Don't get me wrong, sometimes your knee can be the actual source of the problem, but it is most likely precipitated from somewhere else.
Where can that be. you might ask.
Two places: The Hip or The Foot.
Potentially both at the same time.
The knee is really comprised of two bones meeting, the femur and the tibia. The articulation between these two bones creates a relative turn that unlocks and locks the knee to allow for flexion and extension, respectively.
If the femur rotates inward (internal rotation) the tibia will be rotating outwards relative to it (external rotation), creating knee extension, aka the screwhome mechanism. The reverse happens for knee flexion where the femur externally rotates relative to the tibia internally rotating.
Starting by looking from the top down, we can see how a lack of femur rotation can affect the knee.
The femurs rotation really tells us the hips rotational ability. With that being said, a lack of internal rotation (IR) from the femur will cause a decreased ability to extend the knee, and a lack of external rotation (ER) would decrease the ability to flex the knee.
The same results can also occur if the tibia lacks the same rotational abilities, in this case, a lack of external rotation would decrease knee extension ability, and lack of internal rotation would decrease the ability to flex the knee. The tibia has it's rotational capabilities determined by the way the foot strikes the ground, just as the femur is a resultant of the hips' position.
As you can see, a resultant decrease in range of motion from the top or the bottom (and in some cases both), will leave the "middle man" (the knee) to have increased strain and pain.
There is an inability to transfer the forces up and down the lower extremity, giving us unwanted twists and torques at the knee joint.
Knee pain that is centered toward the inside of the knee is related to the loss of relative motions for knee flexion. The tibia is stuck in an increased external rotation as the foot strikes the ground, not allowing for tibial IR to occur. This means that the femur is not allowing enough relative ER to unlock the knee from up top either. As the knee bends, it is trying to bend from a "lock-out" position, thus straining the inside of the knee.
You will tend to see this in those with a high arch foot as this foot position biases the tibia to stay in more ER. This does not mean they automatically lack the capabilities to go thru a normal foot, ankle, knee, hip mechanics, just shows a bias.
With pain on the outside of the knee, you will see a greater lack of IR from the femur, preventing an ability to extend the knee well. It will have a stronger external rotation component from the tibia as an attempt to extend the knee, but the femur will follow it, causing a twist to compress the outside compartments of the knee.
For those with pain in the front of the knee, they tend to have flatter feet as it biases the tibia to IR and pushes the hip forward, causing your center of mass to be displaced more thru the knee joint. You may have a poor ability to extend the knee here as well, with potential to strain the patella tendon.
Now you can see how different components of the ability to rotate the joints above and below the knee can influence it's ability to move and change how forces are distributed amongst the joint itself.
Clearly there is not one way to fix this, but the best start is to see how well things move up top first, then work towards establishing your motions below.
Perhaps you are "stuck" in knee flexion or extension and don't know where to start.
We can always have a quick chat on the phone and I can guide you through some steps to get started.
If that sounds like something for you, click the button below.
Dr. Peter Dionisopoulos is the owner and founder of Dynamic Performance & Rehab. He has a Doctorate in Physical Therapy and enjoys to help active adults maintain their lifestyle and provide natural solutions to their pain.