In an effort to convey a rather lengthy (and perhaps counter-intuitive) perspective, I generated three seperate posts on re-defining the joint. Although they essentially morph quite well into each other, they are spread across a number of months and therefore the message sometimes gets diffused or gets read in another order than the one intended. Therefore, I have decided to "amalgamate" all three into a single post...indeed, much longer but hopefully it results in a better flow of information and provides enhanced clarity.
Each on its own should provide some "food for thought", but as a whole I am hoping that the result is greater than the sum of all parts. Cheers!
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!
Re-defining The Joint: Part 2
This post is intended to supplement my earlier post "Re-defining The Joint: Part" and to continue the journey down the trans-anatomical road of discovery (or re-discovery, to be precise). If you haven't read part 1, I would recommend that you refer to that post before moving on with this one. It will certainly help in the understanding as well as give valuable insight as to what the main message is.
http://thescienceofphysicalrehabilitation.blogspot.com/2011/09/redefining-joint-part-1.html
To briefly summarize, I have proposed a revised definition of a "joint" as:
Linear and/or angular displacement between separate biological elements . This definition is more precise and accurate...but it also opens up an entirely new perspective on what actually constitutes a joint. As previously mentioned in my blog, connective tissue has 2 appearances which are seemingly paradoxical: it connects AND disconnects! The connection element is the obvious one (tendons, ligaments, joint capsules, etc) whereas the "disconnection" function is somewhat more counter-intuitive. If you haven't seen Gil Hedley's Integral Anatomy Series videos, then I highly recommend you make a point to watch them. Using standard dissection methods, he intelligently demonstrates the fundamental role of fascia (connective tissue) in SEPARATING body compartments, muscular groups, and systemic organs so that they do not mechanically influence each other. In essense, it allows the elements to "slide" against each other. For example, the liver "articulating" with the diaphragm, deep muscles of the hand (flexor digitorum profundus, for example) sliding underneath the more superficial muscles in the forearm when the fingers are flexed. It doesn't matter whether we actually agree on the definition of a joint...the reality is that without this fundamental characteristic, we would not be able to move...period. We would be as mobile and functional as a Ken (or Barbie) doll..."watered down" to simple hinge joints mixed with a couple of ball and socket joints for good measure.
Therefore, we must add to the understanding and definition of what a joint truly is. This will require some additional qualifying of the term "joint" when making statements or comments. We can consider our typical understanding of joints as SKELETAL ARTICULATIONS...because that's what they are. Therefore, I bring in a new term:
FASCIAL ARTICULATIONS.Each separate colour represents an individual fascial "compartment" and therefore can be considered as a separate biological element. This concept is easily extrapolated into the extremities as well...each individual muscle, muscle group, etc. is compartmentalized as well. It is important to remember that, when we are active (moving), these elements are articulating between each other! Consider a typical tennis swing...with its significant rotational components within the spine. There is a considerable angular displacement between the endothoracic fascia (fascia of the thorax) and the extended fascia of the abdomen (peritoneum). In addition, the follow-through of the arm at the completion of the swing is achievable through, not only the skeletal articulation, but the fascial articulations in the neck (deep, middle, superficial cervical fascia), the shoulder blade (endothoracic fascia), as well as the inter-muscular articulations.
Although it may be difficult to integrate "fascial articulations" into your mental hard drive, it should be easy to understand the obvious role of fascia in human movement...in both connection and disconnection. This provides a "bridge" to a more complete understanding of biomechanics...which is essentially the Trans-anatomical understanding of movement. Fascia is both friend and foe...when it is healthy and strong, you are feeling good. When it is damaged or otherwise unhealthy, it can be your worst enemy. From the most highly conditioned athlete to the the most severely affected child with Cerebral Palsy (who are near and dear to my heart), fascia is THE key fundamental structure in their health, maintenance, and development...period.
I hope the journey to date has been productive...and to those who are still "on the bus", part 3 will go into specifics about trans-anatomical movement and fascial articulations by using an age-old standard test (straight-leg lift) as an example. Hopefully it will engage and enlighten!
