Low Back Pain: 8 Questions Physicians Often Ask

ABSTRACT: The vast majority of episodes of low back pain have musculoskeletal causes and resolve on their own, although recurrence is common. Therapeutic exercise, aerobic fitness, and achieving an ideal body weight may help prevent recurrences. Consider imaging for patients who have recent significant trauma, unexplained weight loss, unexplained fever, immunosuppression, history of cancer, intravenous drug use, osteoporosis combined with prolonged use of glucocorticoids, age older than 70 years, focal neurologic deficit, progressive or disabling symptoms, or symptom duration of greater than 6 weeks. It is important to identify medical causes, lumbar radiculopathy, and spinal stenosis, since these diagnoses have potential neurological impact and have more specific treatments. Referral to a spine surgeon is indicated in cases of refractory radicular pain, cauda equina syndrome, spinal cord compression, or progressive neurological deficit; surgical referral may also be considered in the setting of persistent pain or neurological deficit after 6 weeks of non-operative management.

Low back pain is a widespread and costly complaint that affects most Americans at some point in their lives. In this article, we address 8 questions that physicians often ask about this common symptom.

When should I worry that back pain is caused by an ominous process, such as infection, tumor, or fracture?

1 It is important to always be concerned about this possibility; however, the overwhelming majority of cases of low back pain have musculoskeletal causes. Several guidelines exist that suggest when imaging is warranted. According to the American College of Radiology, one should consider imaging for a more concerning process when there is recent significant trauma, unexplained weight loss, unexplained fever, immunosuppression, history of cancer, intravenous drug use, osteoporosis combined with prolonged use of glucocorticoids, age older than 70 years, focal neurologic deficit, progressive or disabling symptoms, and duration of greater than 6 weeks.¹ Malignancy is less likely in patients with improving symptoms or absence of nocturnal symptoms, weight loss, or prior history of malignancy.

In patients with musculoskeletal low back pain, what can I tell them about why this happened and where this problem is headed?

2 Back discomfort is an exceedingly common symptom in the United States; it affects up to 84% of the population within their lifetime.² Genetic factors and aging are among the more important factors leading to degenerative disc disease, and psychosocial factors impact pain and disability.^3,4

Managing expectations is an important responsibility of the treating clinician. In the midst of agonizing or even catastrophic discomfort, patients frequently seek reassurance and consolation, in order to obtain some normalcy in their lives.

After red flags for worrisome pathology are excluded, the most important next step is to reassure the patient that the symptoms are a “safe pain” and probably not dangerous. Tell the patient that although symptoms of the acute low back pain flare can be extreme, it is exceedingly common and usually improves on its own. In general, 10% to 28% of patients will continue to have residual pain, and approximately 10% will experience pain that results in disability.^5-7 Both the clinician and the patient should recognize that recurrences are common, and prevention and management of the recurrences will require optimal management of general health principles discussed below.

The above conversation typically and naturally generates the further inquiry: “Will it get worse?” It is important for the patient to recognize that while the radiographic and MRI appearance of the degenerative changes will worsen, often the symptoms of pain and functional disability do not worsen. Only a minority of patients seek further medical care after acute flares.⁸ Most people are able to remain functionally active and fully participatory in their lives, albeit with some chronic symptoms.

Unfortunately, recurrences of low back pain are common. They can affect up to 64% to 77% of patients each year.⁹ However, it is important to emphasize to your patients that similar to the initial episode, most recurrences have a favorable prognosis.

Patients commonly ask what caused the current symptoms. Because of the lack of specificity of physical examination and MRI findings, many patients who present to primary care in the initial flare have low back pain that cannot reliably be attributed to a specific disease or spinal abnormality. It is important to identify patients with medical causes, lumbar radiculopathy, and spinal stenosis, since these diagnoses have potential neurological impact and have more specific treatments. Patients with nonspecific low back pain have numerous potential musculoskeletal causes that only need further anatomic delineation when spinal injection therapy or surgery is considered.

There is little compelling evidence that back braces, ergonomic chairs, or chiropractic manipulation prevent recurrences of back pain, but they can be useful tools to help manage daily pain and disability and are in most cases safe.^10,11 There is some evidence that therapeutic exercise, aerobic fitness, and achieving ideal body weight may be the more promising preventive alternative.¹²

What differential diagnoses should I consider?

3 The most common cause of low back pain is mechanical due to nonspecific degenerative causes (85%).¹³ This broad descriptive diagnosis encompasses entities such as lumbar sprain/strains, lumbar facet syndrome, lumbar discogenic pain, and sacroiliac joint dysfunction.

