Low Back Pain: Where Does It Come From And How Do We Treat It?

Gregory C. Keller, M.D.
Gregory Keller, M.D. is an Orthopedic Surgeon with the Jacksonville Orthopedic Institute.

Lower back pain is the most common musculoskeletal complaint and is one of the most common reasons for medical evaluation.¹ Approximately 80% of the adult population will suffer from pain related to the lower back during their lifetime. Fortunately, the condition is usually self-limiting and thus rarely requires more than reassurance and possibly a short course of analgesics. Despite the typically benign course, problems related to the lower back account for greater than 14 billion dollars a year in direct medical costs and significantly more in lost wages and productivity.² Males between the ages of 35 to 45 are most at risk but the association between the kind of work (e.g. manual labor) and back pain is less clear. This article will explain the cause of much lower back pain and outline the most appropriate evaluation and nonoperative treatment methods.

Degenerative Disc Disease

The lumbar spine is made up of five (although there are exceptions) vertebral bodies. Each of these is connected to its two neighboring bodies by facet joints posteriorly and an intervertebral disk between the vertebral bodies themselves (Figure 1). The disk is composed of a tough outer annulus surrounding a soft center called the nucleus pulposis -- the analogy of a jelly doughnut or radial tire is often used (Figure 2). Biomechanically, the disk works by converting axial loads applied through the nucleus into tensile loads that are resisted by the annulus. As we age, the annulus becomes more friable and is subject to cracking and fissures called annular tears. Since the annulus is highly innervated these tears are often painful. This is known as degenerative disc disease. Although we will all suffer from degeneration of our intervertebral discs, some of us will be spared from suffering pain. Although the reason for this is unclear, it has been postulated that about one-third of the population does not have innervation of the outer annulus and thus will feel no pain.³

Figure 1. The vertebral bodies (¬) are separated by the disc (ð). The facets (®) constitute the posterior connection between two bodies. The pars interarticularis (Ø) connects the facet above to the facet below.	Figure 2. The disc is composed of the tough outer annulus surrounding a soft nucleus pulposis.

The patient will typically present with complaints of lower back pain only, but can also experience radiation into the gluteal region, groin, or proximal thighs. This pain is often made worse by sitting and relieved with recumbence. Activity may actually provide some relief but certain tasks such as lifting will exacerbate the symptoms. Women may experience increased pain just prior to their menstrual cycle.

There will often be a history of an acute onset related to lifting or turning. A family history of back trouble is common. The duration of the symptoms is important since most cases of acute lower back pain resolve within eight to twelve weeks. Pain lasting longer than this is usually related to a degenerative condition of the disc or facet joints as opposed to a muscle strain. Although common, muscle strains will typically resolve within a few weeks. The physical exam should include an assessment of spinal range of motion and a focused neurologic exam of the lower extremities. Typically the patient will move slowly and painfully and the neurologic exam will be normal.

Radiographs are not necessary during the first few weeks unless there are "red flags" present (see Table 1). Magnetic Resonance Imaging (MRI) can be useful in identifying a degenerative disc but should be reserved for refractory cases (Figure 3) or where it is important to rule out other potential problems such as malignancy or infection.

Figure 3. Magnetic Resonance Image (MRI) of the lumbar spine. A sagittal t-2 weighted image demonstrating the severely degenerative disc (Ø). Note the reaction of the bone marrow on either side of the disc (Modic changes) (¬).

