What is a Disc Injury? Misconceptions And Myths surrounding Low-Back Injuries
You may have overheard a coworker, family member or friend off-handedly remark that she has a ‘slipped disc’ or he has ‘put my back out.’ However, what exactly does this mean?
80% of Canadians will suffer low-back pain at least once during their lifetime1 The incidence of back injuries is equally reported between both males and females2 Low back-pain is the most disabling musculoskeletal condition3. Indeed, the WHO stipulates that chronic low-back injuries have the highest level of disability costs. These costs include lost hours of work, increased medicare costs, increased social services costs and loss of quality of life. It is estimated that the Canadian medical system will spend anywhere between 6-12 billion dollars annually on costs related to low-back pain4. Furthermore, low-back injuries are often mismanaged because 66-72% of people will experience a recurrence of low-back pain within twelve months of their initial injury.56
As a physiotherapist with fifteen years of clinical experience, 50-80% of my weekly caseload is comprised of patients with back injuries. So, what exactly are people referring to when they remark that they’ve ‘slipped a disc’? Clinically, they are referring to a disc derangement or a disc injury.
Disc derangements are divided into two categories:
a) Disc Protrusion: slight protrusion of the outer ring of the disc (annulus fibrosis) into the spinal canal. Part of the annulus fibrosis may come into contact with the lumbar spine nerve roots, producing neurological compromise.
b) Disc Herniation: extrusion of both the outer ring of the disc and the inner portion of the disc (nucleus pulposus) into the spinal canal. Neurological impairment occur if the disc impinges on the adjacent spinal cord or lower extremity nerve roots. This can entail abnormal sensation in the legs, loss of bowel and bladder control. If conservative methods fail, surgical intervention is warranted.
The adult human spine is comprised of 33 vertebrae. These are organized into five sections; the cervical spine, the thoracic spine, the lumbar spine the sacrum and the coccyx. The former three segments are comprised of vertebrae that are inherently designed to move. The latter two segments are comprised of nine joints which are fused and thus, are inflexible.
Disc instability can occur in any part of the lumbar, cervical or thoracic spine. However disc injuries most commonly occur in both the cervical and lumbar spine. With respect to the lumbar spine, it is the weakest part of the body, which renders it the most susceptible to injury.
To resist these gravitational forces the lumbar spine is encapsulated by a matrix of superficial muscles, stabilizing muscles, cartilage and ligaments. These structures serve to protect the internal organs, vertebrae, vertebral discs, spinal cord and spinal nerves.
Age, occupation and lifestyle choices (including sedentary lifestyles) cause erosion of the structures of the spine. Specifically, the cartilage between the vertebrae erodes, the canals through which the spinal nerves traverse narrow (due to deposition of osteophytes), ligaments lose their integrity, the discs lose their fluid (vertebral discs are primarily composed of water and collagen) and the stabilizing muscles weaken. Unlike muscles, ligaments can not be strengthened. They do not have the same contractile properties and vascularization of muscles. Hence, once they lose significantly lose their integrity, it can’t be restored. The loss of ligamentous integrity is a primary culprit for a lumbar disc injury.
Contrary to common belief, degenerative changes in the spine start in the second decade of life. Indeed, a study examining the MRI scans of the lumbar spine of persons 20-22 years old revealed that 48% of these people had degenerative disc disease and 20% of these people exhibited disc protrusions Moreover, another study of individuals under thirty years old revealed that over 40% of these people’s MRIs exhibited degenerative changes in their lumbar spine7. Hence, I have treated numerous young adults with back injuries, including lumbar disc derangements.
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