“Tribology is defined as the study of the mechanisms of friction, lubrication, and wear of interacting surfaces that are in relative motion. Based on the similarities of biomechanical and mechanical systems, the premise for insuring the efficiency and longevity of the components of the human movement system is maintaining precise movement of rotating segments.” – Shirley A. Sahrmann, PhD, PT
(Biomechanics)
Your knee joint is a bi-axial synovial joint.
*You* and I have two invisible lines that run through our knees. They are referred to as axes in a biomechanics lab or class.
You can attend a biomechanics class at a university anywhere in the world, and the professor will tell you that you have a horizontal axis that runs from the inside of your knee to the outside of your knee, e.g., A mediolateral (fronto-horizontal) axis.
(Principles)
The other axis at your knee is vertical *and* it allows for rotation of your lower leg at the knee joint.
The same vertical axis allows for rotation of your femur at the knee joint.
At the same time that your femur is rotating at your knee joint; the other end of the bone is also rotating at your hip joint around an invisible vertical axis.
While your femur is rotating at the knee *and* the hip joint; your pelvis is also rotating on your femur at the same joint.
*All* of the motion and much more is driven by your foot as the forefoot/midfoot makes contact with planet Earth.
*Right* below your ankle joint, you have a joint that is formed by the meeting of two bones called the talus and calcaneus (heel).
Your talus sits on top of your heel and these two distinctive bones make-up the very unique *and* extremely important subtalar joint.
(Priorities)
The joints throughout your big toe (1st ray) are the only joints that are functionally more important than your subtalar joint.
If you don’t have a subtalar joint that allows for normal (natural) motion, range of motion at your knee will be limited.
A restriction in range of motion at the knee does not allow you to be an efficient shock absorber on each *and* every single leg landing.
*Running* (not walking) is a series of single leg landings.
(Proprioception)
The mechanoreceptors in and around your knee love to reach the extremes of joint motion in all three planes, e.g., Abduction of your lower leg at the knee joint.
Your knee is reacting to your foot, and your hip is responding to your knee (and foot!) .
At the same time that your pelvis (hip) is reacting to your knee, your spine is responding to motion of your pelvis, your cranium is reacting to the motion of your cervical spine, and your temporomandibular joint (jaw) is driven by your cranium, which is resting on the top of your spine.
*Everything* is connected in more ways than one. (emphasis added)
Asking a different question.
It is very unproductive to look at pain and degenerative changes at the knee without first exploring the mechanics of the foot *and* hip, e.g., Runners Knee.
If you limit motion throughout the support (foundation) system; you limit motion throughout the chain.
(Curiosity)
Think of it like a recipe that you are following in the kitchen:
Leave out one ingredient (a component part) and the end result is altered considerably.
(Perspective)