Most of these problems can be managed with non-steroidal anti-inflammatories and occasional narcotics. Physical therapy is appropriate for pain that lasts more than a few weeks. A four to six week program that emphasizes strengthening of the back and abdominal muscles seems to provide the greatest benefit. The patient should receive some education as to the cause of the problem as well as the most appropriate way to lift, sleep, etc. Surgery should be reserved for the rare patient who continues to have disabling back pain despite six months of aggressive conservative treatment. Since the pain is secondary to motion at a painful degenerative disc, surgery usually entails fusing the two vertebral bodies together to eliminate the motion. It is currently felt that a fusion between the vertebral bodies themselves gives the most predictable pain relief since this provides rigid immobilization of the annulus. Despite the advances in the surgical care of lower back problems it should be emphasized that the great majority of patients suffering from chronic lower back pain can and should be treated nonoperatively. Furthermore, even a successful fusion does not guarantee complete relief of pain. Sometimes the reasons for failure are evident (e.g. a pseudarthrosis or nonunion) but often no clear explanation is found. The patient must understand this before undergoing surgical treatment.

Radicular Pain And Sciatica

Occasionally the continued loading of a degenerative disk can force some of the nucleus through a tear in the annulus (Figure 4). This is a herniated nucleus pulposis or HNP and if this occurs in a posterior direction (most common), then the nuclear material can come to lie next to the passing nerve root. We know that the contents of the nucleus are inflammatory and thus contact with the nerve root will often cause pain in the distribution of that nerve. If there is no significant compression of the nerve then there may not be any objective findings on exam; only the complaint of pain shooting or radiating down the leg and often into the ankle or the foot. This should be differentiated from a radiculopathy where there is objective evidence of nerve dysfunction. A large herniated disc can compress multiple nerve roots thus affecting bilateral leg, bowel, and bladder function. Known as cauda equina syndrome, this is a rare but serious condition and demands urgent intervention in the form of surgical decompression.

Figure 4. A drawing of a disc with the nuclear material herniating out through a tear in the annulus.

The patient suffering from sciatica will complain of pain radiating down the leg and often into the foot. This typically affects only one leg although bilateral involvement is possible. The patient may complain of numbness in the same distribution. Weakness is less common but can be significant and can cause a limp. The history will often include back pain that subsided just before the onset of leg pain. Complete bed rest may provide some relief.

The physical exam must include a neurologic assessment to rule out a significant radiculopathy. This should include reflexes (knee and ankle jerks), sensation, and strength testing. An understanding of the specific dermatomes and muscles innervated by the individual nerve roots can help localize the level of the herniation. Tension signs such as a positive straight leg-raising test are indicative of nerve compression.

Radiographs are rarely helpful beyond showing some early degenerative changes. If there is a neurologic deficit or if the symptoms have persisted beyond 4 - 6 weeks then an MRI is appropriate since this can demonstrate the pathology (Figure 5). Although sensitive, the MRI is not very specific. At least 30% of asymptomatic people older than 30 years will demonstrate some abnormality on an MRI scan of their lumbar spine.⁴

Figure 5. A sagittal T-1 weighted image demonstrating the disc herniation posteriorly (ð) which displaces the thecal sac (®).

Non-steroidal anti-inflammatory medication and appropriate analgesics are the mainstay of early treatment. A seven-day course of steroids (Medrol dose pak®) is often extremely helpful in the more severe cases as is injections of steroid into the space surrounding the nerve root (epidural steroid injection). Most of these patients will begin to improve within a few weeks and approximately 90% will be better in six to twelve weeks due to lessening of the inflammatory reaction and resorption of the disc fragment. Surgery is reserved for severe symptoms that persist beyond this six weeks or for cases where there is progressive and significant muscle weakness. The results of surgical intervention are greater than 90%, with good to excellent and recovery usually complete within four weeks. It should be remembered that surgery is intended to relieve only the leg pain and approximately 20% of patients will have persistent back pain related to the underlying degenerative disc disease.

Spinal Stenosis And Neurogenic Claudication

Spinal stenosis occurs when the canal through which the nerves pass becomes narrowed secondary to degenerative changes in both the disc in front and the facet joints in the back of the spinal canal. This affects the nerve roots by limiting the blood supply and venous drainage. Symptoms occur with activity since the blood supply to the involved nerves is insufficient to meet the increased demand. This leads to neurogenic claudication.

