Degenerative Disorders of the Thoracic and Lumbar Spine

Neural elements

The organization of the neural elements is strictly maintained throughout the entire neural system, even within the conus medullaris and cauda equina distally. The orientation of the nerve roots in the dural sac and at the conus medullaris follows a highly organized pattern, with the most cephalad roots lying lateral and the most caudad lying centrally. The motor roots are ventral to the sensory roots at all levels. The arachnoid mater holds the roots in these positions.

The pedicle is the key to understanding surgical spinal anatomy. The relation of the pedicle to the neural elements varies by region within the spinal column. In the thoracic and lumbar spine, the named root exits below the named pedicle. Discs are formally named for the vertebral bodies between which they lie (e.g., the L4-5 disc is between the L4 and L5 vertebral bodies). This allows slightly more specificity in describing the discs if there is an anatomic variant (e.g., L4- S1) and less confusion than having the vertebral body, nerve root, and disc sharing the same name. Despite being less specific, the disc often is informally named for the vertebral level immediately cephalad (e.g., the L4 disc is immediately caudal to the L4 vertebra). In the lumbar spine, lateral recess pathology, such as lateral recess stenosis or posterolateral disc herniation, typically involves the next nerve root exiting caudal to that disc; for example, an L4-5 posterolateral disc herniation would be expected to cause L5 nerve root symptoms.

At the level of the intervertebral foramen is the dorsal root ganglion (DRG). The DRG lies within the outer confines of the foramen. Distal to the ganglion, three distinct branches arise; the most prominent and important is the ventral ramus, which supplies all structures ventral to the neural canal. The second branch, the sinuvertebral nerve, is a small filamentous nerve that originates from the ventral ramus and progresses medially over the posterior aspect of the disc and vertebral bodies, innervating these structures and the posterior longitudinal ligament. The third branch is the dorsal ramus. This branch courses dorsally, piercing the intertransverse ligament near the pars interarticularis. Three branches from the dorsal ramus innervate the structures dorsal to the neural canal. The lateral and intermediate branches provide innervation to the posterior musculature and skin. The medial branch separates into three branches to innervate the facet joint at that level and the adjacent levels above and below ( Fig. 39.1 ).

Disc innervation is through afferent axons with cell bodies within the DRG. Nociceptive signals are transmitted to the spinal cord by neurons from the DRG. Animal studies have revealed two paths between the annulus and the DRG: one from the sinuvertebral nerve and another along the paravertebral sympathetic trunk. The sinuvertebral nerve is a recurrent branch of the ventral ramus that connects back to the posterior disc at each level. The paired ganglia chains of the sympathetic trunks have axons that course through the gray rami communicantes to the spinal nerve. The disc is innervated by fibers from multiple levels. In animal models, the lateral annulus was found to be innervated by fibers coursing from the index level and two additional superior levels through the sinuvertebral nerves. Also, there was innervation through the sympathetic trunk by the DRG from the three levels even more superior than the sinuvertebral innervations. Contralateral DRG involvement also occurs through both pathways. Similar nonsegmental, multilevel innervation patterns also have been reported for the ventral disc surface. These complex multilevel innervations would help explain the pain patterns encountered clinically if similar patterns are present in humans. Also, innervations of the disc from the vertebral endplate have been shown. Intraosseous nerves follow the osseous vasculature. This endplate innervation is through a branch of the sinuvertebral nerve, the basivertebral nerve. This nerve enters the foramen, and the nerve fibers enter the vertebral margin with the vessels. The density of innervation is similar to that seen in the outer annulus, which suggests that the endplates are as important to pain generation as is the annulus.

Axial lumbar pain

Axial lumbar pain occurs at some point in the lives of most people. Appropriate treatment for what can be at times excruciating pain generally should begin with evaluation for a significant spinal pathologic process. This pathologic process being absent, a brief (1 to 3 days) period of bed rest with institution of an antiinflammatory regimen and rapid progression to an active exercise regimen with an anticipated return to full activity should be expected and encouraged. Generally, patients treated in this manner improve significantly in 4 to 8 weeks. Diagnostic studies, including radiographs, often are not helpful because they add little information. More sophisticated imaging with CT and MRI or other studies have even less utility initially. An overdependence on the diagnosis of disc herniation can occur with early use of these diagnostic studies, which show disc herniations in 20% to 36% of normal volunteers. General imaging guidelines have been developed to help identify patients for whom radiography is indicated ( Box 39.1 ).

