Objective: To investigate the validity of improving the femur's mechanical characteristics by implanting calcium phosphate ceramic screws after removing dynamic hip screw (DHS).
Methods: The three dimensional finite element model of the femur was built based on the CT scanning of a normal male volunteer. Then the models of the femur with and without DHS were established. According to calcium phosphate ceramic screws with porosity and apparent elastic modulus, 80% and 0.1 GPa were set as group A, 50% and 1.0 GPa as group B, and 30% and 1.5 GPa as group C. Von Mises stress distribution and maximum stress were recorded when the joint was maximally loaded in a gait cycle.
Results: The Von Mises in normal femoral shaft was uniform; no phenomena of stress concentration was observed and the maximum stress located at the joint load-bearing site of the proximal femur. The stress concentration was observed in the femur without DHS, and the maximum stress located at the distal femur around the screw hole. By comparing several different calcium phosphate ceramic screws, the stress distribution of group B was similar to normal femur model, and the maximum stress located at the joint load-bearing site. The other screws of groups A and C showed varying degrees of stress concentration.
Conclusion: Implanting calcium phosphate ceramic screw can improve the mechanical characteristics of the femur after removing dynamic hip screw, and the calcium phosphate ceramic screw with 50% porosity and 1.0 GPa apparent elastic modulus is suitable for implanting.
目的: 探讨动力髋螺钉取出后，在股骨残留钉道内植入多孔羟基磷灰石（hydroxyapatite，HA）陶瓷钉棒对于改善股骨力学性质的有效性研究。.
方法: 选取 1 名健康成年男性志愿者并行股骨 CT 扫描，利用 CT 数据建立正常股骨三维有限元模型，并在此基础上分别建立未填充钉棒股骨模型、填充多孔 HA 陶瓷钉棒股骨模型。根据填充多孔 HA 陶瓷的表观弹性模量和孔隙率的不同，将填充孔隙率为 80%、表观弹性模量为 0.1 GPa 的多孔 HA 陶瓷设为 A 组；填充孔隙率为 50%、表观弹性模量为 1.0 GPa 的多孔HA陶瓷设为 B 组；填充孔隙率为30%、表观弹性模量为 1.5 GPa 的多孔 HA 陶瓷设为 C 组。将成人步态周期中关节承载处于峰值时刻作为边界条件，记录 Von Mises 应力分布及应力峰值。.
结果: 正常股骨模型最大应力出现在股骨近端关节承重处，股骨干应力分布均匀，未出现应力集中现象。未填充钉棒股骨模型最大应力出现在远端钉道周围的骨皮质处，出现了明显的应力集中现象。B 组多孔 HA 陶瓷植入的股骨模型其应力分布与正常股骨模型应力分布最为接近，最大应力出现在关节承重处；A、C 组多孔HA陶瓷模型中均出现了不同程度的应力集中现象。.
结论: 在取出动力髋螺钉的股骨缺损处填充多孔 HA 陶瓷钉棒能明显改善股骨力学性质，其中孔隙率 50%、表观弹性模量 1.0 GPa 的多孔HA陶瓷钉棒最适合作为股骨的填充钉。.
Keywords: Femoral intertrochanteric fracture; calcium phosphate ceramics; dynamic hip screw; three dimensional finite element analysis method.