Developmental dysplasia of the hip is a gradually progressing disorder reflecting anatomically different situations reaching from mild subluxation of the femoral head to full luxation of the hip. The disorder is caused by malformations of anatomic structures that have developed during the embryologic period. The pathology of developmental dislocation of the hip is associated with a loose hyperelastic capsule, elongated ligamentum teres and slight eversion of the hypertrophied acetabular rim. While the femoral head is normal in shape, excessive femoral and acetabular antetorsion may be present causing anatomic instability of the hip joint [1
Subluxation and luxation are conditions that always lead to symptomatic degenerative hip disease [5
]. Depending on the severity of dysplasia pain onset is observed already in the second decade for severely subluxed hips while minor subluxation leads to pain starting in the fifth or sixth decades. Considering this time course of disease early treatment regimens for developmental dysplasia of the hip were recommended.
While dislocated hips after birth present clinical features as the Ortolani's and Barlow's sign [8
], subluxated hips present significant changes in the sonographic morphology of the hip. Therefore, especially in Europe, ultrasound is considered to play a pivotal role in the early diagnosis of developmental hip diseases [9
]. Especially in babies with risk factors associated with developmental dysplasia a careful examination is needed [11
]. General screening concepts remain controversial due to added costs [12
]. The treatment of dysplastic hips depends on the degree of subluxation. Based on the sonographic appearance the Graf classification has gained wide acceptance [14
]. While class I hips need no follow up and treatment, class II hips form a group in which the degree of abnormality and the need for treatment are less clear and remain controversial. While some authors treat class II hips showing instability [19
], others report about spontaneous recovery [20
]. For treatment purposes authors introduced abduction devices such as harnesses providing abduction and flexion [20
Graf Class II b hips are defined as hips of babies older than three month, exhibiting an alpha angle of 50–59 degrees. Radiographs show an acteabular angle of more than 30 degrees. The morphology shows a stable, but deficient bony shape of the acetabulum and femur and a broadened cartilage roof. Class IIb hips show a deficit of bony maturation and therefore need treatment options. Usually, the use of abduction devices is expanded until walking onset at approximately age 8 month. With the increased mobility of the baby, an abduction and flexion harness becomes an increasing handicap.
For treatment of Graf class IIb hips at age of walking onset an abduction splint with ball and socket joints was introduced, allowing patterns as walking and crawling under constant abduction control. However, the splint still incapacitates child movements and is generally not liked by parents and custodians. Thus, an estimated number of untreated cases can be considered leading to the research question, whether the physiologically progressing maturation of hips can be significantly improved using such abduction splints for walking children.