The patient presenting with neurogenic claudication will typically be older (sixth or seventh decade of life) and complain of pain in the legs after walking. They may also suffer symptoms upon recumbence and this may interfere with their sleep. Sitting exercise on a stationary bike and walking slightly bent forward (pushing a grocery cart) relieves the stenosis and is better tolerated.

During the history taking the clinician should ask about activity related pain. The patient will often describe symptoms in both legs that are relieved with sitting. The neurologic exam will usually be normal and there will not be any root tension signs. The exam must include a vascular evaluation including an assessment of peripheral pulses.

Plain radiographs will often demonstrate severe degenerative changes throughout the lumbar spine. Magnetic resonance imaging will confirm the diagnosis but a lumbar myelogram remains the gold standard for accurately revealing the severity and location of the pathology.

Initial management can include anti-inflammatory medications, a light aerobic exercise program and analgesics. Epidurals are also useful in managing the pain but the symptoms usually return. Surgical decompression of the spinal canal gives predictable long-term relief. This typically involves removing the compressive structures such as osteophytes and part of the enlarged facet joints. Occasionally a fusion is required to prevent recurrence or instability.

Spondylolysis And Spondylolisthesis

An isthmic spondylolysis is a developmental fatigue fracture of the pars, which typically occurs during childhood. A spondylolisthesis indicates a slippage of one vertebral body on another secondary to this lesion in the pars. Although relatively common, most will remain quiescent until the third or fourth decade of life when some slight trauma will trigger an onset of pain.

These patients will present in a similar manner to those suffering from degenerative disc disease. They will complain of mechanical-type lower back pain that is relieved with rest. Occasionally they will complain of leg pain if a nerve root becomes trapped under the scar tissue that surrounds the pars lesion. The exam will be unremarkable except for limited range of motion and hamstring tightness. A neurologic deficit is seldom discovered.

Plain x-rays will demonstrate the lesion in the pars and the listhesis (Figure 6). Oblique films are often helpful and a CAT (computer-assisted tomography or CT) scan can confirm the presence of the lesion. An injection of lidocaine into the area can temporarily relieve the pain thus demonstrating that this is the problem.

Figure 6. The slippage associated with a spondylolisthesis is apparent on this lateral x-ray of a lumbar spine. The posterior borders should ordinarily line up. The pars defect is denoted by a (ð). The two lines denote the posterior border of L5 and S1 respectively. Normally they would be in line.

The mainstay of treatment for this condition is an exercise program that emphasizes abdominal strengthening. Combined with weight control, this will be successful in the majority of patients. Surgery is indicated in the patient who has disabling pain despite conservative care and who understands the risks and limitations of surgical care. The surgical treatment of this problem involves fusing the motion segment to prevent motion and pain. An alternative approach is to mend the lesion itself through grafting of the pars defect. This should be reserved for the younger and more active patient who can benefit from retaining the motion through that segment.

Tumors And Infection

Neoplasms involving the spine typically are metastatic lesions from distant primary tumors. Lung, prostate, breast, renal, and thyroid tumors can all spread to the spine. Primary tumors of the spine are rare with the exception of plasmacytoma and multiple myeloma. Infections usually begin in the disc space and spread to the vertebral body or to the epidural space. Although rare in healthy individuals, infections of the spine can occur in the immunocompromised patient and can be a complication of spinal surgery.

Night and rest pain are hallmarks of neoplastic or infectious disorders and all patients presenting with back pain should be asked about this and about a history of cancer, fever or unintentional weight loss. Any of these should alert the clinician to the possibility of a neoplasm or infection.

Plain radiographs can often demonstrate bone destruction secondary to a neoplasm or infection but the MRI is the most sensitive study available and can usually discriminate between an infection and tumor versus a degenerative process. The most notable exception to this is the acute compression fracture that cannot easily be distinguished from a neoplastic process during the first six to eight weeks.

