Anatomical factors in the stability of the hip joint in the newborn.

Both the pathogenesis and management of congenital dislocation of the hip are controversial topics, not least because of lack of agreement on what constitute the essential pathological features. Studies of necropsy material have been rare, and even when a pathological change can be identified it is often uncertain whether it represents a primary feature of the disease or a secondary consequence. It is obviously desirable therefore to take any opportunity to examine pathological material, and preferably from as young a child as possible so that there should be the least secondary changes. For this reason there are described in this paper the findings in a child with bilateral congenital dislocation who died within a few hours of birth and in whom it might be expected that only primary features would be present. The specimen was dissected with the object of determining the essential cause of the instability and the mechanism by which stability could be restored. Particular attention was paid to the role of femoral anteversion and the orientation of the acetabulum because the significance of these features has been much disputed. This aspect of the investigation presented a problem, however, for although it was simple to measure these angles it was difficult to assess their significance. Le Damany pointed out in 1908 that when the leg is in the neutral or anatomical position the stability ofthe hip is influenced by the relationship to the sagittal plane ofboth the femoral neck and the acetabulum, so that if the former faces significantly forwards (anteversion) and the acetabulum is also inclined to the front a stable articulation may be impossible. Although he was careful to indicate that it was the relationship between these two elements which was important, it is the direction of the femoral neck that subsequently received most attention. The normal range of femoral anteversion is well known in both the mature and the immature, and ingenious techniques have been devised for its measurement in the living subject. Measurements of acetabular orientation on the other hand have been much less frequent, and the reports that are available lack agreement. Thus Lanz (1949) gave an average figure of 42 degrees ; that is, the plane of the acetabulum faces 42 degrees forward relative to the sagittal plane. Steindler (1935) also stated that 40 degrees is the normal figure but he did not disclose the source of his information. Getz (1955), working with the reconstructed pelves of Lapps, found 38 degrees to be the average. In contrast Shiino (1915) gave values much lower than these, with an average of 15 degrees in the male and 19 in the female. Studies of the immature pelvis show an even greater divergence. At the time of birth Lanz (1949) found the average to be 31 degrees and the figures of Dega (1933) ranged from 22 to 33. Laurent (1953) quoted still lower figures, between 10 and 25 degrees, and Fern#{225}ndez (1 965) gave values of between 1 1 degrees and minus 27 degrees -that is, the acetabulum was in some instances actually facing backwards. The only finding common to all these investigations is that there is apparently an increase in acetabular anteversion with increasing maturity, although even here there is not complete unanimity, for Salter (1967) stated that the acetabulum rotates furtiler backwards rather than forwards during early post-natal development. Such a diverse range of normal values makes it difficult to interpret the findings in pathological material : so for the purpose of the present investigation it was necessary to try to reconcile the apparent conflict in the puhlshed figures.