Patients should understand that persistence of some pain does not indicate treatment failure, necessitating further measures; however, it is important for treating physicians to recognize that the longer a patient is limited by pain, the less likely he or she is to return to full activity.

For patients who do not respond to treatment regimens, early recognition that other issues may be involved is essential. Careful reassessment of complaints and reexamination for new information or findings and inconsistencies are necessary. Many studies of occupational back pain have revealed that depression, occupational mental stress, job satisfaction, intensity of concentration, anxiety, and marital status can be related to complaints of pain and disability. The role of these factors as causal or consequential of the symptoms remains an area of continued study; however, there is some evidence that the psychologic stresses occur before complaints of pain in some patients. Another finding that is evident from the literature is the inability of physicians to detect psychosocial factors adequately without using specific instruments designed for this purpose in patients with back pain. In one study, experienced spinal surgeons were able to identify distressed patients only 26% of the time based on patient interviews. Given the difficulty of identifying patients with psychosocial distress, being aware of the high incidence of incidental abnormal findings on imaging studies underscores the need for critical individual review of these studies by treating physicians. Severe nerve compression shown by MRI or CT correlates with symptoms of distal leg pain; however, mild-to-moderate nerve compression ( Table 39.1 ), disc degeneration or bulging, and central stenosis do not correlate significantly with specific pain patterns.

Radiography

The simplest and most readily available diagnostic tests for lumbar pain are anteroposterior and lateral radiographs of the involved spinal region. These simple radiographs show a relatively high incidence of abnormal findings; however, spinal radiographs on the initial visit for acute low back pain may not contribute to patient care and are not always cost effective. Plain radiographs may be considered only after the initial therapy fails, especially in patients younger than 45 years old.

There is insignificant correlation between back pain and the radiographic findings of lumbar lordosis, transitional vertebra, disc space narrowing, disc vacuum sign, and claw spurs. In addition, the entity of disc space narrowing is extremely difficult to quantify in all but operated backs or in obviously abnormal circumstances. A study of 321 patients found that only when traction spurs or obvious disc space narrowing or both were present did the incidence of severe back and leg pain, leg weakness, and numbness increase. These positive findings had no relationship to heavy lifting, vehicular exposure, or exposure to vibrating equipment. Other studies have shown some relationship between back pain and the findings of spondylolysis, spondylolisthesis, and adult scoliosis, but these findings also can be observed in spine radiographs of asymptomatic patients.

Special radiographic views can be helpful in further defining the initial clinical radiographic impression. Oblique views are useful in defining further spondylolisthesis and spondylolysis but are of limited use in facet syndrome and hypertrophic arthritis of the lumbar spine. Lateral flexion and extension radiographs may reveal segmental instability. The interpretation of these views depends on patient cooperation, patient positioning, and reproducible technique. Lateral lumbar flexion views are valid only if done in the seated position, which maximizes lumbar kyphosis. The Ferguson view (20-degree caudocephalic anteroposterior radiograph) has been shown to be of value in the diagnosis of the “far out syndrome,” that is, fifth root compression produced by a large transverse process of the fifth lumbar vertebra against the ala of the sacrum. Angled caudal views localized to areas of concern may show evidence of facet or laminar pathologic conditions.

Myelography

The value of myelography is the ability to check all spinal regions for abnormality and to define intraspinal lesions; it may be unnecessary if clinical and CT or MRI findings are in complete agreement. The primary indications for myelography are suspicion of an intraspinal lesion, patients with spinal instrumentation, or questionable diagnosis resulting from conflicting clinical findings and other studies. In addition, myelography is valuable in a previously operated spine and in patients with marked bony degenerative change that may be underestimated on MRI. Myelography is improved by the use of postmyelography CT in this setting and in evaluating spinal stenosis.

Several contrast agents have been used for myelography: air, oil contrast, and water-soluble (absorbable) contrast agents, including metrizamide (Amipaque), iohexol (Omnipaque), and iopamidol (Isovue-M). Because these nonionic agents are absorbable, the discomfort of removing them and the severity of the postmyelography headache have decreased.

