Biomechanical indicators for accelerating and decelerating running for differentiating between fast and slow running

BACKGROUND For hip dysplastic arthroplasty, it is more widely agreed that the cup should be put into the primary rotational center of the acetabulum. Based on this we have developed the Roof Step Cut technique which the acetabulum roof defect is fixed with an L-shaped autologous graft. Since the similar graft was also reported by Radojević before, aim of this study is to compare the biomechanical characteristics of these two techniques. METHODS The study is divided into three parts: (1) Cadaver test. 10 models according to both techniques were prepared in the biomechanical laboratory of our university. Cranial force was applied on the grafts and the force required to drive 1.0 mm displacement was recorded by Instron 8874 system. (2) Stress distribution study. Vertical load (0-200N) was applied to the top border of each plexiglass model, through polarized light the fringe patterns which represented the stress distribution was observed by naked eye. (3) Finite element analysis. Subject-specific dysplastic hip was generated based on CT scan and finite element models were developed based on the two techniques. The total deformation and equivalent stress of the screws were compared under the same load. RESULTS To produce 1.0 mm displacement of the graft, the mean compression force of the Radojević’s technique was 529.2±234.6 N, and for Roof Step Cut technique it was 419.0±69.13 N (P=0.347). The plexiglass models showed in Radojević’s technique much more dense fringe patterns were observed at all contact areas, indicating more stress distribution. Finite element analysis showed that during the loading process, even though the RSC model generated more deformation, the stress level was much lower. The Radojević’s model behaved very rigidly, the stress increase characteristic and its location on the screw showed potential problem for future stability. CONCLUSIONS The Roof Step Cut technique showed more biomechanical advantages than Radojević’s technique. With less stress between the graft and host bone, as well as on the screw, it may favor the general stability in the long run.