膝关节单髁置换界面应力失效分析

目的 分析骨水泥型胫骨假体平台界面应力，确定界面应力损伤区域，为临床单髁置换胫骨平台的应力失效问题提供参考。方法 通过人体动力学软件模拟完整周期的步态，获得膝关节的承力条件；利用医学影像及三维重建软件建立完整的膝关节模型并进行单髁置换；通过有限元法分析单髁置换后胫骨假体平台界面应力的分布规律。结果 步态下膝关节的力和角度随时间呈周期性变化，1.3 s为1个周期，膝关节合力峰值为760 N；界面最大剪切应力为11.82 MPa、最大拉应力6.849 MPa，均发生在假体-骨水泥界面的内侧前端拐角处；对于界面的最大应力，钛合金假体低于不锈钢假体。结论 假体的弹性模量减小可以降低界面最大主应力，从界面应力考虑，钛合金假体优于不锈钢假体；胫骨假体平台界面损伤区域主要在内侧前、后端拐角和外侧中端处，故提高该区域假体-骨水泥结合能力能防止单髁膝关节胫骨假体平台松动。研究结果对临床中单髁术后胫骨假体平台松动预防具有实际意义。

Failure Analysis on Interface Stress in Unicompartmental Knee Arthroplasty

Objective To analyze interface stress of cemented tibial prosthesis platform and determine the interface stress damage area, so as to provide references for stress failure of tibial platform in clinical single condylar replacement. Methods The full cycle gait was simulated by human dynamics software to obtain the load-bearing condition of knee joint. A complete model of the knee joint was established by medical imaging and three-dimensional (3D) reconstruction software, and unicompartmental replacement was performed. The distribution of interfacial stress of tibial prosthesis platform after single condylar replacement was analyzed by finite element method. ResultsIn gait, force and angle of the knee joint changed periodically with time, a cycle lasted 1.3 s, and the peak of knee joint resultant force was 760 N. The maximum shear stress of the interface was 11.82 MPa and the maximum tensile stress was 6.849 MPa, both occurred at inner front end of the corner of prosthesis cement interface. The maximum interface stress of titanium alloy prosthesis was lower than that of stainless steel prosthesis. Conclusions The decrease in elastic modulus of prosthesis can reduce the maximum principal stress at the interface. Considering the interface stress, titanium alloy prosthesis is better than stainless steel prosthesis. The area of tibial prosthetic platform interface damage is mainly at the medial anterior and posterior corners and lateral middle ends,so improving the ability of prosthesis cement bonding in this area can prevent the loosening of tibial prosthesis of unicompartmental knee joint.The findings have practical implications for the prevention of tibial prosthetic platform loosening after unicompartmental knee arthroplasty in clinic.