Low Back Pain
Pain Management Secrets, Chapter 20, 119-127
1
What are the most common causes of acute back pain?
In most cases of acute back pain, no clear pathophysiologic mechanism is defined, and patients are diagnosed as having “back strain.” Episodes are usually preceded by minor trauma, heavy lifting, or a “near fall.” Direct trauma is rarely a cause. A small minority of patients have acute medical illnesses that cause back pain.
The first urgent crossroad in the diagnosis of low back pain is to decide whether the patient has a medically emergent condition (tumor, infection, or trauma) or not. The signs and symptoms that should alert the clinician to impending disaster are focal spine tenderness, fever, weight loss, or bowel or bladder dysfunction. More than 90% of cases of so-called benign acute low back pain resolve spontaneously.
2
Why does the back hurt?
Erect posture forces the spine into a position in which it is constantly exposed to minor trauma and to stress on pain-sensitive structures. These pain-sensitive structures are the supporting bones, articulations, meninges, nerves, muscles, and aponeuroses. The vertebral body, despite being short, is actually a long bone with endplates of hard bone and a center of cancellous bone. It is innervated by the dorsal roots. In general, the periosteum, including the periosteum associated with the spine, is markedly pain-sensitive. (This is why, for example, banging the shin is so painful: the periosteum is unprotected.) The articulations (facet joints) are true diarthrodial joints and have a capsule and meniscus. The capsule and bones are richly innervated with nociceptors and are subjected to stress every time the spine turns or bends.
3
Why do some patients with absolutely no evidence of spine injury complain of chronic, disabling back pain?
The answer here is the same as the answer in any other significant chronic pain syndrome: the absence of a demonstrable lesion does not confirm the diagnosis of psychogenic pain, and the presence of psychopathology does not mean that the patient is not suffering. Although our intellectual grasp of nociceptive systems is good, these systems are not sufficient to explain all types of pain. Chronic pain must be viewed as a biopsychosocial phenomenon.
4
Some patients who had clearly defined causes for back pain continue to suffer from the same pain, even after the causative agent is eliminated. Why?
There is evidence to suggest that chronic, ongoing pain can actually restructure signaling within the central nervous system. There are synaptic changes and there may be neuronal hyperactivity, expression of new genes, and other central phenomena that perpetuate the perception of pain.
5
What characteristics of pain help to define its origin?
The type of pain suffered varies with the structure involved. Pain originating in a vertebral body (from osteoporosis, tumor, or infection) tends to be local and aching. It is somatic, nociceptive pain, made worse by standing or sitting and relieved by lying supine. Even though it is usually local, it may refer to other sites. Characteristically, the L1 vertebral body refers pain to the iliac crests and hips. When facet joints are involved, pain is most pronounced when the back is extended. Limitation of active range of motion is a hallmark of facet pain.
6
How do the intervertebral discs (“slipped discs”) contribute to back pain?
The intervertebral disc is composed of a firm anulus fibrosus, with a spongier nucleus pulposus inside. The fibrous ring is innervated by nociceptors, but the nucleus pulposus is not. When strong vertical stress is applied to the spine, the nucleus pulposus bulges outward through the anulus fibrosus. Stretching of the fibrous ring is painful; in general, it produces localized low back pain. Once the anulus breaks, disc material may extrude and press against a nerve. Pressure on the nerve root is felt as radicular pain (“sciatica”). Of interest, as the anulus bursts, the intense low back pain tends to subside and is replaced by radicular pain.
A bulging disc in itself is usually not painful. Anything that increases pressure on the spine increases pain from a disc. Thus, pain is exacerbated by standing, sitting, and the Valsalva maneuver.
7
What is the usual outcome of a patient with acute low back pain?
The vast majority of the general population will have acute back pain at some point in their lives. Over 90% of cases resolve, without specific therapy, in less than 2 weeks. As mentioned earlier, in most cases no specific diagnosis is made.
8
How helpful are radiographs in determining the etiology of acute low back pain?
Most patients with acute low back pain require no imaging procedures. It may not be easy to convince a patient who is writhing in pain that no radiographs are needed. However, plain radiographic findings of degenerative disease are as common in asymptomatic patients as in patients with acute back pain. Furthermore, magnetic resonance imaging (MRI) is far too sensitive and nonspecific to be used as a screening procedure. More than one half of adults with no history of back pain may show asymptomatic bulging of discs at one or more lumbar levels, and fully one fourth show disc protrusion.
