The 3D Knee

I’m a big believer in the 3D knee. However, I remember when I was taught about the knee as a personal trainer and it was very much thought of as a hinge. This did’t change much through my training as a physio and still now I read a lot that almost ignores the knee in function and dismisses it as something that should be ‘held in line over the foot’.  Again this suggests that the knee is a single plane joint that can be consciously controlled.

Since watching Gary Grays DVD’s, ‘Chain Reaction Function’ I’ve been convinced in the 3D knee. Interestingly, we are taught to test the anatomical integrity of the knee in 3 planes. Testing ROM, ligaments, menisci, postero-lateral corner etc means testing in a 3 planes. However, all of this is done on the treatment table and none of it is done in function.

The thing that frustrated me when I was a personal trainer was that if the knee had full ROM, but had pain I was limited in what exercises I could do.  The if foam rolling, stretching and telling them to keep the knee tracking straight didn’t work…I was stuck! Something didn’t add up at all! It was a true lightbulb moment when Gary started explaining the knee in 3 planes.

Sagittal Plane

This is the one we all know and is the obvious one when you see the knee in function. I think it was John Hardy who described it as the show off plane of the joint. As with all joints there are 5 ways of achieving both flexion and extension. In gait it uses 1 way as a front foot (both moving in opposite directions) and another as a back foot (both femur and tibia anteriorly rotating, femur faster).

Frontal Plane

Here is where I really had a lot of learning to do.  Didn’t even think about this before.  As a front foot the knee will adduct and as a back foo the knee will abduct.

If we are talking about a right leg, as the foot hits the floor the knee will achieve abduction by the tibia tilting left and the femur tilting right.  For a back foot this process is reversed, creating the adduction at the back foot.

Transverse Plane

This one is even harder to see, but is no less important. There is very definite internal and external rotation at the knee.  Interestingly, as both a front foot and back foot the knee internally rotates, however, the way it achieves this is different for front and back.

If we use the right foot again for this example. As a front foot the knee achieves internal rotation via both the tibia and femur are rotating to the left, but the tibia is rotating faster = internal rotation.

As a back foot both the tibia and femur are rotating to the right, however, this time the femur is rotating faster = internal rotation.


This is a very brief introduction to the 3D knee, however, I really hope I have been able to demonstrate how the important it is to understand how the knee moves in 3D in function. The main advantage of this is that the assessment and treatment options you have are multiplied many times over. It makes finding ideal home exercises for your patients far easier and hopefully better outcomes are the result 🙂




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