定制型膝关节假体修复股骨远端骨缺损假体柄长的有限元分析

以男性健康自愿者右股骨的CT图像为原始数据，分别建立柄长150，160，170，180，190 mm的定制型膝关节假体修复重建股骨远端40%骨缺损的三维有限元模型，对应的股骨干截骨长度分别为160，170，180，190，200 mm，加载平地慢速(3 km/h)行走步态周期中下肢4倍体质量负荷。皮质骨最大应力出现在股骨近端内侧，随假体柄长由150 mm增加至190 mm，应力最大值由106.8 MPa减少至91.78 MPa。骨水泥最大应力出现在骨水泥上1/4段内侧，应力最大值由 27.2 MPa减少至19.06 MPa。假体柄承载最大负荷，应力值变化不明显。5个模型出现骨折、骨水泥碎裂及假体柄断裂概率均较小。提示定制型膝关节假体重建保肢符合人体生物力学规律；短柄假体可引起骨、骨水泥应力集中，重建后发生骨折、骨水泥碎裂风险较高，而增加柄长对骨的应力遮挡水平也相应增大。

Finite element analysis of custom endoprosthesis stem length in distal femur reconstruction

Based on CT images of the right femur of male healthy volunteer, five three-dimensional finite element models A, B, C, D, E were developed using different stem-length (150 mm, 160 mm, 170 mm, 180 mm, 190 mm) custom endoprostheses to reconstruct 40% defect of the distal femur. The corresponding osteotomy length of the femoral shaft was 160, 170, 180, 190 and 200 mm. Four times of body mass load corresponding to the normal walking gait cycle (3 km/h) was applied. The maximum stress on the bone recorded in the medial proximal femur dropped from 106.8 Mpa to 91.78 Mpa when the stem-length increased from 150 mm to 190 mm. While the maximum stress on the cement recorded in the top one fourth medial dropped from 27.2 Mpa to 19.06 Mpa. Compared to the bone and cement the stress on the stem was greater but had few changes. No bone fracture, cement damage or stem failure occurred in all models. Using custom endoprostheses to reconstruct defect of the distal femur has good biomechanical foundation. Short stems could induce concentrated stress in the bone and cement, easily leading to bone fracture and cement damage. Increasing the length of the intramedullary stem often increases the level of the stress-shielding on the bone.