Reserve imaging procedures for patients with acute low back pain when the diagnosis is in question. Specifically, if fever or point tenderness on the spine raises the suspicion of infection or tumor, an imaging procedure is imperative.
9
A patient complaining of left lower back pain stands with his buttocks protruding and with his shoulders tilted to the left. What does this stance indicate?
The spine has a number of normal curvatures. With the patient standing erect, the normal position of the spine shows cervical lordosis, thoracic kyphosis, and lumbar lordosis. In low back pain with muscle spasm, the lumbar lordosis may be lost or hyperaccentuated. If the patient tilts toward one side, there may be muscle spasm or foraminal encroachment. With lateral tilt, the ipsilateral intervertebral foramen narrows. Therefore, if there is nerve root compression in the foramen, pain increases. Conversely, when the patient tilts away from an affected side, the foramen on that side opens, lessening neural pain but possibly accentuating pain from muscle spasm. In lateral disc herniations, patients tend to lean away from the side of the herniation.
10
What is the normal range of motion of the spine?
The lumbar spine should be able to flex forward 40 to 60 degrees from the vertical. As the patient extends backward, range is somewhat reduced (to about 20 to 35 degrees). Severe pain on extension of the spine may indicate pathology in the articular facets.
11
Describe the significance of the straight-leg raising maneuver
Straight-leg raising is used to diagnose nerve root compression from disc disease. It is most commonly used to look for lower lumbar root pathology. The patient lies supine, and the leg is elevated from the ankle, with the knee remaining straight. Normally, patients can elevate the leg 60 to 90 degrees without pain. In disc herniations, elevations of 30 to 40 degrees produce pain.
Ipsilateral straight-leg raising is more sensitive, but less specific, than contralateral straight-leg raising. That is, nearly all patients with herniated discs have pain on straight-leg raising on the affected side, but straight-leg raising elicits pain in many other conditions (e.g., severe hip arthritis). However, contralateral straight-leg raising does not produce pain on the affected side unless the pain is due to root disease.
Use Patrick's maneuver to differentiate between hip and lumbar root pathology. The thigh is flexed on the abdomen and the knee is externally rotated, putting stress on the hip joint but not on the nerve root. The patient with hip pathology experiences pain, but the patient with root pathology does not.
12
What is the significance of pain on percussion of the spine?
Benign disease (disc protrusion and muscle spasm) rarely, if ever, produces pain on percussion of the spine. This sign usually indicates bone disease, most often metastases or infection; it requires immediate investigation with imaging procedures.
13
What historical data raise suspicion of infection or tumor, rather than benign disease?
Most patients with herniated discs or other benign mechanical causes of back pain state that the pain improves with bed rest. When they are no longer weight bearing, pain is relieved. Patients with tumor or infection often say that their worst pain is at night when they are in bed. Nocturnal exacerbation is a clear danger signal.
14
Describe the most common scenario for a herniated intervertebral disc
In the most common scenario for a herniated intervertebral disc, patients report severe back pain after lifting something heavy, and a few days later pain radiates down the leg. This sequence of events is due to the pathologic process underlying a herniated disc. With the initial exertion, the nucleus pulposus pushes against the anulus fibrosus, causing it to distend. This distention causes local back pain. As the anulus ruptures, the back pain is relieved, but the nucleus then presses against a nerve root, causing radiated pain down the leg.
15
What is the most common symptom for vertebral metastases?
Patients with vertebral metastases almost invariably experience localized back pain. More than 95% of patients with malignant epidural spinal cord compression have pain as their first complaint. Pain is usually described as deep, localized, and aching. As neural structures become involved, the pain radiates in the distribution of the affected nerves. The thoracic spine is the site most commonly affected; thus, pain radiates in a band around the chest. Over time, further neurologic problems ensue. If epidural spinal cord compression progresses, patients have paraparesis, sensory loss, and bowel and bladder involvement. Epidural spinal cord compression from tumor is a medical emergency.
Pain usually resolves fairly quickly with the administration of high doses of dexamethasone. Definitive treatment with radiation therapy or surgery is then undertaken.
16
Describe the radiographic appearance of spinal metastases
On plain films, one of the earliest signs of spinal metastasis is erosion of a pedicle. Over time, the vertebral body begins to lose height. MRI reveals a change in signal intensity in the vertebral body. As the tumor progresses, it may be seen invading the epidural space and compressing the spinal cord.
