Hip joint contact stress as an additional parameter for determining hip dysplasia in adults: comparison with Severin's classification.

BACKGROUND The hip's biomechanical state affects its future development. Therefore, a relevant biomechanical evaluation would be of use in assessing hip dysplasia. Recently, a noninvasive method was developed to determine stress on the weight-bearing area of the hip. The biomechanical assessment was compared with Severin's radiographic classification. MATERIAL/METHODS Standard anteroposterior radiographs, taken prior to surgery, of 35 adult patients who were treated for hip dysplasia were analyzed. The AP radiographs of 59 hips were classified into groups 1-3 according to Severin's classification. The geometrical and biomechanical parameters of the hips within each of Severin's groups were compared. RESULTS The differences between the mean peak stress on the weight-bearing area of the hip and the peak stress normalized to body weight of both the first and second groups compared with the third group were highly statistically significant. All three of Severin's groups had stress readings ranging from 2 to 4 MPa. CONCLUSIONS This study shows that, in general, the biomechanical results corresponded to the results obtained by Severin's evaluation; however, when assessing an individual hip, important differences may be present. Since all of Severin's groups had a stress reading ranging from 2 to 4 MPa, it would be useful to determine the hip's stress distribution when determining treatment.