Most Americans will have at least one episode of low back pain at some point during their lifetime, according to the American Academy of Orthopaedic Surgeons (AAOS). Approximately half of them will have a recurrence within a year. The good news is that 90% of patients who experience low back pain will recover completely within about six weeks without surgery. For those who do not recover so quickly, low back pain can be a prolonged, agonizing, and costly experience.

The underlying causes of low back pain are not always obvious and can be complex. The vast majority of acute low back pain cases result from injury such as sprain or strain, while the causes of chronic low back pain are usually multifactorial. Pain may emanate from any of a number of sources in the spine. These include irritated large nerve roots that go to the legs and arms; irritated smaller nerves that innervate the spine; strained large paired lower back muscles (erector spinae); damaged bones, ligaments, or joints; and damaged intervertebral discs.1 What’s more, many types of low back pain have no known anatomical cause, or, in other cases, the pain generator may not be identifiable, according to the AAOS. Each of those situations can be particularly frustrating for practitioners.

“The structures that cause pain have overlapping areas that are either hard to localize or are too deep to palpate,” said Gerard Malanga, MD, a clinical professor of physical medicine and rehabilitation at the University of Medicine & Dentistry of New Jersey in Newark. He also is director of the pain center at Overlook Hospital in Summit, NJ.

While it is not always possible to pinpoint the origin of pain to one specific site, it is usually possible to identify the type of low back pain involved. Once that is accomplished, the appropriate rehabilitation processes can be determined, according to Malanga.

Classifying low back pain

Low back pain is typically classified as either acute or chronic.1 Acute pain generally lasts from a few days to a few weeks. In an acute episode, low back pain can often be very severe for a few days and then will improve. The length of time between episodes varies greatly from person to person, as do both the length and intensity of each episode and the ability of each individual to cope with the pain. By two to four weeks, most patients feel significant improvement, according to the AAOS.

Chronic low back pain is generally defined as pain that persists for more than three months. The pain may be progressive, or it may occasionally flare up and then return to a lower or less severe level in which the patient is able to continue with his or her normal activities of daily living.

When determining the underlying cause of low back pain, both the type of pain (a description of how the pain feels) and the area of pain distribution (where it is felt) can help guide the practitioner in making a diagnosis and determining the appropriate treatment plan.1 Lower back pain can be further classified based on the area of pain distribution: axial pain, also called simple or mechanical low back pain; referred pain; or radicular pain, also called sciatica.

Axial pain represents the most common type of low back pain, and it is usually nonspecific in that the symptoms are frequently self-limited and often resolve on their own. This type of low back pain can vary widely. The pain can be sharp or dull, can be felt constantly or intermittently, and can range from mild to severe. The most common type of axial back pain is mechanical and is characterized as pain that gets worse with certain activities or sports or with certain positions (e.g., sitting for long periods).

Referred low back pain is not as common as the other two types. It is usually felt in the low back area and tends to radiate into the groin, buttocks, and upper thigh. The pain often moves around and rarely radiates below the knee. Referred low back pain tends to be achy, dull, and migratory and tends to come and go. It also often varies in intensity. It can result from the identical injury or problem that causes simple axial back pain and is often no more serious than axial back pain.

Radicular pain is often felt deeply and persistently and can usually be reproduced with certain activities and positions such as sitting or walking. It can be accompanied by numbness and tingling, muscle weakness, and loss of specific reflexes. Radicular pain may be related to aging of the disk. As a result of wear and tear on the spine, ligaments, and disks, a disk may begin to protrude or collapse and, as a result, may exert pressure on the nerve root leading to a leg or foot. The pain that results is called sciatica.

Sciatica is one of the most common forms of pain caused by compression of a spinal nerve in the low back. It may result from compression of the lower spinal nerve roots (L5 and S2). Sciatica is a set of symptoms that describe where the pain is felt, but it is not considered an actual diagnosis.1 The clinical diagnosis is usually arrived at through a combination of the patient’s history (including a description of the pain) and a physical exam. Imaging studies (magnetic resonance imaging, computed tomography [CT]-myelogram) are used to confirm the diagnosis and will usually show impingement on the nerve root.

“It’s typically more difficult to understand what causes axial low back pain than it is to understand what causes sciatic pain,” said Christopher Standaert, MD, a clinical associate professor of rehabilitation medicine at the University of Washington in Seattle. “With sciatic pain or neurological symptoms, we can look for known pain referral patterns and well-established patterns of neurological findings associated with a given nerve root.”

While there are many causes of low back pain, most cases can typically be linked to either a general cause, such as muscle strain, or a specific and diagnosable condition, such as degenerative disk disease or a lumbar herniated disk.1 The type and location of pain are key elements in making a preliminary diagnosis and determining an appropriate treatment plan.

