# Simulation Analysis of Knee Ligaments in the Landing Phase of Freestyle Skiing Aerial
## 5 Conclusions  
Although neutral landing had the greatest peak stress on the medial meniscus, stress on the ACL, PCL, MCL, and LCL were at their least of the three scenarios due to the slight relative displacement of the tibia, so neutral landing should be considered the safest and most successful technique of all three forms of landing.  
During forward landing, a part of the femoral cartilage contacted with the front end of the meniscus, causing inward horizontal displacement of the meniscus. This allowed a greater likelihood that the medial meniscus would crush the MCL. The position of stress concentration in the medial meniscus was close to the anterior horn and middle edge, causing a high risk of meniscal damage. As the knee undergoes flexion, the tibia adjusted to a neutral position under action of the posterior thigh muscle. Therefore, athletes that have weakness in their posterior thigh muscle should avoid forward landing in order to reduce the possibility of PCL or MCL injury.  
In backward landing, elastic deformation at the back of the skis created a cushion effect with deformation forces causing the tibia to move forward slightly. The tibia can be adjusted to a neutral  
\begin{table}
\begin{tabular}{c c c c} \hline
**Type** & **Neutral Landing** & **Forward Landing** & **Backward Landing** \\ \hline ACL & 3.16 & 4.01 & 4.52 \\ PCL & 6.61 & 6.81 & 6.99 \\ MCL & 2.49 & 1.96 & 3.46 \\ LCL & 1.67 & 1.60 & 1.39 \\ \hline \end{tabular}
\end{table}
Table 1: The stresses of the ligaments in three cases. (MPa).  
position only using the power of an athlete's anterior thigh muscles. Therefore, those aerialists that have weak anterior thigh muscles should avoid backward landings to reduce the risk of ACL injury.  
No matter which landing condition is adopted, due to the forward velocity and rotational inertia of the lower limbs, under the combined action of the reaction force of the landing slope and friction between the skis and surface of the snow, shear force is evident on the tibial plateau with a trend of forward and backward displacement. In this study, internal and external rotations of the tibia were not considered. If tibial rotation occurs on landing, risk of cruciate ligament injury is greatly increased [26].  
Peak stress on the tibial plateau and meniscus is extremely large. The medial meniscus is particularly prominent. Therefore, the design of professional knee protection should consider a reduction in landing impact with increased joint stability. Professional knee protectors can be effective in reducing the occurrence of sports injury and prolonging the career of athletes. The results of this simulation for three landing conditions provide a theoretical basis for the design of knee protection for freestyle skiing aerialists.  
Conceptualization, T.Y.; methodology, X.W.; formal analysis, Y.F.; writing--original draft preparation, Y.F.; writing--review and editing, T.Y. and X.W.; visualization, Y.F.; supervision, T.Y. and X.W.  
This research was funded by the Key Special Project of the National Key Research and Development Program \"Technical Winter Olympics\" (2018 YFF0300502) and the Natural Science Foundation Guide Project of Liaoning Province (2019-ZD-0517).  
The authors declare no conflict of interest.