impending dislocation. This investigation was carried out in order to establish norms applicable to patients in the pediatric age interval. The 98th percentile of migration increases with age from 16 per cent in patients less than 4 years of age to 24 per cent in patients greater than or equal to 12 years. Higher figures represent subluxation. If the migration exceeds 80 per cent a manifest luxation is present. A difference in migration between the two hips larger than 12 per cent indicates abnormality calling for clinical and radiologic follow-up.