Biomechanical analysis of triple pelvic osteotomy

Introduction. Hip joint incongruence is found in a number of hip joint disorders in childhood and adolescence. Altered hip joint compression force overcomes the adaptive capacity of joint cartilage, inevitably leading to degenerative joint changes and early invalidity. Most utilized method for operative treatment of this impairment that we use in adolescent age is Tennis triple pelvic osteotomy. The effects of operative treatment can be objectively analyzed by numeric and analytic hip joint mathematical models. The mathematical model most used in hip joint biomechanical functional analysis is three-dimensional radiography-based model. It has been widely applied to normal hips and hips operated by various methods. However, it has not been applied to Tennis triple pelvic osteotomy. Goals. To apply three-dimensional radiography-based mathematical model of the hip joint to standard anterioposterior pelvis and hip radiography, before and after triple pelvic osteotomy, to calculate parameters of contact hip stress distribution (direction, angle and intensity of resultant hip force, angle and magnitude of peak contact hip stress, the index of the hip stress gradient), and to analyze the relationship of biomechanical parameters to patients’ standard clinical and radiographic data. Material and method. Out of 92 patients with hip joint incongruence in adolescent age (due to developmental disease of the hip, postreductional avascular necrosis of femoral head or Leg-Calvé-Perthes disease), operated by Tönnis triple pelvic osteotomy at the Institute for Orthopaedic Surgery “Banjica” in Belgrade in the period from 1996. to 2011, 75 hips (60 patients) were included in the test group, with average Wiberg CE angle of 15,18+/-9,31°. All contralateral hips were also analyzed, and then divided in negative control group (healthy hips, 19 cases) and positive control group (deformed hips, 56 cases). The three-dimensional radiography-based mathematical model of the hip joint described by Iglič et al. (1990) was applied to all the hips, at preoperative, postoperative and final examination. All collected data were described by standard descriptive statistical tools, and analyzed by appropriate statistical tests. Results and discussion. At postoperative measurements we found that CE angle increased reaching normal values (median 33.45%), angle of peak hip pressure pole (Θ-pol) was lower for 63.5% (from 43.440 to 15.850, p