Post 82: how the disc moves

How does the disc move?
“Clinically, disc herniation is most commonly observed posteriorly or posterior-laterally”

Very rarely does the disc herniated straight backwards (posteriorly). There is a very strong ligament at the back side of the spine that prevents a posterior herniation. The material in the disc will typically make a trough in the disc and go sideways from that point.

“Specifically, when the spine is loaded asymmetrically, the nucleus tracks along a radial fissure formed in the contralateral corner of the disc suggesting that annular delamination is load/direction dependent.”
 When the spine is loaded asymmetrically is similar to bending sideways. Picture the spine as a bunch of books loaded on top of each other with big bars of wet soap in between. When you bend to the right, you would bring the right sided edges of the books closer together (i.e. they would be compressed) and the left side of the books would be gaped open (i.e. they would decompress). If there is a wet bar of soap in the middle, it would move away from the compressed side. This is what the above sentence is saying in a lot of words. There is more to it than this, such as forming a trough, which is similar to the annular fissure.

The disc is composed of two separate parts: the annular rings and the nucleus. The annular rings are a cartilaginous protector of the nucleus. It’s similar to putting Play Do in a sealed freezer bag. When you push on one end of the freezer bag, the play do goes in the opposite direction. This holds true for most discs. There is a study (I have trouble remembering the name, but its by a Japanese author…I’ll try to find it and write a post on it) that demonstrates that as the discs age and dehydrate, they may not always move away from the compressed side, but this is a different story for a different day. Just know that for the most part, most discs operate like this on most days.

“Callaghan and McGill (2001) determined that posterior disc herniations are consistently created with repetitive flexion under modest static compressive forces”

McGill…Oh great guru of spines…has done much research regarding the biomechanics of the spine. Stu, as he likes to be called, is actually very approachable and responsive to e-mails, which is surprising considering how high profile he actually is in the rehab world. Anywho…what they found was that a disc herniation is predictable with specific forces. If one repeatedly bends forward while standing and does this bending from the spine (NO-NO) instead of from the hips.

“Their data suggests that disc herniations are an injury that result from cumulative bending trauma and can initiate after only 5870 cycles of flexion/extension while under a compressive load of only 867N.”

It’s funny that they use the term “only 5870 cycles”. That’s a whole heck of a lot of flexion/extension cycles. This is more of the case of the straw that broke the camel’s back more so than one cycle of flexion/extension. The number that the authors gave for force is equivalent to about 200 pounds. Now take your upper body weight plus any external weight and this is the number of flexion cycles that it would take to cause a herniation.

“Bending the motion segments about an axis oriented 30 (degrees) to the left of the sagittal plane flexion axis resulted in the focused nucleus tracking toward the posterior right side of the disc in 15 of the 16 trials”

What this means is that in a majority of people, bending towards one direction will cause a movement of the disc material in the opposite direction. The are treatment strategies that are based on this exact theory.

“Discovering that the side that the nucleus tracks is dependent upon the direction of bending motion is of use in understanding injury mechanics”
This means that we could reverse engineer the injury if we have a picture of the disc. It also means that we could reverse the injury if the disc is still intact by moving in the opposite direction of the problematic motion. These are theories of course, but this type of theory is used in treatment.

NOTE: This article uses a porcine disc model, which is commonly used in the research to mimic the motion of the human disc.

Excerpts from:

Aultman CD, Scannell J, McGill SM. The direction of progressive herniation in porcine spine motion segments is influenced by the orientation of the bending axis. Clinical Biomechanics. 2005;20:126-129.

Author: Dr. Vince Gutierrez, PT, cert. MDT

After having dedicated 8 years to growing my knowledge regarding the profession of physical therapy, it seems only fitting that I join the social media world in order to spread a little of the knowledge that I have gained over the years. This by no means is meant to act in place of a one-one medical consultation, but only to supplement your baseline knowledge in which to choose a practitioner for your problem. Having completed a Master of Physical Therapy degree, the MDT (Mechanical Diagnosis and Therapy) certification and currently finishing a post-graduate doctorate degree, I have spent the previous 12 years in some sort of post-baccalalaureate study. Hopefully the reader finds the information insightful and uses the information in order to make more informed healthcare decisions. MISSION STATEMENT: My personal mission statement is as follows: As a professional, I will provide a thorough assessment of your clinical presentation and symptoms in order to determine both the provocative and relieving positions and movements. The assessment process and ensuing treatment will be based on current and relevant evidence. Furthermore, I will educate the patients regarding their symptoms and their likelihood of improving with either skilled therapy, an independent exercise program, spontaneous recovery or if the patient should be referred to a separate specialist to possibly provide a more rapid resolution of symptoms. Respecting the patient’s limited resources is important and I will provide an accurate overview of the prognosis within 7 visits, again based on current research. My goal is to empower the patient in order to take charge of both the symptomatic resolution and return to full function with as little dependence on the therapist as possible. Personally, I strive to be an example for family and friends. My goal is to demonstrate that success is not a byproduct of situations, but a series of choices and actions. I will mentor those, in any way possible, that are having difficulty with the choices and actions for success. I will continue to honor my family’s “blue-collar” roots by working to excel at my chosen career and life situations. I choose to be a leader of example, and not words, all the while reducing negativity in my life. I began working towards the professional aspect of the mission statement while still in physical therapy school. By choosing an internship that emphasized patient care and empowering the patient, instead of the internship that was either closest to home or where I knew that I would have the easiest road to graduation, I took the first step towards learning how to utilize the evidence to teach patients how to reduce their symptoms. I continued this process by completing Mechanical Diagnosis and Therapy courses A-D and passing the credentialing exam. I will continue to pursue my clinical education through CEU’s on MDT and my goal is to obtain the status of Diplomat of MDT. Returning back to school for the t-DPT was a major decision for me, as resources (i.e. time and money) are limited. My choice was between saving money for the Dip MDT course (about 15,000 dollars) and continuing on with the Fellowship of American Academy of Orthopedic Manual Physical Therapists (FAAOMPT) (about 5,000 dollars), as these courses are paired through the MDT curriculum or returning to school to work towards a Doctorate of Physical Therapy degree. I initially planned on saving for the Dip MDT and FAAOMPT, but life changes forced me to re-evaluate my situation. The decision then changed to return for the tDPT, as my employer paid for a portion of the DPT program. My goal for applying to and finishing the Dip MDT and FAAOMPT is 10 years. This is how long I anticipate that it will take to finish paying student loans and save for both programs, based on the current rate of payment. I don’t know if I will ever accomplish what I set forth in the mission statement, but I do know that it will be a forever struggle to maintain this standard that I set for myself.

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