Computer Determination of Contact Stress Distribution and Size of Weight Bearing Area in the Human Hip Joint

Abstract

The mathematical models and the corresponding computer program for determination of the hip joint contact force, the contact stress distribution, and the size of the weight bearing area from a standard anteroposterior radiograph are described. The described method can be applied in clinical practice to predict an optimal stress distribution after different operative interventions in the hip joint and to analyze the short and long term outcome of the treatment of various pathological conditions in the hip. A group of dysplastic hips and a group of normal hips were examined, with respect to the peak contact stress normalized by the body weight, and with respect to the functional angle of the weight bearing area. It is shown that both these parameters can be used in the assessment of hip dysplasia.

Dynamic femoral head translations in dysplastic hips

“…Several radiographic indices are used to evaluate DDH and to quantify acetabular coverage after osteotomy. The CE angle is an objective measure used to diagnose DDH (Iglic et al, 2002;Mavcic and Pompe, 2002;Mavcic et al, 2000). AHI quantifies relative acetabular support, and ARO and Sharp angles express acetabular inclination.…”

Acetabular Augmentation by Residual Hip Dysplasia

“…the original acetabular roof, were noted in our study, which suggests that no significant joint cartilage degeneration occurred during the follow-up period. Reduction in the median peak stress on the hip weight-bearing area was obtained in SAA and Bernese osteotomy with the use of the above described mathematical model Iglič et al,2002). The greatest influence on the peak stress is exerted by the radius of the femoral head, followed by the interhip distance, the position of the attachment point of the muscles on the greater trochanter and the pelvic height and width.…”

“…The angle ϑR is taken to be positive in the medial direction from the vertical axis and negativ in the lateral direction from the vertical axis Iglič et al, 1993a). In the second step the mathematical model for calculation of the stress distribution in the hip joint Iglič et al, 2002;Ipavec et al, 1999) is used. The model assumes the non-uniform distribution of the contact stress (Ipavec et al, 1999).…”

“…Therefore in the second mathematical model for determination of the contact stress distribution Iglič et al, 2002) the force R is assumed to lie in the frontal plane. The hip joint reaction force in the frontal plane can be expressed by its magnitude (R) and by its inclination in the frontal plane with respect to the vertical plane ϑR (Fig.…”

“…Peak contact stress in the weight bearing area of the hip (p max ) was calculated using a computer program, HIPSTRESS Iglič et al, 2002). The program consists of two procedures.…”