Arachnoiditis is a severe complication that has been attributed occasionally to the combination of iophendylate and blood in the cerebrospinal fluid (CSF). This diagnosis usually is confirmed only by repeat myelography. Attempts at surgical neurolysis have resulted in only short-term relief and a return of symptoms within 6 to 12 months after the procedure. Time may decrease the effects of this serious problem in some patients, but progressive paralysis has been reported in rare instances. Arachnoiditis also can be caused by tuberculosis and other types of meningitis. Arachnoiditis has not been noted to be related to the use of a water-soluble contrast agent, with or without injection, in the presence of a bloody tap.

Water-soluble contrast media are now the standard agents for myelography. Their advantages include absorption by the body, enhanced definition of structures, tolerance, and the ability to vary the dosage for different contrasts. Similar to iophendylate, they are meningeal irritants, but they have not been associated with arachnoiditis. The complications of these agents include nausea, vomiting, confusion, and seizures. Rare complications include stroke, paralysis, and death. Iohexol and iopamidol have significantly lower complication rates than metrizamide. The more common complications seem to be related to patient hydration, phenothiazines, tricyclic antidepressants, and migration of contrast material into the cranial vault. Many reported complications can be prevented or minimized by using the lowest possible dose to achieve the desired degree of contrast. Adequate hydration and discontinuation of phenothiazines and tricyclic antidepressants before, during, and after the procedure also should minimize the incidence of the more common reactions. Likewise, maintenance of at least a 30-degree elevation of the patient’s head until the contrast material is absorbed should help prevent reactions. Complete information about these agents and the dosages required is found in their package inserts.

Iohexol is a nonionic contrast medium approved for thoracic and lumbar myelography. The incidence of reactions to this medium is low. The most common reactions are headache (<20%), pain (8%), nausea (6%), and vomiting (3%). Serious reactions are rare and include mental disturbances and aseptic meningitis (0.01%). Good hydration is essential to minimize the common reactions. The use of phenothiazine antinauseants is contraindicated when this medium is employed. Management before and after the procedure is the same as for metrizamide.

Air contrast is used rarely and probably should be used only in situations in which myelography is mandatory and the patient is extremely allergic to iodized materials. The resolution from such a procedure is poor. Air epidurography in conjunction with CT has been suggested in patients in whom further definition between postoperative scar and recurrent disc material is required.

Myelographic technique begins with a careful explanation of the procedure to the patient before its initiation. Hydration of the patient before the procedure may minimize postmyelographic complaints. Heavy sedation rarely is needed. Proper equipment, including a fluoroscopic unit with a spot film device, image intensification, tilt table, and television monitoring, is useful. The type of needle selected also influences the risk of postdural puncture headaches, which can be severe. Smaller gauge needles (22- or 25-gauge) have been found to result in a lower incidence of postdural puncture headaches. Also, use of a Whitacre-type needle with a blunter tip and side port opening results in fewer postdural puncture headache complaints.

The most common technical complications of myelography are significant retention of contrast medium (oil contrast only), persistent headache from a dural leak, and epidural injection. These problems usually are minor. Persistent dural leaks usually are responsive to a blood patch. With the use of a water-soluble contrast medium, the persistent abnormalities caused by retained medium and epidural injection are eliminated.

Computed tomography

CT can be a useful diagnostic tool in the evaluation of spinal disease ( Fig. 39.2 ). The current technology and computer software have made possible the ability to reformat the standard axial cuts in almost any direction and magnify the images so that exact measurements of various structures can be made. Software is available to evaluate the density of a selected vertebra and compare it with vertebrae of the normal population to give a numerically reproducible estimate of vertebral density to quantitate osteopenia.

Numerous types of CT studies for the spine are available. One must be careful when ordering the study to ensure that the areas of clinical concern are included. The most common routine for lumbar disc herniations consists of making serial cuts through the last three lumbar intervertebral discs. If the equipment has a tilting gantry, an attempt is made to keep the axis of the cuts parallel with the discs. Frequently, the gantry cannot tilt enough, however, to allow a parallel beam through the lowest disc space. This technique does not allow demonstration of the canal at the pedicles. Another method involves making cuts through the discs without tilting the gantry. The entire canal is not shown, and the lower cuts frequently have the lower and upper endplates of adjacent vertebrae superimposed in the same view.

The most complex method consists of making multiple parallel cuts at equal intervals. This allows computer reconstruction of the images in different planes, usually sagittal and coronal. These reformatted views allow an almost three-dimensional view of the spine and most of its structures. The greatest benefit of this technique is the ability to see beyond the limits of the dural sac and root sleeves. The diagnosis of foraminal encroachment by bone or disc material can be made in the face of a normal myelogram. The proper procedure can be chosen that fits all of the pathologic conditions involved.

