Initial orientation to 0 flexion

This step moves the femur from it’s initial position to 0 degrees flexion. The femur’s flexion angle is controlled, and is free to move in other degrees of freedom. There is a nominal 20 N compressive load applied to the femur throughout this step.

Interactions

The orientation of the knee at the end of this step is orientation at the beginning of the passive flexion test. As such, all of the interactions that are desired for the passive flexion test are active during this step. These interactions are still active from the previous steps.

Kinematic Boundary Conditions

Femur

For the passive flexion test, the femur will be unconstrained in all directions except for rotation about the flexion axis. The angle about the femur’s flexion axis will be assigned throughout this step.

The initial orientation of the knee is known after the femur and tibia coordinate systems are defined with respect to the MR image’s coordinate system (more details in Coordinate Systems). The initial flexion angle is used to define the kinematic boundary condition for the femur during the initial step. The rotation is applied to the connector element that corresponds to the flexion axis.

  • Change the flexion from the initial value to zero
    • The femur is free to move in other degrees of freedom

Tibia

The tibia will be fixed in all degrees of freedom.

Patella

No kinematic boundary conditions are applied to the patella or the quadriceps tendon.

Kinetic Boundary Conditions

Femur

To reduce the instability in the simulation, a nominal 20 Ncompressive force will be applied to the femur during this step. This force will be applied to the connector element that corresponds to the SI axis. No other external forces will be applied to the femur.

Tibia

No external loads are applied to the tibia in this step.

Patella

To reduce the potential for instability, a 20 N load is applied to the patellar quadriceps connector element. This load is maintained at 20 N throughout this step.