The role of cannulated compression screws in the treatment of nontraumatic necrosis of the femoral head with allogeneic fibular graft: a biomechanical analysis

Abstract

Purpose To explore the biomechanical effect and mechanism of cannulated compression screw in the treatment of non traumatic necrosis of femoral head with allogeneic fibula graft. Methods Based on the CT data of healthy adults, four groups of models were established by using finite element software: the normal group, the femoral head necrosis group, the hip preservation operation group with allogeneic fibula graft (later referred to as group A), and the hollow compression screw combined with allogeneic fibula graft (later referred to as group B). Apply 1440N, 2400N and 4200N loads to the four groups of models respectively, observe the changes of stress distribution on the surface and deep of the femoral head, internal mechanical transmission pathway in different groups under different loads, as well as the displacement of implants in the two groups of surgical models, and explore the biomechanical role and mechanism of hollow compression screws in the same kind of allogeneic fibula graft. Results (1) Under normal circumstances, the pressure of the femoral head surface and internal cancellous bone is mainly concentrated in the anterolateral weight-bearing area of the femoral head, and the internal stress can be well transmitted to the lower limbs through the femoral calcar, femoral neck and other parts, without obvious stress conduction barrier.(2) The closer the necrotic location is to the anterolateral column of the weight-bearing area, the stress peaks of the cartilage, cortical bone and cancellous bone on the surface of the femoral head increase significantly compared with the normal model. With the increase of load, the stress peaks of the above bones increase significantly. In type C1 and C2 necrosis, the stress transmission of femoral head and neck was abnormal, and the stress concentration occurred in the normal bone around the necrotic area.(3) Under different loads, the peak value of von Mises stress in type C1 necrotic area in group B decreased by 1.67mpa (-18.45%), 2.77mpa (-18.37%), 4.84mpa (-18.35%) respectively compared with group A. the peak value of von Mises stress in type C2 necrotic area in group B decreased by 0.05Mpa (-0.58%), 0.08mpa (-0.56%), 0.15Mpa (-0.6%) respectively compared with group A; At the same time, under different loads, the displacement distance of type C1 allogeneic fibula strips in group B decreased by 0.06mm (-8.7%), 0.1mm (-8.7%) and 0.17mm (-8.42%) respectively compared with group A. the displacement distance of type C2 allogeneic fibula strips in group B decreased by 0.01mm (-1.72%), 0.01mm (-1.03%) and 0.02mm (-1.19%) respectively compared with group A. Conclusion In the allogeneic fibula graft surgery, the addition of cannulated screws may have a better mechanical effect of dispersing the stress in the necrotic area and stabilizing the fibula strip, which is most significant in type C1 necrosis.