Simulation of Quadriceps Strengthening Exercise Following Total Knee Replacement- Effects on Patellofemoral Contact Mechanics

Total knee replacement (TKR) surgery is a common treatment for severe osteoarthritis patients. After surgery, quadriceps strengthening exercise is often recommended in order to rebuild the muscle function and speed up the recovery. There are, however, concerns over the deteriorating side effects that this exercise might cause in the patellafemoral joint (PFJ). The purpose of this research was to study the effects of quadriceps strengthening exercise on the contact mechanics of the PFJ of TKR patients. An open-source musculoskeletal -multi body dynamics model was employed to obtain the muscle, ligament and contact forces of a total knee replaced joint. The results were then utilized as the inputs of a detailed finite element model of the knee including the TKR components, tendons and ligaments. The quadriceps strengthening exercise was simulated by extending the knee from 90 degrees flexion with a zero to 4 Kg extra weight applied on the ankle. Results indicated a $\mathbf{7 . 2 \%}$ increase in the maximum contact pressure of the patellar component per kilogram extra weight. The increase of the patellar contact pressure was associated with the increasing contact force and contact area with added extra weight. However, the slight increase of the contact area could not compensate the large increase of the contact force (at a rate of $3.8 \%$ per kilogram extra weight). It was concluded that care should be taken in recommending the quadriceps strengthening exercise to the TKR patients to avoid the risk of patellar component failure which might lead to a revision surgery.