Biomechanical analysis and clinical efficacy of eccentric rotational acetabular osteotomy

Abstract

Objective To investigate the biomechanical mechanism and report preliminary clinical efficacy of eccentric rotational acetabular osteotomy (ERAO) when conduct treatment for developmental dysplasia of the hip (DDH). Methods Biome-chanical model of the hip joint was established on six female cadaveric hips embalmed by formalin and stimulate ERAO was then performed on the model. Vertical force was loaded on the cadaveric spine from 0 N to 500 N and strain value on femoral head was measured preoperatively and postoperatively when loading force on spine reached the point of 100, 200, 300, 400 and 500 N. Stress value were then calculated base on the measurements. Besides, we reported postoperative follow-up cases which were underwent ERAO to treat DDH in our hospital from July 2007 to October 2014. A total of 25 patients (26 hips) were reported, including 6 males and 19 females. Age varies from 11 to 57 years old, and the average age was 31 years old. Postoperative hip function was evaluated by Harris hip score and anteroposterior X-ray of pelvic was taken preoperatively and postoperatively to measure the acetabular-head index (AHI), CE angle and sharp angle. Results Preoperative stress increased when loaded on spine became larger, but postoperative stress changed its increasing trend into decreasing when the load was greater than 300 N (turning point), which showed a parabolic trend. Compared with the preoperative stress under different load varying from 100 N to 500 N, postoperative stress was not statistically significant. Meanwhile, by the end of follow-up period, 18 patients (19 hips) were followed form 7 to 85 months. The average follow-up time was 40 months and the follow-up rate was 72%. Harris hip score improved from preoperative 64.3±7.2 points to 85.6±5.3 points; postoperative AHI increased an average of 36.5%, CE angle increased an average of 33.1° and sharp angle reduced an average of 12.3°. All differences between preand post-operative indexes were statistically significant. Conclusion ERAO has the ability to correct the deformity of acetabulum. It enlarges the acetabular coverage of the femoral head and thus reduces the pressure of weight-bearing area. Key words: Hip dislocation, congenital; Osteotomy; Acetabulum; Biomechanics