Surgery for metastatic disease is reserved for those cases where there is spinal instability or neurologic compromise and at least a three to six month life expectancy. Infection involving the disc can often be treated with intravenous antibiotics after aspiration under x-ray guidance. If the infection forms an abscess then surgical drainage is appropriate. If this abscess compresses the neurologic structures (spinal cord or cauda equina) then decompression and drainage is often essential to preserve neurologic function so a surgical consultation should be obtained on an emergent basis.

Nonspinal Causes Of Lower Back Pain And Sciatica

Nonspinal causes of lower back and radicular pain are relatively common and should always be considered in the differential diagnosis. These include piriformis syndrome, sacroilitis, trochanteric bursitis, and coccydynia. Piriformis syndrome involves swelling and spasm of the piriformis muscle that crosses over the sciatic nerve in the pelvis. This condition can mimic sciatica from a discogenic source.⁵ Sacroilitis describes pain evolving from the sacroiliac (SI) joint and the diagnosis can be confirmed by injecting the SI joint under fluoroscopic guidance with a short acting analgesic. Trochanteric bursitis is a common condition and presents with lateral hip pain which can radiate down to the knee. An injection of Lidocaine and steroid into the area of maximum tenderness can give long term relief; surgery is usually not necessary. Coccydynia describes chronic pain relating to the coccyx and its supporting ligaments. This is usually easily diagnosed on physical exam since there will be tenderness over this area. An injection into the coccyx and the ligaments guided by a finger in the rectum can give temporary relief. If this and a "doughnut" seat are unable to control the symptoms then surgical resection is an option.

Referral Alternatives

Currently there appears to be two options in the management of benign chronic lower back pain (with or without leg pain) that is refractory to the initial conservative interventions and thus is being considered for referral. Orthopaedic and neurosurgical spine specialists are generally interested in trying to discover and treat the source of the pain thus hopefully eliminating the painful lesion. This often involves surgery and thus can be very intimidating for the patient. This is especially true since the history of back surgery is fraught with failures. Nevertheless, appropriate surgery directed at a structural lesion and/or a pain generator site should offer the patient an 80-90% chance of being markedly improved.

Pain Management is an alternative to surgery that is growing in popularity. It is appealing since it usually does not involve any significant surgery and is usually successful in helping to manage the pain and improving function. The emphasis here is not to find the source of the pain but to treat the pain itself. This is most appropriate for the patient whose problem is not amenable to surgical repair or for those who do not wish to have surgery and whose pain is refractory to other types of conservative management. This kind of intervention gives only temporary relief requiring repeat treatments on an ongoing basis.

The management of lower back pain has improved significantly over the past few years but can still be a source of frustration for both the physician and the patient. It should be remembered that lower back pain is typically a degenerative condition involving the whole spine and as such is rarely amenable to a "cure". The condition will invariably progress at other levels and future problems are to be expected. Current treatment protocols are a result of experience and training since dependable "evidence based" treatment guidelines are not yet available.⁶ Most of these problems can be managed successfully by a primary care provider and referral to a specialist is indicated when there is evidence of neurologic compromise, a neoplastic process, an infection or the symptoms persist beyond two to three months despite treatment as outlined above.

REFERENCES

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2. Akeson WLT, Murphy RW. Low Back Pain. Clin Orthop. 1977; 129: 2-3.
3. Kuslich S. Personal communication, 1996.
4. Boden SD, Davis DO, Dina TS, Patronas NJ, Wiesel SW. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects: A prospective investigation. J Bone Joint Surgery. 1990; 72(3): 403-8.
5. Weiss HB. Non discogenic low back pain. Jacksonville Medicine. 1992; 43(12) 533-535.
6. U.S. Department of Health and Human Services, Agency for Health Care Policy and Research, Acute Low Back Problems in Adults, Publication No. 95-0642 December 1994 phone: (202) 512-1800 for reprints.

Jacksonville Medicine / April, 1999