17
Both vertebral metastases and vertebral osteomyelitis can cause destruction of vertebral bodies and changes on MRI signal. How can they be differentiated?
When tumors affect the vertebral bodies, they tend to spare the disc spaces. Even though two or three adjacent vertebral bodies may be destroyed by tumor, the disc spaces between them are generally preserved. In the case of vertebral osteomyelitis, the disc space typically is destroyed by the infection, and the adjacent vertebral bodies appear to form a block of infection.
18
What is the difference between an osteoporotic vertebral collapse and vertebral collapse caused by tumor involvement?
Clinically, the pain from an osteoporotic collapse is almost invariably relieved by a brief period of bed rest. Tumor-related pain is often unrelieved by bed rest.
Pathologically, an osteoporotic collapse is essentially an accordion of the vertebral body. A hollow body collapses on itself. With tumor involvement, collapse of the vertebral body causes extrusion of tumor material.
Tumor extrusion may compress the spinal cord. Compression from osteoporosis is exceedingly rare.
19
What treatment should be used for the pain from metastatic destruction of a vertebral body?
Pain from vertebral metastases is due to destruction of bone trabeculae, expansion of the periosteum, and stretching of the dura. This is a classic somatic nociceptive pain syndrome. As such, it is well treated by a combination of either nonsteroidal antiinflammatory drugs (NSAIDs) or steroids and an opioid. As bone metastases grow, they elaborate prostaglandin E 2 , which continues destruction of bone trabeculae. The administration of an NSAID or steroids decreases production of prostaglandin E 2 and slows destruction.
20
Why is osteoporosis painful?
In general, osteoporosis is not painful in the absence of fractures. In weight-bearing bones, microfractures can occur with minor trauma. Unfortunately, the patient with this type of pain generally stays in bed, and the absence of weight bearing leads to further demineralization of the bone and additional fractures upon weight bearing. In such patients, progressive exercise is of paramount importance. Weight bearing leads to greater bone density and fewer fractures. Of interest, when a vertebral body collapses completely, it is painful at first, but the pain subsides once the fracture is complete.
21
How should pain from an osteoporotic vertebral collapse be treated?
First, be sure that the pain is due to benign osteoporotic collapse. Although postmenopausal women and patients treated with corticosteroids are at high risk, do not assume that the osteoporosis is idiopathic. Evaluate serum protein electrophoresis, sedimentation rate, alkaline phosphatase, phosphorus, serum calcium, and plain films to rule out a secondary cause for the osteoporosis. Once a secondary cause has been ruled out, treat the patient with therapy directed at reversing the osteoporosis and with analgesics and exercise. Vertebroplasty and kyphoplasty are radiologic procedures for the treatment of the intense pain caused by vertebral compression fracture when the pain has been inadequately controlled with more conservative means. Each procedure involves the intraosseous injection of acrylic cement under local anesthesia and fluoroscopic guidance to control the pain of vertebral fractures associated with osteoporosis.
22
What is the most common symptom of vertebral osteomyelitis?
A patient with vertebral osteomyelitis usually has subacute back pain that increases over days to weeks. Progressive pain is felt in the low back and, if untreated, focal weakness and bowel and bladder problems ensue. Focal tenderness is present, and usually another source of infection is found. Although previously the most common incidence was in the lumbar spine in men over age 50, the AIDS epidemic has changed the epidemiology somewhat. Younger men are affected, and the cervical spine is becoming a more common site of vertebral osteomyelitis.
23
What is the most common cause of vertebral osteomyelitis?
In immunocompetent hosts, Staphylococcus aureus infection is the most common causative agent. Infection involves the vertebral bodies, endplates, and disc spaces, but generally spares the posterior elements. In the rare cases of actinomycosis or coccidioidomycosis, the posterior elements may be involved, and the spine becomes unstable.
24
What is sciatica?
The term sciatica has come into rather broad usage and usually refers to any sharp pain that radiates down the posterior aspect of the leg. Its initial formulation was for pain in a sciatic nerve distribution. However, it is used to describe pain of L5 root compromise, S1 root compromise, and true sciatic neuropathy.
25
What is piriformis syndrome?
The sciatic nerve passes through the piriformis muscle as it exits the pelvis. Occasionally, the muscle has a fibrous band or area of contraction. Pain is felt in the distribution of the sciatic nerve, but there is no back pain. Pain radiates from the buttocks down the posterior aspect of the thigh. Deep palpation of the piriformis muscle, either through the buttocks or through a rectal examination, exacerbates the pain and reproduces the patient's clinical syndrome. Therapy involves repeated stretching of the piriformis muscle or, in extreme cases, injection of lidocaine and steroids into the piriformis.