Herniated discs that cause lumbar radiculopathy occur in only 3% to 5% of the population.¹⁴ This may present as radiculopathy or nerve root irritation that produces radiating sharp discomfort down the lower extremity. In extremely rare instances, very large disc herniations, infections, or tumors may invade the spinal canal resulting in cauda equina syndrome, which presents as incontinence of bowel, urinary retention, saddle anesthesia, and leg weakness.¹³ This is a surgical emergency and requires immediate referral to a spine surgeon. Spinal stenosis is another cause of mechanical low back pain and is usually a result of bony hypertrophic facets, thickened ligamentum flavum, disc bulging, and spondylolisthesis.¹³

The full differential of low back pain is exceedingly broad but must be considered in order to avoid missing dangerous disorders. Non-mechanical causes include visceral disorders and disease of pelvic organs (including prostatitis, renal disease, aortic aneurysm, pancreatic disease, gall bladder disease, endometriosis, and more), neoplasms and tumors, lymphomas and leukemias, multiple myeloma, infectious processes (septic discs, epidural abscess, paraspinous abscess, osteomyelitis, shingles), and rheumatologic disorders (inflammatory bowel disease, ankylosing spondylitis, psoriatic spondylitis, HLA-B27 inflammatory arthritis). Hip disorders are also well known for referring pain to the low back. One should also be aware of vascular disorders such as aortoiliac disease that can produce vascular claudication that may be confused with the pseudoclaudication associated with lumbar stenosis. One should also consider diabetic plexopathy, gluteal muscle injuries, and trochanteric bursitis in the differential diagnosis.¹³

Physical examination signs often can suggest spinal nerve root irritation from a disc herniation with resultant tethering against the disc and dura. For lumbar herniated nucleus pulposus, the straight leg raise test is useful to confirm lumbar radiculopathy involving the L5 or S1 spinal nerve roots. This test is often performed with the patient supine. The examiner passively raises the affected leg, looking for a reproduction of symptoms distal to the knee between 30 and 70 degrees of elevation.

The crossed straight leg raise test can also be performed. The examiner raises the unaffected leg to between 10 and 60 degrees of elevation. If symptoms in the affected leg are provoked by elevation of the unaffected leg, it is considered positive. The positive straight leg test is sensitive (91%) but nonspecific (26% specific), while the crossed straight leg test is less sensitive (29%) but highly specific (86% to 90%.)¹⁵

One should also focus on neurological testing of the L4, L5, and S1 nerve roots, given that the majority of lumbar disc herniations involve these nerve roots.^13,15 The L5 nerve root may be tested with strength of the ankle and great toe dorsiflexion and sensory dermatome of the great toe.¹³ The S1 nerve root may be tested by single leg toe raise, sensation of the lateral foot, and ankle reflexes. In addition, the L4 nerve root can be evaluated by knee strength and patellar reflexes. The femoral stretch test is done to screen for upper lumbar radiculopathy (L2, L3, L4) and is performed with the patient prone; the knee of the affected limb is flexed, and reproduction of familiar thigh pain is considered positive.

Lumbar stenosis typically affects patients over 60 and is characterized by discomfort in the buttock, thigh, or leg with standing or walking. Symptoms often improve when the patient leans on a cart or walks uphill or at a faster pace. Symptoms often worsen when the patient walks downhill, walks slowly, or stands for a prolonged period. Patients typically have some lower extremity vibratory sensory loss, a negative straight leg raise, and usually symmetric strength.

What are indications for obtaining imaging for patients with back pain, and what should I order?

4 Order a test when it affects management. Even plain radiographs, although inexpensive, expose the patient to radiation and demonstrate abnormalities that may cause unnecessary patient concern. Plain films are useful for identifying fractures, spondylolisthesis, and scoliosis, and for observing alignment in patients with persistent or concerning clinical features.

CT and MRI are helpful for evaluating patients for malignancy and infection, and for identifying degenerative structures. Unfortunately, these imaging studies frequently detect asymptomatic abnormalities. According to the American Pain Society guidelines, CT or MRI should be ordered for patients with severe or progressive neurological symptoms or suspicion of a serious underlying condition.¹⁵

I prefer to obtain an MRI scan as the imaging study of choice because it is useful for the diagnosis of infection, malignancy, disc herniation, and spinal stenosis, and for the assessment of the acuity of a fracture. CT is useful for visualizing bony structures in the setting of trauma, and when MRI is precluded because of factors such as the presence of a pacemaker, implanted defibrillator or other implantable device, or certain cerebrovascular stents. Most metal devices placed during orthopedic procedures do not preclude MRI. For cases of chronic low back pain with or without radicular symptoms, we recommend obtaining diagnostic imaging after initial efforts at non-invasive conservative care.

What is the role of exercise and activity modifications in patients with back pain?

5 The simple answer is—it depends. Timing of presentation is critical in the exercise prescription. For acute low back pain, systematic reviews report that there is limited evidence that exercise is beneficial.^16,17 However for subacute and chronic low back pain, exercise therapy has been shown to have demonstrable benefits. Furthermore, the improvements may last up to 1 to 3 years.¹⁸

There is an emerging school of thought that the maintenance of lumbar spinal stability over time can limit the pain associated with degenerative disc disease and spondylosis. Specifically, the multifidi and transversus abdominis are two muscle groups associated with lumbar stability.¹⁹ The multifidi are rich in muscle spindles and therefore useful in stabilizing individual spinal segments, providing proprioceptive feedback of movement. There is evidence that these muscles may be atrophied in patients with low back pain,²⁰ and some studies have suggested that their activation may be delayed in patients with back pain.

