Development of bony acetabulum in newborns with developmental hip dysplasia.

Trend in the development of bony acetabulum in newborns with developmental hip dysplasia was examined during the first year of life. The study comprised 120 newborns with developmental hip dysplasia. The degree of dysplasia was determined by measuring the acetabular angle (AC) on X-rays of the hips in the anteroposterior projection. The experimental trend curve was most adequate for both the whole group and each subject. The coefficient of trend was assessed by specially designed iterative method. The exhibited trend form allows the extrapolation and prognosis of treatment outcome already after 3-5 measurements of the AC angle. The applied iterative method for the determination of the coefficient of exponential trend iterated rather quickly. The chosen form of the trend curve proved to be adequate for manifestations in which a constant value is expected after a longer period of time. The exponential curve represents a mathematical model of the acetabular development dynamics, with allometric exponents and coefficients of the equation being numerical parameters that define developmental changes. As the AC angle reaches the constant value with the closure of triradiate cartilage, this parameter is an objective measure of the development of bony acetabulum. When assessing the acetabular growth in developmental dysplasia it is necessary to bear in mind that duration, specific position and quantity of newly formed and remodelled bone are determined genetically, and that external factors have a significant influence on the definitive formation.