Optimal reformatted CT should include enlarged axial and sagittal views with clear notation as to laterality and sequence of cuts. Several sections of the axial cuts should include the local soft tissue and contiguous abdominal contents. Finally, a set of images adjusted for improved bony detail should be included for evaluation of the facet joints and the lateral recesses. This study should be centered on the level of greatest clinical concern. The study can be enhanced further if done after water contrast myelography or with intravenous injection of a contrast medium. Enhancement techniques are especially useful if the spine being evaluated has been operated on previously.

This noninvasive, painless outpatient procedure can supply more information about spinal disease than was previously available with a battery of invasive and noninvasive tests usually requiring hospitalization. CT does not show intraspinal tumors or arachnoiditis and is unable to differentiate scar from recurrent disc herniation. The use of intravenous contrast medium ( Fig. 39.2F ) followed by CT can improve the definition between scar and disc herniation. Myelography is still required to show intraspinal tumors and to “run” the spine to detect occult or unsuspected lesions. The development of low-dose metrizamide or iohexol myelography with reformatted CT done as an outpatient procedure allows maximal information to be obtained with minimal time, risk, discomfort, and cost.

Magnetic resonance imaging

MRI is currently the standard for advanced imaging of the spine and is superior to CT in most circumstances, in particular identification of infections, tumors, and degenerative changes within the discs ( Fig. 39.3 ). More important, MRI is superior for imaging the disc and directly images neural structures. Also, MRI typically shows the entire region of study (cervical, thoracic, or lumbar). Of particular value is the ability to image the nerve root in the foramen, which is difficult even with postmyelography CT because the subarachnoid space and the contrast agent do not extend fully through the foramen. Despite this superiority, there are circumstances in which MRI and CT, with or without myelography, can be used in a complementary fashion.

One of the difficulties with MRI is showing anatomy that is abnormal but may be asymptomatic. MRI evidence of disc degeneration has been reported in the cervical spine in 25% of patients younger than 40 years and in 60% of patients 60 years and older, and lumbar disc degeneration was found in 35% of patients 20 to 39 years old and in 100% of patients older than 50. The demonstrated findings must be carefully correlated with the clinical impression. The importance of this concept cannot be overstated. The best way to obtain meaningful clinical information from MRI of the spine is to have a specific question before the study. This question is derived from the patient’s history and careful physical examination and is posed using the parameters of (1) neural compression, (2) instability, and (3) deformity. In each case the specific location of the abnormality should be suspected before MRI and confirmed with the study. Only abnormalities in one or a combination of these categories are important, and operative techniques can treat only these problems. Failure to interpret an imaging study in this way, especially MRI, which is sensitive to anatomic abnormalities, would inevitably lead to poor clinical choices and outcomes.

Other diagnostic tests

Numerous diagnostic tests have been used in the diagnosis of intervertebral disc disease in addition to radiography, myelography, CT, and MRI. The primary advantage of these tests is to rule out diseases other than primary disc herniation, spinal stenosis, and spinal arthritis.

Electromyography is the most notable of these tests. One advantage of electromyography is in the identification of peripheral neuropathy and diffuse neurologic involvement indicating higher or lower lesions. Electromyography and nerve conduction velocity can be helpful if a patient has a history and physical examination suggestive of radiculopathy at either the cervical or lumbar level with inconclusive imaging studies. Paraspinal muscles in a patient with a previous posterior operation usually are abnormal and are not a reliable diagnostic finding.

Bone scans are another procedure in which positive findings usually are not indicative of intervertebral disc disease, but they can confirm neoplastic, traumatic, and arthritic problems in the spine. Various laboratory tests, such as a complete blood cell count, differential white blood cell count, C-reactive protein, biochemical profile, urinalysis, serum protein electrophoresis, and erythrocyte sedimentation rate, are extremely good screening procedures for other causes of pain in the spine. Rheumatoid screening studies, such as those for rheumatoid arthritis, antinuclear antibody, lupus erythematosus cell preparation, and HLA-B27, also are useful when indicated by the clinical picture.

Some tests that were developed to enhance the diagnosis of intervertebral disc disease have been surpassed by more advanced technology. Lumbar venography and ultrasonographic measurement of the intervertebral canal are two examples.