Diagnosing the pain

Making an accurate diagnosis of the cause of low back pain is often a challenge and involves a combination of obtaining a thorough patient history along with conducting a physical exam and diagnostic tests.1 The history and physical exam help determine if a patient’s pain is more likely to be caused by a soft tissue (muscle, ligament, or tendon) problem that will likely heal itself, or by a more serious underlying medical condition such as a fracture, infection, or tumor.1

When conducting a physical exam, a practitioner should check for evidence of nerve problems by evaluating strength, sensation, and reflexes, according to the AAOS. To guide clinicians in this process, the American College of Physicians and the American Pain Society have published four recommendations for the evaluation of low back pain (table).3

Standaert believes that in addition to the physical exam, a thorough neurological exam of the lower extremities is important for anyone with low back complaints.

“I look for local tenderness and restrictions of motion, including in the hips and pelvis,” Standaert said. “I also observe gait closely and assess the lower extremities, including the feet, ankles, knees, and hips, for biomechanical issues that may be contributing to low back pain.”

When Malanga conducts a physical exam for a patient with low back pain, he looks for three key indicators. He begins by examining the gluteus muscles, which are important for maintaining a level pelvis when walking and running.

“I have my patients stand on one leg to see if their pelvis drops at all,” he said. “If so, it indicates that they have weakness of their gluteus muscles.” For such patients, he recommends a rehab process that strengthens those muscles, including the hip abductors and extensors.

Malanga then examines how the patient’s spine moves. About 90% of all disk-related low back pain is related to L5 and S2 levels, according to Malanga. He uses the McKenzie method (see “McKenzie method categorizes patients by their mechanical responses to pain,” page 24).

During assessment, patients are observed to see which movements make the pain better or worse. The approach is based on the idea that extending the spine can provide significant pain relief to patients.4

Malanga has the patient bend forward and backward repeatedly, which enables him to look at segmental motion. He compares side-to-side differences in motion and looks at individual segments of the upper, middle, and lower spine.

“It’s important not to just focus on the entire lumbar spine as a whole, but to look at each of the individual segments,” he said. “Look for segments that tend to move more versus some that don’t move at all.”

Malanga then observes pelvic positioning and measures actual leg length to compare it to perceived leg length discrepancies, which are usually related to muscle tightness and imbalances in strength. These imbalances are often associated with a restriction in motion that can result in low back pain.

“Muscle tightness about the pelvis can rotate the pelvis forward or backward, which makes the leg length appear higher or lower (shorter or longer), when actually the leg length is normal,” he said. “The remedy is to recognize these muscular imbalances, then stretch the hip flexors and other muscles around the pelvis, depending on which ones appear to be tight.”

Limits of imaging

Radiography and other imaging techniques, including MRI and CT, are not used routinely in determining the cause of acute low back pain, according to the AAOS. These techniques are more likely to be helpful when the pain does not improve on its own after a few weeks or when more severe problems are evident.

“I use imaging if I need to look for something in particular,” Standaert said. “If I see ‘red flags’ in a patient’s history or during a physical examination that suggest fracture, tumor, infection, or significant neurological injury, then I need to urgently image the patient.”

Although an MRI scan, similar to x-rays, can sometimes help a practitioner determine the source of a back problem, it also often shows nonspecific findings, which may or may not be related to the patient’s low back pain, according to the AAOS. Patients who are middle-aged and older often show evidence of these findings, which include disk space narrowing, spurring, spina bifida occulta (incomplete formation of the lamina and spinous process), mild scoliosis, and a decrease in lumbar lordosis (the normal curvature of the spine when viewed from the side).2

“A 40-year-old patient will most likely show some evidence of degenerative disk disease or herniations, which, although present, might not be causing or related to the low back pain,” Malanga said.

MRI is often the next test ordered after an x-ray if necessary.2 It can reveal the level of disk degeneration and whether any material has migrated outside the normal disk confines. These scans must be interpreted with caution, according to Standaert.

“Normal changes associated with aging make it difficult to tell whether the findings are responsible for the low back pain,” he said.

Additional diagnostic tests may be required to determine the cause of low back pain.2 These may include CT scans; bone scans to detect areas of possible infection, tumor, or fracture; electromyography and nerve conduction velocity tests to see how well the nerves in the arms and legs conduct electrical signals; and bone density studies if osteoporosis is suspected.2

Standaert and Malanga share the opinion that MRIs and x-rays are not necessary in all cases, and that practitioners often overutilize these techniques.

“In general, if you obtain a detailed history and you do a good exam, you often don’t need to use imaging techniques,” they said.

This is part one of a two-part article. The second part will explore therapeutic options, rehabilitation exercises, and prevention strategies for low back pain.

References

1. Yishay AB. Understanding low back pain (lumbago). www.spinehealth. com, accessed 12/11/08.

2. American Academy of Orthopaedic Surgeons. Low back pain. http://orthoinfo.aaos.org, accessed 12/15/08.

3. Chou R, Qaseem A, Snow V, et al. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med 2007; 147(7):478-491.

4. The McKenzie Institute. The McKenzie method. www.mckenziemdt. org, accessed 12/15/08.