27
If a patient has severe back pain radiating into the anterior thigh accompanied by weakness of the leg, how can you differentiate between an L4 radiculopathy and a femoral nerve lesion?
The L2, L3, and L4 roots split into anterior and posterior divisions. The anterior divisions come together to form the obturator nerve, and the posterior divisions come together to form the femoral nerve. The quadriceps muscle is innervated by the femoral nerve, and the adductors of the thigh are innervated by the obturator nerve. In an L4 radiculopathy, both the quadriceps and the adductors are affected. In a femoral nerve lesion, the quadriceps are affected, but the adductors are spared.
30
What is the role of MRI in the diagnosis of herniated discs?
The MRI scan is highly sensitive for disc pathology. Even slight bulges in the disc can be picked up with an appropriate MRI; however, it may be overly sensitive. The fact that a disc is seen to be bulging or herniated on MRI does not mean that it causes the pain syndrome. Nearly one half of a sample of asymptomatic patients was shown to have disc bulges on MRI. The advantage of MRI over computed tomography (CT) scan is that the nerve root can be seen.
31
In a patient with low back pain and a previously operated-on herniated disc, how can you differentiate between a new disc herniation and scar tissue?
Differentiating between a new disc herniation and scar tissue can be a particularly vexing clinical problem. On MRI scan, discs do not enhance with gadolinium, but inflammatory tissue may.
32
If a patient has acute low back pain and there are no findings on clinical examination, how much bed rest is required?
No evidence indicates that bed rest influences the ultimate outcome of low back pain. In general, patients with acute pain feel more comfortable with a day or two in bed. However, more prolonged bed rest leads to deconditioning and may prolong recovery time (see Questions 20 and 49).
33
What weight of traction should be used for low back pain?
The theoretical benefit of traction is to lower intradiscal pressure. Simply lying supine reduces pressure, and no evidence indicates that traction significantly alters the outcome of low back pain. Traction from 5 pounds to total body inversion has been used without clear demonstration of lowering pressure beyond the levels achieved by recumbency.
34
Describe the role of myelography in low back pain
Myelography has been almost completely supplanted by MRI scanning in low back pain. However, in cases in which the exact location or morphology of a disc herniation is in doubt, myelography can be combined with CT scanning to provide exquisite anatomic images.
35
What is meant by a facet syndrome?
The articular facets are the means by which the vertebral bodies articulate with each other. When these joints become inflamed or arthritic, range of motion is diminished. Maximal stress is put on these joints when the spine is hyperextended. Thus, when the patient reports no pain on anterior flexion, but severe pain on extension, a facet syndrome is believed to be present. The diagnosis is confirmed by CT scanning of the affected area with demonstration of marked arthritic changes of the specific facet. In some patients, direct instillation of a steroid solution and lidocaine into the affected facet produces dramatic relief.
37
What is spondylolisthesis?
Spondylolisthesis refers to slippage of one vertebral body on the adjacent one. It is fairly common in the older person (10% to 15% of even asymptomatic patients over the age of 70). Most cases are caused by lysis of the posterior elements, which may be due to advanced age or trauma. When pain is markedly exacerbated by movement, imaging should be performed with flexion and extension views, which show whether there is any increase in movement at the abnormal joint.
38
What is meant by a lateral recess syndrome?
The lumbar spine contains a triangular space (the lateral recess) bordered by the pedicle, vertebral body, and superior articular facet. Facet hypertrophy or a disc fragment may encroach upon this triangular space and compress a nerve root on its way to exit at the next lower level. Pain is often neuropathic and is characterized by lancinating jabs or by a burning, dysesthetic pain in the distribution of the affected nerve root.
39
Define lumbar arachnoiditis
Lumbar arachnoiditis refers to thickening of the arachnoid lining around the nerve roots. It is most commonly iatrogenic, produced by repeated myelography or by surgery. Nerve roots may become matted in an inflamed arachnoid or by scar tissue. On MRI, the nerve roots appear matted together. They may form a clump in the center of the canal or be matted to the sides of the canal.
40
What is spinal stenosis?