Injection studies

Whenever a diagnosis is in doubt and the complaints seem real or the pathologic condition is diffuse, identification of the source of pain is problematic. The use of local anesthetics or contrast media in various specific anatomic areas can be helpful. These agents are relatively simple, safe, and minimally painful. Contrast media such as diatrizoate meglumine (Hypaque), iothalamate meglumine (Conray), iohexol (Omnipaque), iopamidol, and metrizamide (Amipaque) have been used for discography and blocks with no reported ill effects. Reports of neurologic complications with contrast media used for discography and subsequent chymopapain injection are well documented. The best choice of a contrast medium for documenting structures outside the subarachnoid space is an absorbable medium with low reactivity, because it might be injected inadvertently into the subarachnoid space. Iohexol and metrizamide are the least reactive, most widely accepted, and best tolerated of the currently available contrast media. Local anesthetics, such as lidocaine (Xylocaine), tetracaine (Pontocaine), and bupivacaine (Marcaine), are used frequently epidurally and intradurally. The use of bupivacaine should be limited to low concentrations and low volumes because of reports of death after epidural anesthesia using concentrations of 0.75% or higher.

Steroids prepared for intramuscular injection also have been used frequently in the epidural space with few and usually transient complications. Spinal arachnoiditis in past years was associated with the use of epidural methylprednisolone acetate (Depo-Medrol). This complication was thought to be caused by the use of the suspending agent, polyethylene glycol, which has since been eliminated from the Depo-Medrol preparation. For epidural injections, we prefer the use of Celestone Soluspan, which is a mixture of betamethasone sodium phosphate and betamethasone acetate. Celestone Soluspan provides immediate and long-term duration of action, is highly soluble, and contains no harmful preservatives. Celestone should not be mixed with local anesthetics containing preservatives such as parabens or phenol because flocculation and clogging of the suspension can occur. If Celestone is not available, other commonly used preparations for spinal injections include methylprednisolone (Depo-Medrol) and triamcinolone acetonide (Kenalog). Isotonic saline is the only other injectable medium used frequently around the spine with no reported adverse reactions. All substrates injected into the epidural space should be preservative free.

Steroids and local anesthesia are generally used in combination for antiinflammatory and analgesic effects. It is theorized that the lipophilic characteristic of the steroid permits sustained release from the abundant epidural fat, which is where the steroid is injected. Cells exposed to the steroid synthesize a phospholipase A2-inhibitory glycoprotein (termed lipomodulin) and inhibit the inflammatory pathway. Phospholipase A2, which is an inflammatory enzyme, converts membrane phospholipids into arachidonic acid and subsequently controls lipoxygenase, leading to the formation of leukotrienes. The steroid also reduces nerve swelling and upregulates the transcription of antiinflammatory genes, in contrast to local analgesics, which are responsible for immediate pain relief.

When discrete, well-controlled injection techniques directed at specific targets in and around the spine are used, grading the degree of pain before and after a spinal injection is helpful in determining the location of the pain generator. The patient is asked to grade the degree of pain on a 0-to-10 scale before and at various intervals after the spinal injection (see Box 38.1 ). If a spinal injection done under fluoroscopic control results in an 80% or more decrease in the level of pain, which corresponds to the duration of action of the anesthetic agent used, we presume the target area injected to be the pain generator. Less pain reduction, 50% to 65%, does not constitute a positive response.

Signs and symptoms

The natural history of symptomatic thoracic disc disease is similar to that in other areas, in that symptoms and function typically improve with conservative treatment and time. The clinical course can vary, however, and a high index of suspicion must be maintained to make the correct diagnosis. The differential diagnosis for the symptoms of thoracic disc herniations is fairly extensive and includes nonspinal causes occurring with the cardiopulmonary, gastrointestinal, and musculoskeletal systems. Spinal causes of similar symptoms can occur with infectious, neoplastic, degenerative, and metabolic problems within the spinal column and the spinal cord.

Two general patient populations have been documented in the literature. The smaller group of patients is younger and has a relatively short history of symptoms, often with a history of trauma. Typically, an acute soft disc herniation with either acute spinal cord compression or radiculopathy is present. Outcome generally is favorable with operative or nonoperative treatment. The larger group of patients has a longer history, often more than 6 to 12 months of symptoms, which result from chronic spinal cord or root compression. Disc degeneration, often with calcification of the disc, is the underlying process.

