PATHOGENETIC RELEVANCE OF THE PREGNANCY HORMONE RELAXIN TO INBORN HIPINSTABILITY

The etiology of inborn hip dysplasia is unknown. In general, a multifa ctorial genesis is assumed. The influence of hormones on the developme nt of the fetal hip joint and its stability is discussed as well as me chanical influences. This study was carried out with the intention to examine the correlation between the concentration of the pregnancy hor mone relaxin and the stability of the hip joint in newborns. Both hips of 90 newborn children were examined clinically and sonographically. In 25 hips (13.9%), pathological sonograms according to the classifica tion of Graf were found. The relaxin concentration was measured in cor d blood using a heterologous radioimmunoassay. Statistical evaluation revealed an insignificant decrease of relaxin concentration with incre asing sonographic hip instability. The results indicate that hip insta bility frequently occurs with decreasing relaxin concentration. These facts contradict the earlier assumption that hip instability coincides with increased relaxin concentrations in newborns. We assume that the re is a worse preparation of the pelvis and the birth canal during pre gnancy due to the lower relaxin concentration and thus that there coul d be a higher pressure on the fetus in the perinatal phase. A decrease d relaxin concentration seems to have no direct effect on the hip join t tissue, but indirectly there is consequent rigidity of the tissue in mother and child, which can further promote the development of hip in stability.