肥胖患者膝关节置换胫骨延长杆对胫骨应力分布影响的研究

摘要

目的 使用有限元技术来研究肥胖患者膝关节置换中胫骨侧不同长度延长杆的使用对胫骨应力分布的影响以及胫骨内翻截骨时胫骨平台所受应力变化.方法 选取1名正常健康女性志愿者,通过螺旋CT扫描,三维重建及有限元分析软件,建立三维膝关节胫骨侧模型.使用标准胫骨假体,长度60 mm,长度100 mm延长杆.建立标准平台、平台+60 mm延长杆、平台+100 mm延长杆和内翻5° 平台四组有限元模型,加载肥胖患者行走时压力,分析胫骨应力分布情况.结果 当使用60 mm及100 mm延长杆时,胫骨所承受轴向应力最高分别达到66.3 MPa和67.2 MPa,与标准平台的胫骨轴向应力(42.3 MPa)差异有统计学意义(P<0.05).当使用60 mm延长杆时,胫骨后侧平台应力为(3.12±1.20)MPa,与对照组中后侧平台应力差异有统计学意义(P<0.05);但60 mm与100 mm延长杆在后侧平台方向应力差异无统计学意义(P>0.05).在 100 mm延长杆模型中,内侧平台的应力比标准平台、60 mm延长杆组的应力明显减小(P<0.01).前侧、外侧平台的应力分布在各个模型中差异无统计学意义(P>0.05).当5° 内翻截骨时,胫骨平台内侧出现明显应力集中.结论 在数字化模型中,胫骨平台延长杆可以起到传导近端胫骨应力的作用.当胫骨平台后侧骨缺损时,建议使用60 mm延长杆分散平台应力;当胫骨平台内侧骨质条件较差时,使用100 mm延长杆才能起到分散应力的作用.%Objective Using finite element ( FE ) analysis to explore the influence of the tibial base plate with different length of stemming of total knee arthroplasty ( TKA ) in obese patients on the tibial stress distribution and variation of tibial plateau stress with varus plateau. Methods A healthy female volunteer was enrolled in the present study. First 3D FE models of the knee joint were reconstrusted on the basis of the spiral CT scans of the volunteer. Four FE models were constructed of the tibia plateau ( standard tibial base plate, tibial plate + 60 mm-long stem, tibial plate + 100 mm-long stem, standard tibial base plate with 5° varus ) to analyze the biomechanical variation in full-length tibia stress pattern. Results There were significant differences ( P < 0.05 ) in tibia stress pattern between standard tibial base plate ( 42.3 MPa ) and tibia plateau with stem of 60 mm ( 66.3 MPa ) and 100 mm ( 67.2 MPa ). Using 60 mm stem to make the posterior stress of tibia plateau much lower than other groups, but there were no significant differences between 60 mm and 100 mm. In the model of 100 mm stem, the stress of medial tibia plateau was significantly lower than the standard tibial plate and 60mm stem ( P < 0.01 ). There were no significant differences among these 3 different lengths of stems in the anterior and lateral tibia plateau. Stress of medial tibia plateau was much higher in 5°varus standard tibial base plate. Conclusions Tibia plateau vatus would increase medial stress of plateau, and using stem could transmit proximal stress to distal of tibia. The 60 mm stem is availiable for the posterior tibia bone defect, and can reduce the posterior stress. And 100 mm stem could lower the medial stress distribution of tibial plateau. Increasing the length of stem would not dismiss stress, on the contrary, long stem may cause significant stress shielding in the proximal tibia.