Definition
The term hip dislocation describes a condition in which the head of the femur in the baby’s hip joint no longer engages in the hip socket and has slipped out of it, so that the joint partners involved are no longer physiologically connected. This definition of a hip dislocation can be translated as “dislocated hip”, similar to that of the shoulder. In babies, hip dislocation is one of the most common congenital malpositions and is usually due to an abnormal development of the acetabulum during pregnancy (hip dysplasia in the child), which favors a slipping out of the head of the femur.
The acetabulum is not sufficiently formed, so that the femoral head has too much freedom of movement. As a result, even small movements cause it to slip out of its intended socket. Hip dislocation in babies affects girls about 5-6 times more frequently than boys.
In about 60% of the cases the hip dislocation in babies occurs unilaterally. The causes are manifold and are often based on incorrect positioning of the baby during pregnancy. Due to the frequency of hip dislocation in babies, an ultrasound examination of the hip is routinely performed in the first month of the U3 preventive examination in order to detect malpositions early. With a promptly initiated therapy, the hip luxation in the baby can be well treated and thus permanent damage can be prevented.
Causes
A hip luxation in babies is an expression of an insufficiently formed hip socket in the context of hip dysplasia in children, one of the most common congenital disorders of the musculoskeletal system. The cause of this hip dysplasia, which leads to hip luxation, is multifactorial. Initially, hereditary factors play a not unimportant role.
Especially girls whose mothers have already had a hip dislocation are at increased risk. In very rare cases, Ehlers-Danlos syndrome can be a cause of hip luxation. Another cause is a deviant course of pregnancy, since the normal formation of the joints takes place here.
Postures of the baby in the mother’s abdomen, which lead to constriction and thus hindered growth, are one of the main causes. Thus, twin pregnancies can cause forced postures, which can be the cause of a hip luxation in the baby. However, a reduced amount of amniotic fluid, e.g. due to transferred pregnancies or a malposition of the fetal kidneys, can also lead to a narrowing of the fetus.
Another cause of a hip luxation at the bottom of a hip dysplasia is a positional anomaly of the baby in the uterus. Especially a pelvic end position, in which the hip joints are strongly flexed, is often accompanied by a hip luxation in the baby, because here a strong pressure is exerted on the growing acetabular cups in the baby over a long period of time, which prevents them from taking their physiological form. Similarly, for reasons that are not yet fully understood, the risk of having a malformed hip is increased in the presence of other malpositions such as clubfoot or spinal column.
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