Therefore, some exercise regimens focus on core strengthening targeting transversus abdominis activation and strengthening.^19,21 It is important to include aerobic activity, range of motion, stretching, cognitive behavioral strategies, and strengthening. After patients work with a physical therapist, encourage them to be lifelong exercisers and try to have them continue home exercise in a capacity that is interesting enough to be enjoyable to them. We are not dogmatic in the specifics, but rather provide anticipatory guidance as to what may provoke symptoms given their spinal mechanics. A systematic review of 43 trials found exercise to be effective for pain relief and functional outcomes.²²

What is the role of injection therapy in low back pain and radiculopathy?

6 Spinal injections with corticosteroids have been used in patients with radiculopathy, spinal stenosis, and nonspecific low back pain. An interlaminar, transforaminal, or caudal approach may be used. We usually consider such interventions in patients with persistent (of 6 or more weeks’ duration) radicular symptoms despite NSAIDs, opiates, and physical therapy. In patients with very severe symptoms that do not respond to these measures, or that cause insomnia, work disability, or mood impact despite these measures, we will consider injection therapy sooner.

Facet injections and medial branch blocks are used to treat chronic low back pain. Facet injections are designed to inject corticosteroid and lidocaine in the area of arthropathy, whereas medial branch blocks inject lidocaine to numb the medial branch of the dorsal ramus of the spinal nerve that innervates the facet joint. Two successful medial branch blocks may lead the clinician to consider performing radiofrequency ablation of the involved nerves.

When is surgery helpful for lumbar spine disorders?

7 Referral to a spine surgeon (neurosurgery or orthopedics) is indicated in cases of refractory radicular pain, cauda equina syndrome, spinal cord compression, or progressive neurological deficit. Spinal cord compression may be the result of severe stenosis, cancer, fracture, or other pathologies. Surgical referral may also be considered in the setting of persistent pain or neurological deficit after 6 weeks of non-operative management. The results of the Spine Patient Outcomes Research Trial (SPORT) trial support the use of surgery for patients with more than 3 months of radicular pain due to a herniated disc, spinal stenosis with pseudoclaudication, and spondylolisthesis.^23-25

In more than 90% of those patients who have herniated disk syndromes, symptoms diminish over the course of several months without surgery.²⁶ Surgical decisions should be made with the favorable natural history in mind. Surgery usually has an excellent outcome for patients with limb pain; however, low back pain generally is not benefitted in the long run.

Discectomy has complications, although they are uncommon. Operative mortality is approximately 0.15%. Discectomy is associated with nerve injury in about 1% of patients, deep venous thrombosis in 1% to 2%, and pulmonary embolism in less than 1%. Wound infections occur in about 1% to 2% of patients. About 10% require repeated operations, a high rate compared with other surgeries, hence the expression “failed back surgery syndrome.”

Although surgery relieves symptoms more effectively than does non-operative therapy, 2 years after treatment (whether operative or non-operative) all patients have the same level of symptoms. This finding suggests gradual resolution of disk-related symptoms among patients who did not have surgery and recurrence among those who did.

The natural history of spinal stenosis is less favorable: only about 20% of patients experience substantial improvement over time.²⁷ This would provide less rationale for temporizing. On the other hand, patients with spinal stenosis are older and more often have co-morbid conditions that increase the likelihood of complications. Surgical outcomes are more favorable when leg pain, rather than back pain, is predominant and less favorable when the patient has worse functional status and a greater number of co-morbid conditions.^28,29

Observational studies suggest that surgery for spinal stenosis is successful in about 65% to 75% of patients.³⁰ The rate of reoperation ranges from 10% to more than 20% in various series. Laminectomy should be considered carefully for patients who find their symptoms unacceptable and have functional limitation.

How do I help patients make the best decision regarding surgery for low back pain?

8 Our goal is to help patients make decisions that are fully informed and consonant with their preferences. By “fully informed,” we mean that patients understand the risks and benefits of the choices they face. By “consonant with preferences,” we mean that patients’ decisions are consistent with their values. For example, patients who are more averse to taking risks will tend to opt for less risky treatments. Those who place great emphasis on functioning at a high level may be willing to consider a riskier treatment that can improve function.

Decision-making tools have been developed to make this process easier. In one randomized controlled trial, patients considering disk surgery who received the decision-aid intervention were less likely to opt for surgery than those who received a control intervention. In contrast, among patients considering surgery for spinal stenosis, those who received the decision aid were somewhat more likely to opt for surgery.³¹ These findings suggest that informed, preference-consonant decisions may differ substantively from usual clinical decisions.