So why is it that 80% of people at some point will experience low back pain? Is it that we were never meant to evolve from knuckle dragging or is there a better reason? The answer to this question has more to do with common sense than with evolution. What do you think would happen to your car if you didn’t put oil in the engine? Common sense. Right? So why is it difficult for some people to understand the importance that proper posture, body mechanics and exercise play in spinal disorders such as neck and low back pain, herniated discs, and sciatica? Let me explain.
First, let’s think of the discs in between your vertebrae as water balloons. When you squeeze one side of the balloon, the fluid will move in exactly the opposite direction. Right? However, physics tells us that when a pressure is exerted on a closed system, the pressure is equal in all directions . This would be true for a “healthy” system. So, yes, when the disc is healthy and strong, the pressure exerted on the disc is the same in every direction. However, what if one of the “walls” of the system is weaker due to chronic overuse and microtrauma? Think about the daily sloucher at the computer.
The more we are slumped, or flexed forward, the more stress that occurs to the back part of the disc. Remember, if we pinch the front, the fluid moves toward the back. In this regard, evolution is cruel, because the back part of the disc is the thinnest and the most susceptible to trauma. Bingo! The origins of a bulging disc. Why is it that some people with low back pain have an MRI and it doesn’t show a bulging disc? Oh, and by the way, radiologists use the terms “bulging”, “herniated”, and “protruded” interchangeably. Some even go as far as saying “there is bulging, but no herniation”. Huh? The proper medical terms would be protrusion, extrusion, and sequestration. I hope you’re not totally confused now! So what if the radiologist report says “only mild bulging” of the disc? Does this mean that the disc is definitely not the origin of the pain? Absolutely not! Although there is no clear relationship between the extent of disc protrusion and the degree of clinical symptoms, the periphery or annulus fibrosis of the disc is highly innervated. In fact, Bogduk in 1981 reported that “nerve fibres were found up to a depth equivalent to one third of the total thickness of the anulus fibrosus”. Edgar in 2008 confirmed this deep penetration of sensory nerves into the disc. Therefore, any trauma or even “mild bulging” to the peripheral layers of the disc could elicit pain. Kuslich confirmed that probing and electrical stimulation to the annular fibers could produce local LBP, but not leg pain. However, Ohnmeiss discovered that partial or full thickness anular tears, with or without disc bulging/herniation, can reproduce sciatica symptoms in about 60% of properly screened patients with chronic lower back pain . So then, what is sciatica? It is referred pain down your leg from a pinched or irritated nerve or from a traumatized disc or facet joint. The facet joints are the “winglike” structures in the picture below and, as you can see, the spinal nerves exit the spinal canal right next to the disc. Hersch showed that injection of an “irritant” such as saline into the facet joints of the spine can cause LBP. In addition, McCallwas able to reproduce sciatic symptoms with facet joint injections. It has also been well documented that a protruded disc can cause a “pinched nerve” and associated sciatic symptoms. Ouch!
So what does all this evidence mean for you? It means that the source of your low back pain is not always definitive. It can be multifaceted. In most cases, a thorough physical therapy evaluation will determine your neural sensitivities and functional impairments. Common sense tells us that avoiding postural stresses will place the body in an optimal position to heal. Appropriate manual therapy such as joint & soft tissue mobilization and manual traction as well as evidence-based spinal stabilization exercises should alleviate and prevent reoccurrence of symptoms. These will be the topics of the next two blog posts. So stay tuned!