Fisioterapeuta Luís Miguel Brazão Gouveia: WORK-RELATED BACK PAIN

Back pain, like tooth decay and the common cold, is an affliction that affects a substantial proportion, if not the entire population, at some point in their lives. Nobody is immune to this condition nor its potential disability which does not discriminate by gender, age, race or culture. It has become one of the leading causes of disability in our society and the cost of treatment has been increasing progressively each year, without any obvious effect on the frequency and severity of the condition. The search for a cure and the elimination of back pain does not appear to be a viable option at this point in our understanding of back pain. A reasonable goal, however, is to improve the ability of clinicians to determine the cause of back pain in a substantial proportion of patients, to identify conditions likely to lead to serious disability if not treated promptly, to reduce the symptoms of back pain, to increase functional capacity and to reduce the likelihood of recurrences.

EPIDEMIOLOGY

The prevalence of back pain in the adult population varies with age. There are a number of surveys in multiple countries that reveal a point-prevalence of 17–30%, a 1-month prevalence of 19–43% and a lifetime prevalence of 60–80%. The likelihood that an individual will recall on survey that they have experienced back pain in their lifetime reaches 80% by the age of 60 years, and there is some evidence that the remaining 20% have simply forgotten prior episodes of back pain or considered such episodes as a natural part of life and not worth reporting. At the age of 40 years, the prevalence is slightly higher in women, while, after the age of 50, it is slightly higher in men. The majority of these episodes of back pain are mild and short-lived and have very little impact on daily life. Recurrences are common and one survey found that up to 14% of the adult population had an episode of back pain each year that lasted 30 days or longer and at some point interfered with sleep, routine activities or work. Approximately 1% of the population is permanently disabled by back pain at any given point, with another 1–2% temporarily disabled from their normal occupation.

Children and adolescents are not immune from back pain. Surveys reveal that approximately 5% of all children have a history of back pain that interferes with activity, with 27% reporting back pain at some time.Normal spinal anatomy and physiology The spine is one of the most complex structures in the body. It is a structure that includes bones, muscles, ligaments, nerves and blood vessels as well as diarthrodial joints. In addition, the structures that make up the spine include the intervertebral discs, the nerve roots and dorsal root ganglia, the spinal cord and the dura mater with its spaces filled with cerebrospinal fluid. Each of these structures has unique responses to trauma, aging and activity.

WORK-RELATED BACK PAIN

Back injuries make up one-third of all work-related injuries or almost one million claims in the United States each year. Approximately 150 million workdays are lost each year, affecting 17% of all American workers. Half of the lost workdays are taken by 15% of this population, usually with prolonged periods of time loss, while the other 50% of lost work days are for periods of less than 1 week. The incidence rates for work-related back injuries vary, depending on the type of work performed. The factors that increase the likelihood of back injury are repetitive heavy lifting, prolonged bending and twisting, repetitive heavy pushing and pulling activities and long periods of vibration exposure. Work that requires minimal physically strenuous activity, such as the finance, insurance and service industries, has the lowest back injury rates, whereas work requiring repetitive and strenuous activity such as construction, mining and forestry has the highest injury rates.

PATHOLOGY AND BACK PAIN

There is a strong inclination on the part of clinicians and patients suffering from back pain, especially if it is associated with disability, to relate the symptoms of pain to pathological changes in spinal tissues. For this reason, there is a tendency to look for anatomical abnormalities to explain the presence of pain, by ordering X-rays, computerized tomography (CT) or magnetic resonance imaging (MRI) studies. It is tempting to point to changes in anatomical structure seen on these studies as the cause of the symptoms. Unfortunately, the assumption that the lesion seen on these studies is the cause of the pain is not always valid. Degenerative changes occur in virtually all patients as part of the normal aging process. At age 20, degenerative changes are noted on X-ray and MRI in less than 10% of the population. By age 40, such changes are seen in 50% of the asymptomatic population and, by age 60, this number reaches over 90%. Disc and joint pathology is noted in 100% of autopsies of persons over the age of 50. These changes can affect multiple levels of the spine and can be severe in the absence of symptoms. Pathology in the intervertebral disc can also exist in the absence of symptoms. Disc protrusion or herniation can be found in 30–50% of the population in the absence of symptoms. Even large and dramatic disc herniations and extrusions can be found in asymptomatic individuals. Changes in the intervertebral disc seen on discography, including fissures and radial tears, have recently been found to exist in patients without back pain. It is, therefore, not possible to interpret pathology seen on imaging studies as the origin of a person’s back pain without looking for other contributing factors or clinical findings.

PHYSIOLOGY OF BACK PAIN

There are a number of factors that have been implicated in the genesis of back pain and disability that can be used to determine whether a pathological process seen on imaging studies is associated with symptoms experienced by a patient. Certain of these factors are based on epidemiological studies, while others are based on clinical findings and physiological tests. Pain in any structure requires the release of inflammatory agents that stimulate pain receptors and generate a nociceptive response in the tissue. The spine is unique in that it has multiple structures that are innervated by pain fibers. Inflammation of the posterior joints of the spine, the intervertebral disc, the ligaments and muscles, meninges and nerve roots have all been associated with back pain. These tissues respond to injury by releasing a number of chemical agents that include bradykinin, prostaglandins and leukotrienes. These chemical agents activate nerve endings and generate nerve impulses that travel to the spinal cord. The nociceptive nerves, in turn, release neuropeptides, the most prominent of which is substance P. These neuropeptides act on blood vessels, causing extravasation, and stimulate mast cells to release histamine and dilate blood vessels. The mast cells also release leukotrienes and other inflammatory chemicals that attract polymorphonuclear leukocytes and monocytes.

