Acetabular Augmentation by Residual Hip Dysplasia

Residual hip dysplasia is one of the most common causes of secondary osteoarthritis of the hip joint. It is suggested that excessive hip joint contact stress due to small weight-bearing area is an important precipitating factor for the development of hip arthrosis (Hadley et al., 1990; Hipp et al., 1999; Maxian et al., 1995). Dysplasia of the hip refers to mechanical deformations and deviations in the size and shape or mutual proportions between the upper part of the femur and acetabulum (Durnin et al., 1991). The dysplastic hips are diagnosed according to anatomical changes in the hip that are visible in the radiographs (Durnin et al., 1991; Legal 1987; Pauwels, 1976). Usually, the center-edge angle of Wiberg (θCE) is used as the main radiographic parameter for the assessment of the hip dysplasia (Legal 1987; Pauwels, 1976 ). The range of θCE from 20–25° is considered as the lower limit for normal hips, while the value of θCE below 20° is pathognomonic for the hip dysplasia (Legal 1987). The size of the angle θCE correlates with the size of the weight bearing area and may therefore serve as an indirect measure of the hip joint contact stress (Brinckmann et al., 1981; Hipp, 1999; Iglic et al., 1993; Kummer 1988; Malvitz & Weinstein, 1994). However, it was suggested that besides θCE other geometrical parameters such as the radius of the femoral head (Brinckmann et al., 1981; Legal 1987) or the pelvic shape (Iglic et al., 1993, 2001; Kersnic et al., 1997) should be taken into account in assessment of the contact stress distribution. Therefore, the direct calculation of the contact stress in the hip joint has been introduced in the assessment of the biomechanical status of the hip (Brinckmann et al., 1981; Kummer, 1991;Legal 1987; Vengust, 2001) (Fig.1).