Cheers!
It has been quite awhile since the posting of part 1 and part 2, however there has been a recent ¨spike¨ in reads for both parts (currently rank #2 and #9 in the top 10 reads) therefore I think it is an appropriate time to complete the trilogy. As per part 1 and 2, a radical alteration of conceptual understanding of joints must take place in order to fully grasp (and appreciate) the complexity of human movement.
I read a book called The Structure of Scientific Revolutions that effectively demonstrates a ¨fatal¨ flaw in the evolution of science...most (if not all) of the new ¨scientific discoveries¨ are derived from already established paradigms. To be specific, research into human movement and (bio)mechanics assumes that the traditional mathematical model (single pivotal movement) is the ¨law¨...therefore every hypothesis, design, conclusion is derived from this ¨fact¨. Common sense dictates that, if the overriding paradigm is flawed (or otherwise over-simplified), then the results / conclusions will also be so. Although over-simplification has some merit in making treatment protocols easier to ¨digest¨and conform to current health care delivery methods, it does not mean than more precise and effective understanding should be ignored. In fact, deeper understanding does not disregard the current formula...rather it ABSORBS IT.
In order to fully appreciate part 3, I suggest a read (or re-read) of parts 1 and 2. However, to summarize the main message:
The true definition of a joint must be expanded into a broader understanding that it is the
linear or angular displacement between separate biological elements. Therefore, simple pivotal movement is only a fraction of the equation. There are 2 fundamental realities that also exist alongside of the classical mathematical model:
1) Fascial Articulations: This term defines the very real movement potential between the individual fascial layers that exist from the surface of the skin to the periosteum of the bone (and indeed even deeper into the very cell itself).
The above image illustrates an example of the fascial relationship between muscle/tendon and adjacent structures. Effective movement requires, not only proper ¨connective¨ elements, but selective ¨DISCONNECTIVE¨ properties. In other words, the ¨sliding¨ (hence articulation) of fascial layers between each other is essential. By definition, this constitutes a joint...without these characteristics, movement potential is significantly altered leading to movement dysfunction, irregualr load bearing and stress distribution, and ultimately deterioration.
2) Movement is more precisely ¨Gear-like¨: This is perhaps confusing and counter-intuitive, however it is none-the-less a reality. The pivotal model suggests that movement is a summation of single pivots moving at the same time. Once again, this is a serious over-simplification.
True function is achieved through a complex of gear-like movements that are NOT the sum of individual movements rather a single unified systemic response.
The image to the left clearly illustrates that single pivotal movement (hip joint) is effectively a small contributor to the performance of a straight leg raise (hip flexion). This movement is defined by gear-like movement between the individual vertebrae of the lumbar spine, the pelvis, and the hip. In addition, this requires proper fascial articulation (sliding) of the fascial layers of the posterior leg.
It is precisely these realities that highlight some of the current flaws in assessment and evaluation protocols. The fundamental question remmains: how can an effective treatment protocol be formulated when only one third of the mechanism is observed and identified??! At best, these types of approaches will be successful only 33% of the time and/or resolve only 33% of the initial problem. The concept of re-defining the definition of a joint only serves to enhance understanding and by default result in more effective interventions.
The switch from pivotal understanding to the ¨gear ratio¨ perspective will provide some valuable insight and clarity into the amazing movement potential of the human body. I am reminded of an ¨Old School¨ kids game called Spirograph. My brother and I played with this quite alot, but it has its merits from a conceptual perspective.
It involved placing variuos small gear-like tools into the center of a larger circle with gear teeth. You would then insert pencils of different colour into the smaller gear and spin it around the outer circle. The result was a myriad of amazing shapes and images.
Although it is a simplistic analogy, it reveals the sophistication and complexity that exists in this model...whch is reflected in the everyday marvel of human movement.
I hope this trilogy has been both informative and insightful. If nothing else, it serves as an example of the need to reach beyond current accepted paradigms in an effort to evolve your understanding.
Cheers.
