Spinal Mechanics

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It used to be thought that muscles alone were the sole driving force for spinal articulation. ‘Spinal articulation’ is the technical name for how the joints move against each other. Bayliss elaborated on this in his synergetic theories, summarised below.


Two powerful opposing forces.

The way the spinal and sacroiliac joints articulate can be be likened to the mechanism of a grandfather clock. At the lower end, the pelvis acts as a pendulum and swings the pelvis from side to side under weight-bearing conditions. At the upper end between the ears, the centre of balance uses muscle energy to keep us upright. See figure 1.


The vertebrae nearest to the pelvis are forced to move in the the direction of the pendulum arc while the vertebrae above and nearer to the centre of balance are forced to counter this force in order to keep the person upright.


Clever and very efficient.

These opposite forces appose each other at every joint in the spinal column and within the sacroiliac joints. Each and every joint therefore encounters a shearing force that passes horizontally through it. See figure 2. When harnessed by supporting muscles and ligaments, this shearing force becomes a very powerful and efficient driving force.  The local bony shape of the two articulating vertebrae determine the angle and trajectory each every joint makes.


Try this test out for yourself. Stand with your level feet a few inches apart and relax. Side-shift your pelvis to the right. Notice that all your body weight is being taken on the right side of your pelvis and hip and that your left leg has become marginally less weight bearing. Also note that your spine/body have naturally rotated to the right.   This rotation occurred naturally without you having to actively engage any of your torso muscles.  


Observe the lady’s lesioned pelvis in figure 3. In particular, look at the angle of her pelvis at rest and the oblique trajectory that her pelvis would follow during its pendulum arc. Common sense tells you that the modified arc is going to cause trajectory problems within each joint above and between.  Although the actual mechanism is more complicated, this is what causes joints to lock against each other. This locking in essence is what Osteopaths call an Osteopathic lesion. A lesioned joint is ‘locked energy’ and is often painful when palpated (pressed) and can affect the blood supply to the nerves, muscles, torso, legs, arms and in some cases the organs of the body.


Where can I find more information on synergetic spinal bio-mechanics?

The exact mechanism for how the whole spine articulates synergistically and how lesions are created is detailed in John Bayliss’s latest book ‘Advanced Osteopathic Technique’


Why see a PPT Osteopath.  

In every session, due to the low trauma footprint of PPT manipulations a PPT Osteopath will set out to correct the alignment of every spinal joint and lesion in the spine and pelvis. This sets a new standard in osteopathic excellence. Before and after.


Why would anyone want to correct the alignment of the whole spine?

If we liken the spine to a tent pole and the supporting muscles as its guy ropes, we would see a picture similar to figure 4 below. Now if we add the osteopathic lesions that are commonly found in the spine, the tent pole and the guy ropes would look like figure 5 below.


Imagine trying to correct the alignment of the tent pole in a three dimension way by tightening and loosening the guy ropes to make that fixedly bent tent pole straight. It would be a nightmare with little to no chance of success.  


Why is it so important that the pelvis and vertebrae are in alignment?  

Vertebrae are designed to house and protect the spinal cord which is the body’s nerve highway. Each lesioned joint in some way meanders and diverts the nerve pathway and in some way hampers the flow of nerve energy passing up and down its length. Osteopathic lesions and this interruption to energy flow can cause joint and muscle pain, nerve pains and underlying nerve conditions that can in many cases lead to an assortment of health problems in later life.











How the spine Articulates

Figure 1 Grandfather clock

Figure 2  Graded movement

Figure 3  lesioned back

Figure 4  Tent pole spine

Figure 5  Tent pole lesioned spine

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