These processes result in the classic findings of inflammation with tissue swelling, vascular congestion and further stimulation of painful nerve endings. The pain impulses generated from injured and inflamed spinal tissues are transmitted via nerve fibers that travel through the anterior (from nerves innervating the extremities) and posterior (from the dorsal musculature) primary divisions of the spinal nerves and through the posterior nerve roots and the dorsal root ganglia to the spinal cord, where they make connections with ascending fibers that transmit the pain sensation to the brain. The spinal cord and brain have developed a mechanism of modifying the pain impulses coming from spinal tissues. At the level of the spinal cord , the pain impulses converge on neurons that also receive input from other sensory receptors. This results in changes in the degree of pain sensation that is transmitted to the brain through a process commonly referred to as the ‘gate control’ system. The pain impulses are modified further through a complex process that occurs at multiple levels of the central nervous system. The brain releases chemical agents in response to pain known as endorphins. These function as natural analgesics. The brain can also block or enhance the pain response by means of descending serotonergic modulating pathways that impact with pain sensations both centrally and at the spinal cord level. The latter mechanism is felt to be responsible for the strong impact of psychosocial factors on the response to pain and the disability associated with back pain.

The pain centers in the spinal cord and brain can also change through a process known as plasticity which may explain the observation that many patients develop chronic pain that is more widespread than the pathological lesion and continues after the resolution of the peripheral inflammatory process.

APPROACHING THE PATIENT WITH BACK PAIN

The factors that determine the degree of back pain, and especially the amount of disability associated with the pain, are therefore the result of multiple factors. Structural pathology sets the stage and is the origin of the painful stimulus. The natural healing process, in most situations, results in the resolution of back pain within relatively short periods. Physical stress placed on the back through work and leisure activities may slow the healing process or irritate spinal pathology such as degenerative changes or disc protrusion. It is, however, the psychosocial situation of the patient that determines the level of discomfort and the response of a patient to the painful stimulus.

The patient’s psychological state, level of satisfaction with work and personal life as well as his/her social and spiritual life may impact upon the central modulation system in the brain and modify the response to pain. In this volume, a great deal of emphasis is placed on visualization of spinal lesions that can result in spinal pain. To rely on anatomical changes to determine the cause of back pain can, however, be very misleading to the clinician through the mechanisms described above. There are other examples in science that can be used as a model for looking at spinal pain. The Danish pioneer of quantum physics, Niels Bohr, claimed that science does not adequately explain the way the world is but rather only the way we, as observers, interact with this world. Early in the last century, it was discovered that light could be explained in terms of either waves or particles, depending on the type of experiment that was set up by the observer. Bohr postulated that it was the interaction between the scientist, as the observer, and the phenomenon being studied, in this case light, that was important. The same thing can be said forthe clinician approaching a patient with back pain.The conclusions reached by the clinician regarding the etiology of back pain in a specific case are often dependent on the interaction between the patient and the clinician and the training and experience brought to the decision-making process by both individuals.

There are other ways of looking at back pain. Chaos theory postulates that there is a delicate balance between disorder and order. The origin of the universe is generally explained by the ‘Big Bang’ theory which states that, in the beginning, there was total disorder which was followed by the gradual imposition of order through the creation of galaxies, stars and planets. This process is perceived as occurringthrough a delicate balance between the forces of gravity and the effects of the initial explosion. This process emphasizes that small changes at the beginning of a process or reaction can result in large changes over time. If one applies this analogy to the interaction between patients with back pain and their physicians, the outcome of treatment can be perceived as being impacted upon by a number of beneficial influences or ‘little nudges’ and harmful attitudes or ‘little ripples’ (Table 1). The patient’s symptoms can be positively impacted through such processes as listening, caring, laughter, explanation, encouragement, attention to detail and even prayer and negatively impacted by fear, anxiety, anger, uncertainty, boredom and haste. The manner in which a physician uses these nudges and helps the patient avoid the ripples can have a large effect on the impact of back pain on the patient’s life. The most accurate diagnosis possible is dependent on accurately observing and listening to the patient, the physical examination and the results of all testing in combination with the intuition that is gained from experience from treating multiple similar patients.

The fine balance between different factors impacting on back pain can be illustrated by a few simple examples.

Example 1

A 50-year-old woman presented to her doctor with symptoms and signs of a disc herniation confirmed by CT scan. She was the owner of a small cattle range and was worried about the condition of her animals. She underwent surgery to correct the disc herniation but her convalescence was prolonged for no apparent reason. After several months, the condition of her cattle herd improved and, at the same time, the patient’s symptoms improved. This raises the question as to the link between the patient’s symptoms, the disc herniation and the condition of her cattle.