Spinal stenosis is a narrowing of the spinal canal. Facet hypertrophy, ligamentous hardening, and spondylolisthesis can narrow the diameter of the lumbar canal as a result of normal aging. In some cases, this may lead to a syndrome called neurogenic claudication, in which patients are pain-free at rest, but develop pain upon walking. The pain is felt as an ache in both legs. Patients characteristically say that they get relief after stopping for a few minutes and leaning forward at the waist. According to one theory, compromise of the radicular arteries gives rise to the claudication.
41
What is the role of epidural steroid injections in low back pain?
There are not enough well-controlled clinical trials in select patient populations to define accurately the indications for epidural steroid injection. However, clinical experience shows that many patients have dramatic responses. A small amount of a corticosteroid is mixed with a small amount of lidocaine, and the mixture is instilled into the epidural space. Patients report early pain relief from the lidocaine, exacerbation of pain in the evening, and then gradual diminution of pain as the steroids take effect. In good hands, epidural steroid injections are a relatively low-risk procedure. In any case, no more than three injections should be performed in any 6-month period, because epidural steroid injections may lead to ligamentous laxity.
42
What are the indications for laminectomy and discectomy?
The indications are open to great dispute. Some surgeons believe that the only cure for lumbar radiculopathy is surgical removal of the causative disc. However, in many cases of low back pain, the herniated disc may not be the causative factor. A conservative approach dictates that progressive pain with neurologic impairment is an indication for surgical intervention.
44
Why is there no definitive answer about the benefit of surgical procedures that have been performed for decades?
The problem lies in a number of areas. An appropriate study of laminectomy and discectomy would have to control for the cause of back pain, anatomical location, surgical procedure performed, neurologic and psychological status of the patient, skill of the surgeon, intensity of pain, compounding social factors, duration of pain, and specific criteria for outcome. This study would have to be prospective, involve a large number of patients, and have a sham surgery control. Such a study would be prohibitively expensive and have a number of ethical issues.
45
Is transcutaneous electrical nerve stimulation (TENS) effective in low back pain?
Here again, studies have yielded conflicting results. In a large metaanalysis, a definitive statement could not be made. When TENS is compared with inactive placebo, it appears to have an effect. However, an appropriate control would have to deliver some type of stimulus. Much the same can be said for acupuncture.
46
What are the recent surgical innovations in the treatment of lumbar disc disease?
Surgical interventions are becoming “less invasive.” Some of the newer techniques include intradiscal electrothermal therapy (IDET), radiofrequency ablation (RFA), percutaneous endoscopic laser discectomy (PELD), and cryoablation. These are all aimed at removing or repairing disc material, without the need for extensive laminectomies.
47
What is the role of acupuncture in low back pain?
A systematic review of the literature recently updated a prior study. Because acute low back pain tends to be self-limited, firm conclusions could not be drawn regarding the efficacy of acupuncture in that setting. For chronic low back pain, it did seem to show some advantages for pain relief and functional improvement in the short term. In the current context, given the lack of well-controlled studies, acupuncture should probably be viewed as a useful adjunct to other therapies in chronic low back pain.
48
What is the role of exercise in low back pain?
Individually tailored exercise programs, aimed at stretching, strengthening, and general conditioning, may improve pain and function in chronic low back pain, when the exercises are supervised by a trained individual. The exact characteristics of the exercise pattern that best treats low back pain have not been elucidated.
49
What is the role of prolonged bed rest in low back pain?
There is no evidence to suggest that bed rest of more than 2 days is beneficial. In fact, for people with acute low back pain, bed rest may be less effective than staying active. There is little or no difference in outcome in patients with sciatica.
50
What is the best method for treating acute and chronic low back pain?
Systematic reviews have covered areas as diverse as psychological interventions and extensive surgical exploration with instrumentation. Almost invariably, these studies end with the phrase “further studies with adequate controls are required for definitive statement.”
51
What phrase most clearly demonstrates that we do not fully understand the relative indications of specific treatments for low back pain?
“Further studies with adequate controls are required for definitive statement.”
- 1 Most cases of acute low back pain are not associated with a clearly defined pathophysiologic mechanism, and most resolve spontaneously. In most cases imaging is not required for patients with acute low back pain.
- 2 Chronic low back pain is associated with many known causes, including degenerative disc and joint disease, neoplasm, osteoporosis, and infections, but frequently a known cause cannot be determined.
- 3 Numerous treatments are available and should be considered for patients with chronic low back pain. Treatment should be individualized to the patient's needs and specific circumstances.
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