Defining the femur segments

You already have the origins for the two femur segments defined: LHJC and RHJC (see Defining the hip model). For the distal end, you need the knee joint centers. These are defined as the half-way point between the lateral and medial knee markers. You can then define the axes that define the femur segments:

1. On the Variables tab, with the CGM2.3 scheme selected, add a new variable named LKJC. Define this as a point halfway between LKNE and LKNM.
2. Repeat Step 1 for the right side.
3. Add a new vector named LFemurPD from point A=LKJC to point B=LHJC.
4. Add a new vector named LFemurML from point A=LKNE to point B=LKNM.
5. Use these two vectors to define the femur segment, which must be named L_Femur (to match the name of the segment in the VSK file). Add a new segment, name it L_Femur, select Origin A, Z-axis=B, X-Axis=BxC, then A=LHJC (remember, at the proximal end), B=LFemurPD and C=LFemurML.
6. Repeat Steps 3-5 for the right side to define R_Femur.
   Note that if you define the RFemurML from RKNE to RKNM, this vector points in the opposite direction (left) compared to the left side, which means that the R_Femur will have its Y-axis pointing right and its X-axis pointing backwards. To correct this, either use a factor -1 for the RFemurML in the R_Femur's specification, or flip the RFemurML vector itself. 

The following image shows the coordinate system of the R_Femur segment: