Design And Related Study Of Dynamic Hip External Fixator

Objective: On basis of anatomic character and movement of hip in Chinese people, dynamic hip external fixators (DHEF) were designed to decrease the pressure of femoral head by hip distraction and the hip functional exercise. The related three-dimensional finite element analysis, biomechanical experiment and clinical application were carried out.Methods: DHEF suitable for hip of Chinese people was designed and manufactured, and related study in three-dimension finite element analysis, biomechanics and clinical application was performed. The study was divided into four parts. Part one-The design of DHEF: On basis of related literature and measurement of hip, data on the anatomic character for hip was summarized and measured. DHEF suitable for hip of Chinese people was designed. The function and characters of DHEF were described. Part two-The three-dimensional finite element analysis: Normal hip models and hip models with type A DHEF with single-axis, type B DHEF with double-axis were established to observe and analyze pressure on femoral head in double-leg stance, single-leg stance (neutral, extension 5, flexion 10, flexion 30° ). The results were statisticly analyzed. Part three-The biomechanical study of DHEF: The pressure sensitive film layers were cut into rosette patterns based on the femoral head diameter and easily fixed around femoral head. Firstly, we used pressure sensitive film to measure contact pressures in 8 hip joints from 4 cadavers under normal loading (including double-leg stance, single-leg stance) through L5. Secondly, 8 hip joints were randomly divided into group A and group B (each group has 4 joints) . Group A was fixed with type A DHEF, while group B was done with type B DHEF. Under the distraction for 5mm, pressures had been measured in the two conditionsmentioned above. The results were statisticly analyzed. Part four-Clinical application: 4 cases with osteonecrosis of femoral head in young patients were treated with vascular iliac bone graft assisted by DHEF. The dead bone was erased in femoral head, and empty was filled with vascular iliac bone graft. The space of hip joint was distracted with type A DHEF. The follow-up and imageologic study after operation had been carried out.Results: DHEF is suitable for anatomic character and movement of hip in Chinese people. The three-dimension finite element analysis and biomechanical study showed that DHEF ( both type A and type B) can decrease hip joint force under normal loading (P<0.05, comparing with the normal loading condition without external fixators.), especially in double-leg stance. Type B DHEF can decrease the pressure of femoral head more greatly than Type A. In addition, the clinical study showed no collapse occurred in patients during postoperative 12-24 months, and hip function was restored to normal through early functional exercise. DHEF can assist on treating osteonecrosis of femoral head. Conclusion: DHEF is suitable for anatomic character and movement of hip in Chinese people. It is effective biomechanical stability for hip. DHEF can decrease the pressure of femoral head under normal loading, which can assist on treating hip disease. It not only decrease the collapsing rate of femoral head, but also permit hip to do functional exercise.