Thursday, September 15, 2011
Redefining the Joint: Part 1
Why in the world would I suggest that the word "joint" be re-defined? It's a simple thing, right? Let's look at the definition as quoted in the Merriam-Webster Dictionary: the point of contact between elements of an animal skeleton with the parts that surround and support it . This definition conjures up the image that likely popped up in your mind...2 bones, some soft tissue around it, and maybe a meniscus in between.
The above image is nothing new to anyone. You have the pivot joint, the ball-and-socket joint, and the infamous hinge joint. This image follows the quoted definition quite nicely. The unfortunate thing is that the mechanics of human movement cannot be compacted into a simple definition and certainly not be explained by simple mathematical models. "Well, what is the right definition then?"...I would be naive to suggest that this definition is "wrong" per se, rather I merely suggest that it is very simplistic. Complex systems, by definition, demand complex explanation and understanding...therefore a more global perspective is required. As per "Gavin's New Trans-anatomical Dictionary", a joint is defined as: Linear and/or angular displacement between separate biological elements . To many of you, this may seem like a fancier way of saying the same thing...however, you couldn't be further from the truth. The reality is that the skeleton (bones) has a "monopoly" on everything joint-related. Why is this so?...by convention! It's in the dictionary, Gavin. But if you look at my definition, the skeleton is only a PART of it. Linear and/or angular displacement indeed occurs at all of the "typical" spots you would think of (knees, elbows, shoulders, etc)...however, if linear and/or angular displacement is a key element in this definition, you need to consider EVERY area that experiences this displacement as a true joint!!
It is not sufficient to suggest that movement only occurs at the "joints" and the soft tissue is simply a "biological sleeve" that fit over it. It clearly involves sliding of specific fascial layers one on top of the other. For example, the tendons of the wrist actively slide against each other when activated...which, by definition constitutes a joint. As you flex your arms, the fascial layers (from the skin to the triceps) on the back of the arm slide against each other and along the humerus...this constitutes a joint. The fundamental question is: who decides that if there is no bone, there is no joint?". If you consider the scenario where these movements are restrictied or blocked (fascial layers are "glued" together), you would have NO PRODUCTIVE MOVEMENT AT ALL. Therefore, when you consider this fact, the whole idea of "assessing range of motion" becomes something quite daunting...and perhaps even seemingly impossible. We therefore come to a crossroad of sorts. You can either go one way down "Newtonian Anatomical Model Boulevard" and be quite happy and comfortable with the status quo (which is a completely acceptable decision)...or you can go the other way and travel on "Trans-Anatomical Model Road" and walk a path of some unknowns and new discoveries.
I will go into more detail on the transanatomical definition of movement in part 2. For now, i will let you pause at the "crossroad"...digest the concept...and for all of you who choose Transanatomical Road, see you around the corner!