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Understanding mechanisms for injury

The spine and discs move in opposite directions. Understanding this we can see how movements can lead to a disc injury.

The amount of movement that takes place at the spinal segments is different throughout the spine. Most loading passing through the spine is around the level of L4/L5; this is where most movement and spinal pathologies take place. We need to ensure when we give a movement there is proper load transfer; otherwise people injure their lower back.

The orthopedic profile perspective determines the technique demands of a move or lift for that person, to understand what led to injury through training. If the client does not have the orthopedic profile for the lift or move injury is created through poor load transfer.

The vertebra is a 3-joint complex; 1 inter-vertebral disc with 2 facet joints, in which the disc is designed to deal with most of the loading. In a healthy spine as weight passes through the vertebrae, 84% passes through the disc; 8% through each facet joint.

When it comes to the intravertebral disc, the viscous material in the middle is the nucleus propulsus and the network of collagen fiber layers around it is the annulus fibrosis. It follows what is known as Pascal’s Law, meaning that the pressure that passes through the disc will be distributed evenly throughout the annular fibers.

The pressure radiates in all directions and it is the function of the annulus to maintain this. Cumulative stresses on the annular fibers begin to break, or no longer fully contain the nuclear material.

The viscous material of the nucleus is much like phlegm. Imagine spitting phlegm into a tissue and wrapping the tissue around it; this would be the nucleus with one annular fiber layer; now wrap 16-20 more tissues around it, here we have an easy visualization of a disc. The 16-20 layers of annular fibers have an alternating oblique orientation of 45 degrees, alternating right, then left.

This alternating pattern offers resistance in flexion, extension and rotation. Rotation is vulnerable because half the annular fibers are aligned in the direction of rotation; the other half are not.

This is why we hear that rotation can be damaging to the lumbar spine.The Nachemson Intradiscal Pressure model shows that when standing the intradiscal pressures are at 100% and when sitting the pressure rises to 140%. The most common disc bulge is posterior lateral and is aggravated by repeated bouts of flexion.

When someone has low back pain, often yoga is the first thing that comes to mind.

The repeated bouts of flexion in yoga can aggravate the disc bulge, depending on the stage.

As we bend forward from standing the intradiscal pressures rise from 150-200%; when seated and bent forward it can range from 185-375%. The nuclear material moves in the opposite direction to the spine. Bending forward the disc goes back; bending right the disc goes left, etc... Moving into extension the disc goes forward and pressure goes down, this can centralize the disc material.

A high percentage of people who have a disc derangement one (DD1), the most basic stage, don’t even know it. The reason is, only the inner layers are breached; here there are no pain sensitive nerves. The disc pressure is so high on the inside that free nerve endings cannot survive, the neural input is only around the outer third of the annulus.

A Prolapse is when the outer third of the annular layers are breached. The central canal runs behind the discs and when they start pressing up against the spinal cord this can cause serious issues. The spinal cord is much like a hose and at the level L1 or L2 it branches off into different nerves, resembling a horse’s tail called caudia equine. A sign of caudia equine syndrome is saddle anesthesia, a serious problem. Imagine you’re sitting on a horse’s saddle and the parts of your body that are in contact with the saddle go numb.

If a client talks about urinary or bowel incontinence, this can be a sign of a disc bulge in the central canal, they may need surgery. The body is trying to protect the caudia equine, this is why posterior lateral is the most common direction for the disc bulge. Sitting laterally is the neural foramen, which is an exit canal where the nerve root will come out.

The disc bulge begins takes up space in the neural foramina and meets the nerve root coming out. As the nerve root is compressed, pain increases and migrates down the leg with a lateral shift. Clients with a lateral shift while standing will show the shoulders moving to the right or left to get away from pain, if the disc bulge is above the nerve root, they lean away from it to pull the nerve root away from the disc for relief.

If the disc bulge is below, they will shift to the same side as the disc bulge. Disc derangement classifications are based on whether or not a lateral shift is present and how far the pain has migrated.

In each derangement stage there is a loss of disc height as well as loss of tension of the spinal ligaments, resulting in segmental instability. DD1: a small posterior disc bulge; lower back posture becomes flat; localized pain; will respond well to yoga. DD2: disc has bulged to the central canal; can get caudia equine; no lateral shift; lumbar kyphosis and Yoga is no longer ideal; DD3: no lateral shift; pain can be localized in the lower back, buttocks, hamstrings but has not gone below the knees.DD4: lateral shift present; there is pain to the kneeDD5: no lateral shift; pain has migrated to the foot. DD6: lateral shift present; pain has gone to the footDD7: complete opposite and rare, about 6% of the time; disc bulge is anteriorExcursion is when the nuclear material has breached the outer layers of the annulus. This acid-like material will burn whatever it touches causing compressive type symptoms and inflammation.

The nerve root has sensory, motor and autonomic characteristics. With a mild disc bulge, there is some compression on the nerve root, creating sensation changes. As the compression gets worse the motor consequences are muscle weakness. With a massive compression on the nerve root there can be autonomic consequences. A nerve that innervates a muscle has atrophic function, meaning it sustains the function and health of that muscle.

There are different proteins that travel down a nerve which nourish the muscle. If this flow is disrupted the muscle starves and atrophy begins.

Finally, we come to the worst one, which is Sequestration, this is not only the disc bursting out through the outer layers of the annulus but disc fragments have broken free and are floating around in the epidural space as well, causing severe pain, this requires surgery. There is no such thing as a ‘slipped disc’ -- that is a misnomer; only these disc situations occur.


Mark Buckley: FMA Strength Training

Porterfield, James A.: Mechanical Low Back Pain Perspectives in Functional Anatomy

Paul Chek: CHEK Practitioner Level 1 Manual

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