Essentials of Orthopedic Surgery, third edition / 07-The Spine

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FIGURE 7-7. This metrizamide myelogram illustrates a large central disk herniation at the L4–L5 level. (A) Anteroposterior and oblique views reveal this prominent defect more marked on the right. (B) This lateral view illustrates a “doubledensity” prominent ventral indentation of the dye column. (From Rothman RH, Simeone FA. The Spine, 2nd ed. Philadelphia: Saunders, 1982, reprinted with permission.)

zamide, the oil-based agent Pantopaque had a much higher incidence of complications and was known to cause a crippling arachnoiditis. Newer contrast agents are now available that are reported to have fewer side effects.

Computed Tomography

Computed tomography is a very versatile and widely available noninvasive modality for evaluating abnormalities of the lumbosacral spine. Multiple cross-sectional (axial) images of the spine are made at various levels and, with reformatting, coronal, sagittal, and three-dimensional images may be created. The CT scan demonstrates not only the bony spinal configuration, but also the soft tissue in graded shading, so that ligaments, nerve roots, free fat, and intervertebral disk protrusions can be evaluated as they relate to their bony environment (Figs. 7-8, 7-9).

The CT scan is an extremely valuable diagnostic tool when it is used appropriately to confirm the patient’s clinical findings. However, recent studies reveal the pitfalls of making clinical decisions on the basis of isolated CT scan findings. Despite many reports in the literature indicating that CT scanning has a mean accuracy of 90% in symptomatic patients, 34% of asymptomatic patients had abnormal CT scans when reviewed by

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three independent expert interpreters. The implication is that a patient with a negative history and physical examination for a spinal lesion has a one-in-three chance of having an abnormal CT scan. If the decision for surgery is based only on scan results, there is a 30% chance that the patient will undergo an unnecessary and unsuccessful operation. However, if the patient’s clinical picture correlates with the CT scan abnormalities, CT can be a useful confirmatory diagnostic tool.

Electrodiagnostic Testing

The EMG is performed by placing needles into muscles to determine if there is an intact nerve supply to that muscle. An abnormal EMG can demonstrate impaired nerve transmission to a specific muscle and isolate the nerve root involved. Initially, the EMG will be negative in spite of nerve entrapment and only show muscle irritability. After 3 weeks of significant pressure on a nerve root, signs of denervation with fibrillation can be observed.

The EMG, similar to all the other confirmatory tests already discussed, is not a screening tool. In fact, when dealing with the average low back problem, the EMG rarely provides any information that cannot be derived from a careful physical examination. It may even confuse the picture, because an EMG may be abnormal from diabetic neuropathy, previous peripheral nerve entrapment, or trauma. In cases in which the correlation of clinical signs and imaging is equivocal, especially with chronic unexpected sciatica, nerve conduction studies and EMG may be helpful. Electromyography can also detect the involvement of a secondary nerve root in cases of complex back injury preoperatively, sometimes prompting a more-extensive operation.

Clinical Conditions

There are a number of conditions that can present as low back pain in any particular individual. However, the following four, the most common of those typically evaluated by orthopedic surgeons, are discussed in detail: back strain, herniated disk, spinal stenosis, and spondylolisthesis.

Back Strain–Lumbago

The vast majority of people who have low back discomfort suffer from a nonradiating type of low back pain called back sprain or lumbago. The etiology is not always clear but is probably a ligamentous or muscular strain secondary to either a specific traumatic episode or the continuous mechanical stress of a postural inadequacy. These patients may also include those with a small tear in the annulus fibrosus, which would account for the frequent prior history of low back pain in patients with a ruptured disk.

The main complaint of these patients is back pain, and it can be limited to one spot or cover a diffuse area of the lumbosacral spine. At times, there may be a referral of pain to the buttocks or posterior thigh because the lower back, buttocks, and posterior thigh all originate from the same embryonic tissue, or mesoderm. Such referral of pain does not necessarily connote any mechanical compression of the neural elements and should not be called sciatica.

The usual findings are limited to local tenderness over the involved area and muscle spasm; however, the attacks vary in intensity and can conveniently be divided into three categories: mild, moderate, and severe. Those placed in the mild group have subjective pain without objective findings and should be able to return to customary activity in less than a week. The moderate group is characterized by a limited range of spinal motion and paravertebral muscle spasm as well as pain, and these patients should be able to resume full activity in less than 2 weeks. The severe group includes those patients who are tilted forward or to the side. They have trouble ambulating and can take up to 3 weeks to become functional again.

