## 4 Discussion
If the different level of the total resulting forces is considered, the curves of medial and lateral tibial contact forces are similar for the present study compared to [PERSON] et al. [47]. The medial force ratio in the tibia was 40% at the instant of maximum total contact forces, which fits well to the 42% \(\pm\) 8% which were given by [PERSON] et al. [47]. The varus-valgus moment is changing its sign from negative to positive at 75\({}^{\circ}\) of flexion during knee bend. This results in a switch of the dominant tibiofemoral contact force from the medial to the lateral conodyle, as shown in Figure 6. Therefore, the most loaded conodyle in a deep knee bend cycle is the lateral one. At first glance, this might be inconsistent with the fact that in most patients, the medial conodyle is more affected by osteoarthritis than the lateral one [48] and 90-95% of unicompartmental knee arthroplasties are placed on the medial side [49]. A deeper look into data from instrumented knee implants [31] shows positive varus-valgus moments mainly for deep flexion angles in symmetric two-legged load cycles, such as knee bend, sit down, and stand up from a chair. The lower relative prevalence of these cycles, compared to level walking, stairs up, and stairs down cycles, with high negative varus-valgus moments explain the higher risk of osteoarthritis on the medial conodyle. For the sit down and stand up cycles, the results are also in good agreement with the given data from [PERSON] et al. [47]. For two of the eight patients that were included into the standardized loads from [PERSON] et al. [31], a subject-specific calculation was made by [PERSON] et al. [50]. They calculated 3.2 BW as averaged peak patellofemoral contact force during a squat at a flexion angle of 94\({}^{\circ}\). Their results for the two patients were 2.6 BW and 3.7 BW. The maximum of 2.6 BW for the patella contact force at 91.4\({}^{\circ}\) of flexion that was detected in the present study is equal to the lower bound of the study stated above. Research from other groups, with different patient cohorts, showed patellofemoral forces for a squat at 100\({}^{\circ}\) of flexion in a range of 2.7 BW to 3.5 BW [51; 52]. Compared to the given literature values, the results of the herein described simulation approach show good agreement, especially for high flexion angles, where the most critical loads are reached. Therefore, the model demonstrates potential to be a useful tool to evaluate implant designs in a platform development approach of new knee systems. It is possible to fully automate the simulation process, which makes it possible to test a great number of geometries in an efficient way. To improve the model, additional validation steps can be performed in future with the CAMS-Knee dataset. This dataset contains tibial loads and kinematics data measured by video fluoroscopy [53]. Further development of this methodology can enable implant manufacturers to achieve more realistic kinematic behavior on a systematic scale by considering dynamic loading and tibo- and patellofemoral kinematics, as well as contact mechanics in a standardized workflow. Especially in combination with a second model, which will be able to handle load cycles with dynamic ground reaction forces but dispenses with considering the patella, this method opens a wide field of subjects to investigate in an efficient way--from effects of design changes in patellar and trochlear geometries to the impact of different alignment methods. The analysis of patellar kinematics shows the effects of proximo-distal patellar position and patellar tendon stiffness. According to patellar flexion, both patella baja and high patellar tendon stiffness lead to an increase in relative patellar flexion angles. Therefore, problems occurring in knees with patella baja for high flexion angles could also occur in knees with a central patellar position and a very strong patellar tendon. A weak patellar tendon also increases patellar spin and has minor effects on patellar tilt and shift.