The summation of forces on extensor mechanism should be zero according to equilibrium rules of forces before and after total knee arthroplasty based on constant extensor moment.

• 计算得到髌骨形位参数变化前后与伸膝机构相关的动力学参数，包括股四头肌力、髌韧带力及髌股关节接触压力的变化。