Because a normal X-ray is a standard occurrence with a patient complaining of back strain, a radiographic study is usually not necessary on the first visit if the physician feels comfortable with the diagnosis; however, if the response to treatment does not proceed as expected, films should be taken to rule out other more serious problems such as spondylolisthesis or tumor. The authors’ usual recommendation is that if a patient fails to respond to conservative treatment for an acute attack of low back pain after a period of 2 weeks, then a routine lumbosacral spine X-ray series is clinically indicated.

The authors’ preferred treatment for low back strain is the functional restoration approach. The mainstay of treatment is controlled physical activity, with the judicious use of trunk flexibility and strengthening exercises as the acute phase subsides. Often, particularly in the obese patient with weak abdominal muscles, a lightweight lumbosacral corset is useful in helping to mobilize those encumbered by low back strain.

Herniated Disk

A herniated disk can be defined as the herniation of the nucleus pulposus through the torn fibers of the annulus fibrosus. Most disk ruptures occur during the third and fourth decade of life while the nucleus pulposus is still gelatinous. The perforations usually arise through a defect just lateral to the posterior midline where the posterior longitudinal ligament is weakest. The two most common levels for disk herniation are L4–L5 and L5–S1. These two disks account for 95% of all lumbar disk herniations; pathology at the L2–L3 and L3–L4 levels can occur, but is relatively uncommon.

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Disk herniations at L5–S1 usually compromise the first sacral nerve root. A lesion at the L4–L5 level most often compresses the fifth lumbar root, whereas a herniation at the L3–L4 more commonly involves the fourth lumbar root. It should be pointed out, however, that variations in root configuration as well as in the position of the herniation itself can modify these relationships. An L4–L5 disk rupture can at times affect the first sacral as well as the fifth lumbar root and, in extreme lateral herniations, the nerve ending exiting at the same level as the disk is involved.

Not everyone with a disk herniation has significant discomfort. A large herniation in a capacious canal may not be clinically significant because there is no compression of the neural elements, whereas a minor protrusion in a small canal may be crippling because there is not enough room to accommodate both the disk and the nerve root.

Clinically, the patient’s major complaint is pain. Although there may be a prior history of intermittent episodes of localized low back pain, this is not always the case. The pain not only is present in the back but also radiates down the leg in the distribution of the affected nerve root. It is usually described as sharp or lancinating, progressing from the top downward in the involved leg. Its onset may be insidious or sudden and associated with a tearing or snapping sensation in the spine. Occasionally, when the sciatica develops, the back pain may resolve because once the annulus has ruptured, it may no longer be under tension. Finally, the sciatica may vary in intensity; it may be so severe that patients are unable to ambulate and feel that their back is “locked.” Conversely, the pain may be limited to a dull ache that increases in intensity with ambulation.

On physical examination, there is usually a decreased range of motion in flexion, and patients will tend to drift away from the involved side as they bend. On ambulation, the patient walks with an antalgic gait, holding the involved leg flexed so as to put as little weight as possible on the extremity.

Although neurologic examination may yield objective evidence of nerve root compression, these findings are often undependable because the involved nerve is often still functional. In addition, such deficit may have little temporal relevance because it may relate to a prior attack at a different level. To be significant, reflex changes, weakness, atrophy, or sensory loss must conform to the rest of the clinical picture.

When the first sacral root is compressed, the patient may have gastroc- nemius–soleus weakness and be unable to repeatedly raise up on the toes of that foot. Atrophy of the calf may be apparent, and the ankle (Achilles) reflex is often diminished or absent. Sensory loss, if any, is usually confined to the posterior aspect of the calf and lateral side of the foot.

Involvement of the fifth lumbar nerve root can lead to weakness in extension of the great toe and, less often, to weakness of the everters and dorsiflexors of the foot. An associated sensory deficit can appear over the anterior leg and the dorsomedial aspect of the foot down to the great toe. There are usually no primary reflex changes, but, on occasion, a diminution

in the posterior tibial reflex can be elicited. The absence of this reflex, however, must be asymmetrical for it to have any clinical significance.

With compression of the fourth lumbar nerve root, the quadriceps muscle is affected. The patient may note weakness in knee extension, and it is often associated with instability. Atrophy of the thigh musculature can be marked. A sensory loss may be apparent over the anteromedial aspect of the thigh, and the patellar tendon reflex is usually diminished.

