The Wondrous Joint
I hope it is not a disappointment that this article is about anatomy and not an intoxicant.
Every aspect of human anatomy and physiology incites wonderment. In fact, the more you know about how our human body works, the more astounding our entire structure and functions are. If asked to pick a favorite part most chose the nerve-enriched pleasure centers – lips, taste buds, eyes, ears and other more private sensory pleasing areas.
Frankly, for me nothing beats the knee. Don’t get me wrong, I am as fond of sensory delights as the next person. However, from the anatomic and physiological point of view those functions are not really that interesting, clever or awe-inspiring. To experience jaw-dropping amazement, the knee wins hands down every time.
It is so common to take our knees for granted that I doubt many could describe the entirety of the knee’s work. Only after the knee begins to fail in its functions, might a person take notice. Even then it is unlikely that what the knee does could be described in detail.
What is so special about the knee? It has to perform an impossible task, which it does with an astute cleverness that obliges respect. Here is the knee’s assignment, or rather its dilemma. The knee must provide flexibility to the leg so that it can bend, allowing walking, running, climbing stairs and stooping. At the same time, it must provide stability so that the leg is consistently weight-bearing, secure, strong and immobile. In short, the knee must bend but stay immobile, be stable while being flexible. A difficult dilemma indeed.
Despite this paradoxical set of goals, the structure of the knee appears basic enough, even surprisingly elegant in the simplicity of its design. The knee is made up of complementary shaped bone ends, the tibia and the femur, padded only with two crescent shaped pieces of cartilage and then all linked together by four strands of ligaments. With these basic ingredients, the knee holds us straight and bent, stable and flexed while making smooth transitions from one state to the next.
Did you ever wonder how the knee holds together when you climb stairs? Consider this: when climbing there is a point when you are swinging your lower leg up to place it on the next step above. Of the leg still holding you in place, the knee is bent and changing angles while supporting your entire weight. In fact the vector of forces makes the strain on the bent knee more than your actual weight. Why don’t the two bones comprising the knee slip apart under the strain? Conversely, why does a knee strong enough to hold together on the stairs allow such flexibility of movement in the first place?
Running is another good example. When running, the leg brought in front makes contact with the road. As the foot touches the ground, the bent front knee takes the impact. With such impacting force, why doesn’t the femur bone of the knee slip off the lower leg bone, the tibia? The next motion of that leg is the knee straightening in a spring-like action to create enough force to propel the runner forward. The knee must have enough strength to stay stable during this motion and propulsion. Amazing isn’t it!
The knee is miraculously designed for both flexibility and stability, with the ability to modulate between the two states. Sometimes more stability and strength are needed, while other times more flexibility and bending is required. The knee provides just the right amount of each, given what the ever-changing situation requires. Too much of one or the other would derail what we are doing, causing damage, injury or other problems. Even for knees, “to everything there is a season and a time to every purpose under heaven.”
Wait, there’s more! Not only does the knee perform these dual and contrasting functions with ease and grace, it provides us with a model to emulate. We humans are also designed for both flexibly and stability. There are times when we should be firm, resolute and unbending, such as a parent must be when a child wants to do something dangerous. Other times, it is imperative to be flexible, moveable and adaptable, such as when learning something entirely new. There are times when more stability and strength are needed, while other times more flexibility and bending is required. Many situations call for a particular blend of steadfastness and changeability, proportions that also may change as the situation changes. The healthy, mature person is able to apply just the right amount of each, given what is required. In fact, one part of the definition of health is having just that ability.
Conversely, when a person is too firm we call them dogmatic, uncompromising or stubborn. If they are too accommodating, we call them gullible, impressionable or naive. Residing on either extreme end of the spectrum is a recipe for pathology and a variety of difficulties of functioning in life.
We should all be like our knees, those models of flexible stability and steadfast yielding. We should all bend when bending is called for and be resolute when that is called for and have the wisdom to know the difference.
Linda Johnston, MD
© 2016 Linda Johnston, MD