# Finite Element Analysis of a Novel Approach for Knee and Ankle Protection during Landing
## 4 Discussion
Thus, the average horizontal force on the talus was calculated, and the results showed that, although the average horizontal force increased substantially as the jump height increased, wearing the brace could still evidently reduce the horizontal force at all three heights compared to not wearing the brace. We inferred the main reason as being also that the semi-rigid brace at the ankle joint transferred the GRF, resulting in a reduction in the force acting on the foot. With respect to ankle protection, our brace is in sharp contrast to prophylactic braces in previous studies [38; 39; 40]; that is, our brace reduces the risk of ankle injury by sharing and transferring the GRF with little effect on the joint ROM, which is attributed to the minor restriction exerted by the brace on the joint. It is known that the knee is the second most frequent injury site during drop landing [6; 41]. Landing injuries of knee include knee dislocation, cartilage fracture, ligament sprain, and meniscus damage, among which cartilage fracture and meniscus damage are considered to be serious injuries [42]. Therefore, in this study, we investigated the biomechanical responses of the articular cartilages and menisci, finding a rapid increase in stress peak with increasing jump height whether or not the brace was worn. However, the brace could reduce the risk of knee injury by reducing the peak von Mises stress of the menisci and articular cartilages at 0.4 m, 0.8 m, and 1.2 m. The reduction in knee internal stress was expected, because the presence of the ankle semi-rigid brace absorbed some of the GRF, thereby reducing the GRF acting on the lower limbs. A similar protective effect can be achieved with a functional knee brace, as found in [43], where the peak vGRFs were significantly reduced during drop jump landing. In contrast, our designed brace does not limit the ROM as much as a functional knee brace, which is more in line with the participant's desired motion. Furthermore, in the absence of our brace, the stress on the medial meniscus was apparently higher than that of the lateral meniscus, thus, rendering the medial meniscus more vulnerable to damage. This is in agreement with the opinion of [44] on human knee osteoarthritis, where the authors mentioned that 60% of load goes through the medial side of the knee during walking, and disease most often presents in the medial compartment of the joint. On the other hand, with the brace, the contact areas between the medial articular cartilage and meniscus decreased, while the lateral contact area increased, resulting in a more balanced load bearing of the medial and lateral meniscus. It is logical to argue that the retractive force attributed to an elongated spring component at the knee bending balanced the high impact experienced by the knee joint, converting some kinetic energy into elastic potential energy of the spring, thereby achieving a protective effect. This seems to be comparable to a previous study [45] on medial knee osteoarthritis rehabilitation, where the authors found that, with a laterally wedged insole (LWI), the von Mises stress at the medial femur cartilage region and the medial meniscus significantly decreased. Similarly, both an LWI and our brace can redistribute the knee internal loading and relieve the stress at the medial compartment of the knee. In summary, this brace can be used as a parallel structure in the lower extremities with little constraint on the joint ROM, helping dissipate the GRF and reduce the force acting on the human body, in a similar way to cats having more limbs to cushion the impact [46]. There were some limitations in the context of model simplifications and settings. All bony tissues were assumed to be homogeneous, isotropic, and linear-elastic materials. Moreover, the ligaments were defined with tension-only truss elements, which may have resulted in stress concentration at the insertions.