Nerve root sensitivity can be elicited by any method that creates tension; however, the SLRT is the one most commonly employed. As discussed previously, a positive test reproduces the patient’s pain down the leg. The reproduction of back pain is not considered positive.

The initial diagnosis of a herniated disk is generally made on the basis of the history and physical examination. Plain X-rays of the lumbosacral spine rarely add to the diagnosis but should be obtained to help rule out other causes of pain such as infection or tumor. Other tests such as the EMG, the computerized axial tomography (CAT) scan, and MRI are confirmatory by nature and can be misinformative when they are used as screening devices.

The treatment for most patients with a herniated disk is nonoperative because 80% of them will respond to conservative therapy when followed over a period of 5 years. The efficacy of nonoperative treatment, however, depends upon a healthy relationship between a capable physician and a well-informed patient. If a patient has insight into the rationale for the prescribed treatment and follows instructions, the chances of success are greatly increased.

One of the most important elements in the nonoperative treatment is controlled physical activity. Patients should markedly decrease their activity; this sometimes requires bed rest and in most cases can be accomplished at home. An acute herniation usually takes at least 2 weeks of significant rest before the pain substantially eases.

Drug therapy is another important part of the treatment, and three categories of pharmacologic agents are commonly used: antiinflammatory drugs, analgesics, and muscles relaxants or tranquilizers. Inasmuch as the symptoms of low back pain and sciatica result from an inflammatory reaction as well as mechanical compression, the authors believe that antiinflammatory medication should be taken in conjunction with rest. It should be stressed, however, that no medication can take the place of controlled physical activity. The patient’s pain generally is relieved when the inflammation is brought under control. There may be some numbness or tingling in the involved extremity, but this is usually tolerable.

Analgesic medication is rarely needed if the patient really rests, because the pain is usually adequately controlled by decreased activity.

There is some question as to whether there actually is a muscle relaxant; all drugs that are so designated probably act to some degree as tranquilizers. If one is required, however, methocarbamol and carisoprodol are most frequently used and can be employed intravenously as well as orally. The

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use of diazepam (Valium) for this purpose should be discouraged because it is actually a depressant and often adds to the patient’s psychologic problems.

Eighty percent of those who follow the foregoing regimen will be markedly improved, but it requires patience because frequently at least 6 weeks have passed before any additional therapy is indicated. Although the noninvasive treatment of a herniated disk can be quite gratifying, it generally requires a significant period of rest, and the patient must be aware of the time constraints from the beginning to understand the rationale behind the measures employed.

The long-term prognosis for patients with disk herniation is quite good. It has been shown that between 85% and 90% of surgically treated and nonsurgically treated patients were asymptomatic at 4 years. Less than 2% of both groups were symptomatic at 10 years.

Spinal Stenosis

Spinal stenosis can be defined as a narrowing of the spinal canal, and the mechanical pressure on the neural structures within depends upon the degree of narrowing. Every person’s spine, however, becomes narrower with age as a result of osteoarthritis. Not everyone with a narrowed spinal canal, however, has symptoms.

For those who do suffer, the discomfort can vary from mild annoyance to an inability to walk. The symptom complex is well documented. Patients of either sex, usually not before their fifth decade, first complain of vague pains, dysesthesias, and paresthesias with ambulation, but typically have excellent relief of their symptoms when they are sitting or lying supine. The increased lordotic stance assumed when walking, and particularly walking down grades, is most likely the inciting cause. The hyperextension further narrows the spinal canal and increases the symptoms.

With maturation of the syndrome, symptoms may even occur at rest. Muscle weakness, atrophy, and asymmetrical reflex changes may then appear; however, so long as the symptoms are only aggravated dynamically, neurologic changes occur only after the patient is stressed. The following stress tests can be used in an outpatient clinic: after a neurologic examination has been performed on the patient, he or she is asked to walk up and down the corridor until symptoms occur or the patient has walked 300 feet. A repeat examination is then done, and in many cases the second examination is positive for a focal neurologic deficit when the first was negative. Plain X-rays are often helpful in visualizing spinal stenosis, particularly degenerative spinal stenosis. One can see intervertebral disk degeneration, decreased interpedicular distance, a decreased sagittal canal diameter, and facet degeneration. If a patient fails conservative treatment and becomes a surgical candidate, the location and degree of neurologic compression can be assessed with MRI or a CT scan/myelogram.

The majority of patients with spinal stenosis, especially the degenerative and combined variety, can be treated nonsurgically with antiinflammatory medication.

