CELLULAR & MOLECULAR BIOLOGY LETTERS * Corresponding author 311 HIP BIOMECHANICS IN ORTHOPAEDIC CLINICAL PRACTICE VANE ANTOLIC 1 *, VERONIKA KRALJ-IGLIC 1, 2 , ALES IGLIC 3 and BORUT POMPE 1 1 Department of Orthopaedic Surgery, University Medical Centre Ljubljana, Zaloska 9, SI-1000 Ljubljana, Slovenia, 2 Institute of Biophysics, Faculty of Medicine, University of Ljubljana, SI-1000 Ljubljana, Slovenia, 3 Laboratory of Applied Physics, Faculty of Electrical Engineering, University of Ljubljana, SI- 1000 Ljubljana, Slovenia Abstract: Radiographic and clinical studies, coupled with biomechanical assessment of the hip, are important tools for predicting the development of osteoarthitis of the hip. In order to better understand the treatment of hip dysplasia, it is necessary to determine the contact stress in the hip joint. In this study, a three-dimensional mathematical model was used to determine hip joint contact stress. Because of the discrepancy in the results of analyses of different radiographic indicators of hip dysplasia, the calculation of hip joint contact stress is proposed for a more accurate assessment of the severity of hip dysplasia. Key Words: Hip, Biomechanics, Dysplasia, X-ray Parameters INTRODUCTION High contact stress in the articular surface leads to the degeneration of the articular cartilage, resulting in osteoarthitis [1]. The hallmarks of hip osteoarthritis include pain and reduced range of motion. The disease accounts for more dependency in walking, stair climbing, and other lower extremity tasks than any other disease, particularly in the elderly. The i ncidence rate of hip arthrosis is 400 to 600 per 100,000 person-years. In over 55-year-olds, the prevalence of mild and severe osteoarthrosis is 5-11% and 1-3.5%, respectively, for men and 2-26% and 0.5-10% for women. Increased hip joint contact stress is associated with an increased magnitude of articular resultant force and/or a small weight-bearing area of the hip joint. Preventive orthopaedic surgery aimed at changing the geometry of the hip joint can reduce hip joint contact stress and postpone, or even prevent the development of hip osteoarthitis. For proper planning of surgery, it is imperative to determine the preoperative hip contact stress and evaluate changes in hip geometry induced by surgery. In everyday clinical practice, hip forces and stresses can only be assessed by mathematical modelling [1, 2]. Our group has developed a clinically applicable mathematical model of hip forces, which takes into account the three-