Development of the hip joint in relation to congenital dislocation.

As an introduction to the pathology and treatment of C.D.H., a simplified outline of fundamental embryologic events and growth characteristics of the hip joint (selected from past and actual bibliography) is presented. Congenital dislocation of the hip appears to be the result of various genetic, developmental, environmental and mechanical factors that affect articular structures in the perinatal period. At this time, the hip joint is anatomically and functionally more vulnerable to alterations of its normal concentric disposition. If incongruency persists, subsequent morphological changes, characteristic of dysplasia will develop. The main conclusions derived from a review of the development of the hip joint in relation to C.D.H. are: 1) The hip joint is an anatomical and functional unit derived from a common primitive blastema. 2) Primitive condensed sclerotomic mesenchyme transforms into cartilage that shapes in a genetically determined pattern to form the femur and os innominatum in continuity. 3) The joint space develops by autolytic degeneration in the 7-8 week embryo. By the 11th week, the joint cavity, evolved in the capsule lined internally by synovium, has a well differentiated labrum and ligamentum teres with the basic morphology of a developed hip joint. Only after this stage is displacement possible. 4) Depth (and stability) of the acetabulum increase with development of the glenoid labrum and cartilaginous rim (incomplete only in its inferior portion). Here a fibrous band (transverse ligament) offers less resistance to displacement, but on occasions is an anatomic barrier to concentric reduction. 5) In the early fetal period, the acetabulum is a deep set cavity, becoming shallower at the time of birth. Femoral head coverage at birth is more deficient than at any other previous or subsequent stage of development. 6) The relationship between femoral and acetabular anteversion (instability index) is more important than absolute values which are variable during intrauterine life. The degree of femoral anteversion depends on teh rotational attitude and muscular action of the extremity.(ABSTRACT TRUNCATED AT 400 WORDS)