Example 2

A 45-year-old gentleman in a position with a responsible insurance company presented to his doctor with symptoms and signs of severe L4–5 instability confirmed by stress X-rays. The patient underwent a posterolateral fusion. At 3 months, the fusion was solid but the patient’s symptoms did not improve. Further questioning revealed that he felt stressed and was unhappy in his work. At 6 months, he became symptom-free without further treatment. The only evident change in his status was the resolution of his difficulties at work.

Example 3

A 35-year-old gentleman with a wife and two small children was admitted to the hospital on an emergency basis with suspected cauda equina syndrome. A psychotherapist assigned to the case discovered that the patient found the presence of his mother-inlaw intolerable. Arrangements were made for the mother-in-law to live elsewhere and the patient made an uneventful recovery without the necessity of surgery.

Table 1 Beneficial influences (nudges) and harmful influences (ripples) which impact on the outcome of treament for back pain

Harmful influences                        Beneficial influences

Fear                                            Listening and caring
Anxiety                                       Laughter
Anger                                         Explanation
Uncertainty                                 Encouragement
Boredom                                    Attention
Haste                                         Prayer

THE BONY VERTEBRAE

Each of the bony elements of the back consist of a heavy kidney-shaped bony structure known as the vertebral body, a horseshoe-shaped vertebral arch made up of a lamina, pedicles and seven protruding processes. The pedicle attaches to the superior half of the vertebral body and extends backwards to the articular pillar. The articular pillar extends rostrally and caudally to form the superior and inferior facet joints. The transverse processes extend laterally from the posterior aspect of the articular pillar where it connects to a flat broad bony lamina. The laminae extend posteriorly from the left and right articular pillars and join to form the spinous process. Two adjacent vertebrae connect with each other by means of the facet joints on either side. This leaves a space between the bodies of the vertebrae which is filled with the intervertebral disc. The intervertebral foramen for the exiting nerve root is formed by the space between the adjacent pedicles, facet joints and the vertebral body and disc. The integrity of the nerve root canal is therefore dependent on the integrity of the facet joints, the articular pillars, the vertebral body endplates and the intervertebral disc. The bony vertebrae can be visualized on standard radiographs and on CT scan using X-radiation. The bones can also be visualized on MRI, although with not quite the same definition. The metabolism of the bony vertebra can be visualized by means of a technetium bone scan.

Figure 1.1 Superior view of an isolated lumbar vertebra

This view demonstrates the two posterior facets and the vertebral body endplate where the disc attaches. The facets and the disc make up the ‘three-joint complex’ of the spinal motion segment. The body of the vertebra is connected to the articular pillars by the pedicles. The superior and inferior articular facets extend from the articular pillars to connect with the corresponding facets of the vertebrae above and below, to make up the posterior facets. The lateral transverse processes and the posterior spinous process form the attachments for paraspinal ligaments and muscles.

THE INTERVERTEBRAL DISC
The intervertebral disc is made up of an outer annulus fibrosis and a central nucleus pulposus. It is attached to the vertebral bodies above and below the disc by the superior and inferior endplates. The nucleus pulposus a gel-like substance made up of a meshwork of collagen fibrils suspended in a mucopolysaccharide base. It has a high water content in young individuals, which gradually diminishes with degenerative changes and wit the natural aging process. The annulus fibrosis is made up of a series of concentric fibrocartilaginous lamellae which run at an oblique angle of about 30º orientation to the plane of the disc. The fibers of adjacent lamella have similar arrangements, but run in opposite directions. The fibers of the outer annulus lamella attach to the vertebral body and mingle with the periosteal fibers. The fibrocartilaginous endplates are made up of hyaline cartilage and attach to the subchondral bone plate of the vertebral bodies. There are multiple small vascular perforations in the endplate,which allow nutrition to pass to the disc.
The intervertebral disc is not seen on standard Xray, but can be visualized by means of MRI scan and

CT scan. The integrity of the inner aspects of the disc is best visualized by injecting a radio-opaque agent into the disc. This material disperses within the nucleus and can be visualized radiologically as a discogram.

THE POSTERIOR FACETS

The facet joints connect the superior facet of a vertebra to the inferior facet of the adjacent vertebra on each side and are typical synovial joints. The articular surfaces are made of hyaline cartilage which is thicker in the center of the facet and thinner at the edges. A circumferential fibrous capsule, which is continuous with the ligamentum flavum ventrally, joins the two facet surfaces. Fibroadipose vascular tissue extends into the joint space from the capsule, particularly at the proximal and distal poles. This tissue has been referred to as a meniscoid which can become entrapped between the facets.
The posterior facets can be seen on X-ray but only to a limited extent. Degenerative changes and hypertrophy of the facets can be visualized to a greater extent on CT and MRI. Radio-opaque dye can also be injected into the joint and the distribution of the dye measured.

Figure 1.2 Lateral view of the L3 and L4 vertebrae

This projection demonstrates the manner in which the facets join. The space between the vertebral bodies is the location of the cartilaginous intervertebral disc. Courtesy Churchill-Livingstone (Saunders) Press