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Low Back Pain

Why is it Important? 

The occurrence of low back pain has been recorded for thousands of years but the rate of incidence has increased in modern times faster than the rate of population growth and treatment costs have increased faster than the rate of inflation. 

In the United States back problems have become the second biggest reason for missed work at a cost of between 30 and 80 billion dollars a year including the cost of lost productivity. It is known that 90% of all Americans will experience a disabling episode of low back pain at some time in our lives and 50% to 70% of the adult population experience repeated episodes of low back pain over the course of a lifetime. At an average cost of approximately $7,400 back problems are the number one disability for people under the age of 45 according to the Society of Prospective Medicine Directory of Health Risk Appraisals.  

Industrialized countries consistently report a higher rate of low back pain and disability with the prevalence estimated to be nearly 70%. In addition, European studies have concluded that 60% of schoolchildren experience back problems by ages of 15 or 16. 

Who Gets Low Back Pain? 

Men tend to have a higher incidence of low back pain than women between the ages of 25 and 55 after which the incidence for men drops off. For women the rate increase increases beyond 50 years. One study in England found the incidence increased until the sixth decade then declined after age 70. The first episode occurred before 65 in 75% of the subjects.

It is unfortunate that many of the objective findings that show up on diagnostic tests are poor predictors of who will experience future episodes of low back pain. In fact many people who are without pain have osteoarthritis of the spine or bulging or herniated discs. One major study came up with only two reliable predictors for the likelihood of future back pain. One was a past history of back pain and the other was a history of cigarette smoking. 

Prediction may be elusive but there are definitely certain known factors that increase the risk for a person developing low back pain. Jobs that require a significant amount of driving in which the worker is subject to a significant amount of vehicular vibrations; jobs that require the worker to sit or stand for long periods of time or persons who are required to do heavy or frequent lifting are at risk.  

Seated workers increase the chance of developing low back pain by sitting for prolonged periods in an upright posture or leaning forward in their chairs. These postures concentrate increased pressures on the intervertebral discs. Since the health of the discs depends on a pattern of loading and unloading of body weight a failure to change position from time to time will also lead to the development of low back pain. 

What are the Causes of Low Back Pain? 

For the purposes of our discussion we are concerned with biomechanical causes of low back pain. In any assessment of low back pain non-mechanical conditions (ie. infectious processes, neoplasm, etc.) should be ruled out. Historically, sources of low back pain have been elusive at best and it is only in the past few years that we have understood the role of biochemical mediators in producing low back pain. Once we identify which spinal structures are pain-sensitive we must examine the normal mechanical dynamics involved between adjacent vertebrae and their supporting structures. 

We must first consider which structures of the spine are particularly pain-sensitive. These include the vertebral periosteum or outer layer of the bone; the spinal dura, which is the covering of the brain that extends over the entire spinal cord; the outer one third of the annulus fibrosus that makes up the intervertebral disc; the posterior longitudinal ligament which runs down the back of the vertebral bodies; and the associated vasculature. When the nerves that control these structures are irritated the result is pain.  

Two adjacent lumbar vertebra along with the disc that separates them make up the functional unit of the lumbar spine along with the two facet joints associated with each vertebrae. The articulating surfaces of the facets are covered with a synovial membrane that is also pain-sensitive.  

The facets are designed to accommodate flexion and extension and to some degree, rotation and lateral flexion of the torso while at the same time supporting it’s weight. The resulting mechanical forces associated with movement compress the joint surfaces and stress the related structures.  

In time the joints may undergo degenerative changes that can sometimes result in symptoms of pain in the area or the referral of pain to outlying areas. Nerve roots come off the spinal cord and exit through the intervertebral foramen which are openings formed between adjacent vertebra. 

With further industrialization and technological advancement in the workplace there continues to be an increasing incidence of work-related spinal injuries. Some of the causative mechanisms of lumbar failure in the workplace are the result of the compressive forces that are due to overloading the spinal muscles of the low back. There are also mechanical forces put on the lumbar facets, ligaments and lumbar discs from excessive lumbar flexion and rotation while lifting objects. Finally, there is increased risk of injury when the center of gravity of the load is a significant distance from the spine. 

How is Low Back Pain Prevented or Treated? 

Unfortunately, in general there has been a failure of the healthcare professions to reduce low back pain associated with spinal injuries in the workplace. Surgical procedures, once a common approach to the problem, in the last ten years have come to play a decreasing role, giving way to more conservative approaches. Even with the significant likelihood of developing the postoperative condition called failed back syndrome, characterized by disabling back pain, back problems continue to be the third most common reason for surgery. 

Passive modes of treatment such as prolonged bed rest and long-term medication have come to be realized as counter productive in preventing the acute low back pain patient from developing into a chronic disability. Returning the acute patient to normal function depends on an early aggressive strategy with a consideration of the psychosocial factors involved such as depression and despair that tend to perpetuate the condition.  

Active treatment options overlap with prevention and include life-style changes involving weight control and a full range of spinal rehabilitation exercises that enhance spinal flexibility and conditioning of the hip and spinal extensor muscles. Treatment should also include spinal manipulation and training in ergonomic work principals such as the correct lifting technique. While doing work tasks in the sitting posture ergonomic chairs should be used to evenly distribute the load of the torso on the lumbar discs. Seat rests and seat pans should support the natural curve of the lumbar spine and enhance forward pelvic rotation. Arms supports also serve to reduce pressure on the discs.

Sources:
1) Anderson, Gunnar B.J. “Epidemiology of Back Pain in Industry.” The Occupational Ergonomics Handbook. Ed. Waldemar Karwowski and William S. Marras. Bocca Raton: CRC press, LLC, 1999
2) Brier, Steven R. Primary Care Orthopedics. St. Louis: Mosby, Inc., 1999                                      
3) CUErgo (Cornell University Ergonomic Web), "ergo.human.cornell.edu/mbergo.schoolguide.html"                                                                        
4) Rose-Innes, MD, Andrew and John w. Engstrom, MD. “Low Back Pain: An Algorithmic Approach to Diagnosis and Management.” Geriatrics. WebMD.

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