I am sure this is another one of your pop quizzes, so I will play along and answer more from a biomechanical perspective.
Awwwwww…. The poor knee. It just wants to be a stable fulcrum that allows the leg to be flexed and extended yet ends up being the meat in the dysfunction sandwich of the hip and foot/ankle complex. The knee really is in such a bad spot because it will be affected by what happens above and below if so much. I mean, if we get a foot that turns out we get a knee that is forced in, we get a hip that tilts up, we get a leg that will twist outwards. It just can’t win on is own.
With that being said, there may other links to knee pain. The most obvious omission to our list thus far is footwear. Raised heels are a no-no for sure. The muscles that makes up the back part of your lower leg are part of the plantar flexor group. The plantar flexors, along with the muscles of your thigh (rectus femoris) act as brakes when you walk. Walking is just controlled falling and it is the job of these two groups to control that motion. Raising your heel reduces the effectiveness of the brakes and places stress on the front part of the knee.
If we look at some of the other answers we can tie some of them together. For example, the anterior tilt of the pelvis, creates an internal rotation of the femur which creates the over pronation of the foot. But then question still needs to asked, “Why is the pelvis tilting and creating anterior tightness in the hip?” While there could be a number of reasons for this, it is certainly acceptable to to conclude that an uppercrossed syndrome could be creating the pelvic tilt and ultimately the knee pain.
So what does this all mean? Really, it means we can’t stop looking for clues when trying to determine the contributors to pain.
I really find NASM resources very helpful.
According to the National Academy of Sports Medicine’s, corrective exercise training manual, the following contribute to knee pain. (Chapter 13 – Corrective Strategies for Knee Impairment).
1. Knee valgus and varus
2. An increased Q-angle
3. Poor quadriceps and hamstring complex flexibility
4. Poor eccentric deceleration capabilities
5. Overtraining and playing on hard surfaces
6. Abnormal or dynamic lower-extremity malalignment
7. Altered muscle activation of surround knee musculature, decreased strength of the hip musculature
9. Abnormal gait or running mechanics
10. Weakness in the hip abductor muscles (gluteus medius)