Do Kinematics or Muscle Function During Sit-to-Stand Change Following a Primary Total Knee Arthroplasty?

Sit-to-stand (STS) transfer is essential for independent living and mobility in daily life but challenging for individuals before and after total knee arthroplasty (TKA). It remains unclear whether deficits in individual muscle function contribute to the lack of improvement in STS performance following TKA. The objective of this study was to determine whether lower extremity kinematics, muscle function during STS (quantified by muscle forces and muscle contributions to acceleration), and knee extension strength change following TKA. Dynamic musculoskeletal simulations of STS were performed for seven individuals before and six months after surgery. Computed muscle control and induced acceleration analysis were used to determine individual muscle forces and contributions to center of mass acceleration, respectively. Overall kinematic strategy did not largely change following TKA, and we found no change in muscle forces, muscle contributions, or knee extension strength following TKA, suggesting a consistent movement strategy to compensate for persistent quadriceps weakness. Both before and after TKA, the psoas, gluteus medius, vastus medialis and lateralis, and soleus produced the largest forces, while the gluteus maximus and biceps femoris produced smaller forces. Large braking contributions to acceleration from several muscles and small gluteus maximus contributions to forward and upward acceleration observed at both time points may contribute to the persistent functional performance deficits often observed in patients with a TKA. These findings demonstrate that overall movement strategy during STS (quantified by kinematics and muscle function) and knee extension strength did not change within six months following TKA, which may inform post-operative rehabilitation programs.