Finally, a lumbosacral corset is often helpful in reminding the patient to avoid excessive motion. Symptoms are usually intermittent, and the individual often needs encouragement in getting through the episode without getting depressed. Nonoperative management is preferable so long as the pain is tolerable.

Spondylolisthesis

Spondylolisthesis is a spinal condition in which all or part of a vertebra has slipped forward on another. The word is derived from the Greek spondylos, meaning vertebra, and olisthesis, meaning to slip. There are several different types of spondylolisthesis, but the most common is that in which the lesion is in the isthmus or pars interarticularis. If a defect can be identified, but no slipping has occurred, the condition is termed spondylolysis; if one vertebra has slipped forward on another (horizontal translation), it is referred to as spondylolisthesis.

The etiology of the defect in spondylolysis is not clear. Although there may be a hereditary component, the lesion is seldom seen in patients under the age of 5 and is found in 5% of people over the age of 17. The most attractive explanation is that although these children inherit a potential deficiency in the pars, they are not born with any identifiable defect. Between the ages of 5 and 17 years, however, they become more active and a stress fracture, caused by repetitive hyperextension stresses, can develop into a spondylolysis. It is likely that most of these fractures occur during the period of rapid growth known as the adolescent growth spurt, and they are particularly prevalent in gymnasts and football players.

Spondylolisthesis has several characteristic features, but the forward displacement is easily recognized radiographically on the lateral projection (Figs. 7-10, 7-11). The degree of slip varies from patient to patient and can range from minimal displacement to complete dislocation of the vertebral body. Increased slipping rarely occurs after the age of 20 unless there has been a severe superimposed injury or surgical intervention. The period of most rapid progression coincides with the rapid growth spurt between the ages of 9 and 15.

The most common clinical manifestation of spondylolisthesis is low back pain. Although the cause of this type of back pain in the adult has been studied extensively, its origin is still not clear. There is no clear understanding of how so many patients develop this lesion between the ages of 5 and 17 but still have no back complaints until perhaps age 35, when a sudden twisting or lifting motion precipitates an acute episode of back and leg pain. Other patients with significant degrees of slipping, however, will go through life with no discomfort.

Although 50% of patients overall normally cannot associate an injury with the onset of the symptoms, of those working in industry almost all report an associated incident. It is possible to sustain an acute fracture of the pars, but it is a very rare occurrence. If the acuity of a pars defect is in question, it can be documented by a bone scan within 3 months of the injury; if the defect is long standing, the scan will be negative.

There is also frequently a buildup of a fibrocartilaginous mass at the defect, and this can cause pain by irritating the nerve root as it exits. It is thus not unusual that the patient with spondylolisthesis first complains of back pain but over time develops leg pain as the most annoying part of the problem.

Once the symptoms begin, the patient usually has constant low-grade back discomfort that is aggravated by activity and relieved by rest. There are some periods during which the pain is more intense than others, but unless the picture is complicated by severe leg pain, total incapacitation is rare. The patients are seldom aware of any sensory or motor deficit. At this point, it should be reemphasized that in some people even severe displacement is asymptomatic and gives rise to no disability. It is not uncommon to pick up a previously unrecognized spondylolisthesis on a routine gastrointestinal radiologic study of a 50-year-old patient.

The physical findings of this syndrome are fairly characteristic. In the absence of any radicular pain, the patient exhibits no postural scoliosis; but there is usually an exaggeration of the lumbar lordosis and a palpable “stepoff” with a dimple at the side of the abnormality. Occasionally, mild muscle spasm is demonstrable and, in most instances, some local tenderness can be elicited. Although the range of motion is usually complete, some pain can be expected on hyperextension.

Radiographs, particularly the lateral views, confirm the diagnosis. Even the slightest amount of forward slipping of the body of the involved vertebra is readily discernible, and the oblique views will disclose the actual defect in the pars.

The nonoperative treatment of the adult with spondylolisthesis is much the same as that used for backache from other causes. When the symptoms are acute, rest is indicated. If leg pain is a significant problem, then antiinflammatory medication can be quite beneficial. Exercises, usually a flexion–extension program, should be started once patients are in remission, and they are usually advised to own a corset for use during occasional strenuous activity. If conservative treatment is not successful, an operative approach can be considered that would include a spinal fusion.

Lumbar Spine Algorithm

As with patients with neck pain, the task of the physician when confronted with low back pain patients is to integrate their complaints into an accurate diagnosis and to prescribe appropriate therapy. This problem (universe of low back pain patients) has been formatted into an algorithm (Fig. 7-12),