Functional treatment of congenital dislocation of the hip.

A prerequisite for the development of congenital dislocation of the hip is ligamentous laxity of the hip-joint, which is demonstrable shortly after birth when the hip can be easily dislocated and reduced. This situation is described as dislocatable hip. Ligamentous laxity naturally tends to disappear, and 90% of all dislocatable hips in fact stabilize spontaneously. No dislocation develops unless an exogenous factor is involved. In infants born in breech presentation the hyperextension of the knees with the resulting increased tension in the hamstrings plays a role. During or shortly after birth, the deflexion of the hip-joint causes an increased tension in the relatively shortened iliopsoas muscle, as a result of which the hip can be dislocated in postero-superior direction. By the time the infant is two months old secondary changes (more specifically restricted abduction) become more pronounced. It may therefore be stated that contracture of the iliopsoas muscle is one of the causes, and restricted abduction a consequence of congenital dislocation of the hip. The degree of dislocation is determined by a balance between the degree of ligamentous laxity and the influence of exogenous factors. When the infant starts to stand and walk, its body weight also begins to function as a deforming exogenous factor. When dislocatable hips are not treated immediately after birth, the frequency of congenital dislocation of the hip at the age of three months amounts to 1-2 per 1000 neonates. The male:female ratio is 1:4. The secondary changes in the osseous structures of the hip-joint should always be studied three-dimensionally. Apart from conventional antero-posterior pelvic roentgenograms, CT-scans can enhance spatial insight. The secondary changes manifest themselves in an enlarged neck-shaft angle, increased femoral anteversion, an increased inclination of the acetabulum and possibly also in diminished acetabular anteversion. In view of the high radiation load involved, examination by CT-scan is not yet a routine procedure in congenital hip dislocation. Radiological examination is usually confined to an antero-posterior pelvic roentgenogram on which the acetabular angle, the neck-shaft angle and the CE-angle can be measured. These are all values projected in a frontal plane. To determine the real values the degree of acetabular and femoral torsion has to be known. With the aid of the CT-scan the torsion of the acetabulum and of the femoral neck as well as their summation - the instability index - can be measured without difficulty.(ABSTRACT TRUNCATED AT 400 WORDS)