## 4 Discussion
The reduction in restraint by the retinacular structures during knee flexion is counteracted by the increase in joint compressive force due to the relationship of the quadriceps--pstellar tendon, resulting in almost constant restraint [62]. Overall, the results suggest that at around 25\({}^{\circ}\) of knee flexion, patella alignment is maintained by bony anatomy. A second adjustment phase is due to the elasticity of the ligaments and tendons. When quadriceps strength is at 90% with an unbalanced lateral load (90 N), the phenomenon becomes more pronounced and can occur at around 15-20\({}^{\circ}\) of knee flexion. In cases of 'high patella', the patella is unable to follow the anatomy of the bone, which can lead to dislocation [63]. The study suggests that a knee-flexion angle of 25\({}^{\circ}\) may be the most dangerous for possible patellar instability. Many studies have investigated the role of the quadriceps in patellar stabilisation and dislocation, suggesting that a balance between the forces of the individual muscle components is necessary for patellar stability. In particular, the vastus obliquus medialis fascia plays a crucial role during flexion-extension movements, assisted by the medial and lateral retinaculum [64; 65; 66]. These muscle synergies are also supported by numerous studies showing the negative effect of imbalanced forces after vastus lateralis tendon release surgery alone [67], or medial implication [68], demonstrating that a whole-joint procedure is the best solution [69; 70]. As a result, these data support both preventive and post-operative rehabilitation for patellar instability using both clinical assessment and radiological parameters [66]. Over the years, several FE models have been developed to determine bone stress shielding under pathophysiological conditions or after replacement surgery, confirming that the model appears to be an effective tool for investigating knee biomechanics [71; 72; 73]. In addition, other authors emphasise the forces due to body weight, with different effects depending on the body-mass index, which also affect both the body joint and prosthesis [74; 75]. Recently, other studies have investigated various clinical conditions using FE to study knee pathologies such as osteoarthritis, high patella, anatomical changes, and surgical reconstructions [76; 77; 78; 79]. Our results are in line with other studies, such as the cadaver study by [PERSON] et al. that showed that when a lateral displacement force (10 N) occurs, patella displacement is about 6 and 13 mm, respectively, with a normal medial patellofemoral ligament [80]. Other authors have demonstrated how lateral imbalance could reduce the force required to dislocate the patella by 10 mm at different angles, by approximately 20% [81]. The present study has several limitations. First, the FE model analysis results are highly dependent on the data input and setup of the experimental model to approximate a real joint with loads that also depend on in vivo tissue characteristics. The simulation also remains an artificial version of reality with all its limitations, including the absence of important anatomical elements in the dynamics of the joint (i.e., menisci) capable of effectively transmitting loads through the joint and absorbing shocks. In addition, as with other FE models, tissue properties were approximated and therefore the data obtained may be moderately different. The proposed finite element model was fully customised in terms of the loading conditions imposed during the simulation and was based on a single subject.