Figure 1 Three-dimensional schematic diagram of the intact knee joint. A is left lateral view; B is anterior view; C is posterior view; D is right lateral view.

Figure 2 Three-dimensional schematic diagrams of the Ramp lesion classifications of the knee. A is partial superior tear as type Ⅱ; B is partial inferior tear as type Ⅲ; C is complete tear as type Ⅳ; D is double tear as type Ⅴ

Figure 3 Three-dimensional schematic of the loaded knee joint finite element model. A is mesh generation of the knee joint model; B is the knee joint model under applied load

Figure 4 Material properties of various knee joint structures

Figure 5 Schematic of knee joint model validation. A is schematic of stress distribution in ACL (anterior cruciate ligament); B is schematic of anterior displacement of the tibia; C is schematic of stress distribution in the intact meniscus; D is schematic of displacement in the intact meniscus

Figure 6 Contact stress and displacement at the meniscus ramp lesion site at zero degree of knee flexion under combined loading.Note: the knee model was subjected to a combined load of 1 150 N compression, 134 N posterior femoral force, and 4 Nm adduction force moment; the upper row is schematic diagram of the equivalent stress (von Mises stress) distribution; the lower row is schematic diagram of the total displacement vector field

Figure 7 Contact stress and displacement at the meniscus ramp lesion site under combined loading at 30° of knee flexionNote: the knee model was subjected to a combined load of 900 N compression, 134 N posterior femoral force, and 4 Nm adduction force moment；the upper row is schematic diagram of the equivalent stress (von Mises stress) distribution; the lower row is chematic diagram of the total displacement vector field

Figure 8 Contact stress and displacement at the meniscus ramp lesion site under combined loading at 60° of knee flexionNote: the knee model was subjected to a combined load of 600 N compression, 134 N posterior femoral force, and 4 Nm adduction moment；the upper row is schematic diagram of the equivalent stress (von Mises stress) distribution; the lower row is schematic diagram of the total displacement vector field

Figure 9 Contact stress and displacement at the meniscus ramp lesion site under combined loading at 90°of knee flexionNote: the knee model was subjected to a combined load of 300 N compression, 134 N posterior femoral force, and 4 Nm adduction moment；the upper row is schematic diagram of the equivalent stress (von Mises stress) distribution; the lower row is schematic diagram of the total displacement vector field

Figure 10 Effects of different loads and flexion angles on the maximum contact stress at the meniscal ramp lesion site

Figure 11 Effect of different loads and flexion angles on the maximum displacement at the the meniscal ramp lesion site