Pain is the most common presenting feature of thoracic disc herniations. Two patterns of pain are apparent: one is axial, and the other is bandlike radicular pain along the course of the intercostal nerve. The T10 dermatomal level is the most commonly reported distribution, regardless of the level of involvement. This is a band extending around the lower lateral thorax and caudad to the level of the umbilicus. This radicular pattern is more common with upper thoracic and lateral disc herniations. Some axial pain often occurs with this pattern as well. Associated sensory changes of paresthesias and dysesthesia in a dermatomal distribution also occur ( Fig. 39.19 ). High thoracic discs (T2 to T5) can manifest similarly to cervical disc disease with upper arm pain, paresthesias, radiculopathy, and Horner syndrome. Myelopathy also may occur. Complaints of weakness, which may be generalized by the patient, typically involving both lower extremities occur in the form of mild paraparesis. Sustained clonus, a positive Babinski sign, and wide-based and spastic gait all are signs of myelopathy. Bowel and bladder dysfunction occur in only 15% to 20% of these patients. The neurologic evaluation of patients with thoracic disc herniations must be meticulous because there are few localizing findings. Abdominal reflexes, cremasteric reflex, dermatomal sensory evaluation, rectus abdominis contraction symmetry, lower extremity reflexes and strength and sensory examinations, and determination of long tract findings all are important.

Confirmatory imaging

Plain radiographs are helpful to evaluate traumatic injuries and to determine potential osseous morphologic variations that may help to localize findings, especially on intraoperative films, if these become necessary. MRI is the most important and useful imaging method to show thoracic disc herniations. In addition to the disc herniation, neoplastic or infectious pathology can be seen. The presence of intradural pathology, including disc fragments, also usually is shown on MRI. The spinal cord signal may indicate the presence of inflammation or myelomalacia as well. Despite all of these advantages, MRI may underestimate the thoracic disc herniation, which often is calcified and has low signal intensity on T1- and T2-weighted sequences.

Myelography followed by CT also can be useful in evaluating the bony anatomy and more accurately assessing the calcified portion of the herniated thoracic disc. Regardless of the imaging methods used, the appearance and presence of a thoracic disc herniation must be carefully considered and correlated with the patient’s complaints and detailed examination findings. Relief of pain with thoracic transforaminal epidural can confirm the source of pain and is a good predictor of improvement with surgical intervention.

Treatment results

As mentioned previously, nonoperative treatment usually is effective. A specific regimen cannot be recommended for all patients; however, the principles of short-term rest, pain relief, antiinflammatory agents, and progressive directed activity restoration seem most appropriate. These measures generally should be continued at least 6 to 12 weeks if feasible. If neurologic deficits progress or manifest as myelopathy, or if pain remains at an intolerable level, surgery should be recommended. The initial procedure recommended for this lesion was posterior thoracic laminectomy and disc excision. At least half of the lesions have been identified as being central, making the excision from this approach extremely difficult, and the results were disheartening. Most series reported fewer than half of the patients improving, with some becoming worse after posterior laminectomy and discectomy. Recent studies suggest that lateral rachiotomy (modified costotransversectomy) or an anterior transthoracic approach for discectomy produces considerably better results with no evidence of worsening after the procedure.

Video-assisted thoracic surgery (VATS) has been used in several series to remove central thoracic disc herniations successfully without the need for a thoracotomy or fusion.

The most promising and least invasive technique for surgical treatment of thoracic disc herniation is awake transforaminal endoscopic discectomy. It can be used to treat thoracic herniations of the midline without the morbidity of chest surgery, fusion, or even general anesthesia.

Operative treatment

The best operative approach for these lesions depends on the specific characteristics of the disc herniation and on the particular experience of the surgeon. Simple laminectomy has no role in the treatment of thoracic disc herniations. Posterior approaches, including costotransversectomy, transpedicular, transfacet pedicle-sparing, transdural, and lateral extracavitary approaches, all have been used successfully. Anterior approaches via thoracotomy, a transsternal approach, retropleural approach, or VATS also have been used successfully ( Fig. 39.20 ). More recently, a number of minimally invasive posterior and anterior techniques have been developed, most using a series of muscle dilators, tubular retractors, and microscope visualization. The surgical intervention with the least morbidity is awake transforaminal endoscopic discectomy when used for herniations accessible by that approach.

Signs and symptoms

Although back pain is common from the second decade of life on, intervertebral disc disease and disc herniation are most prominent in otherwise healthy people in the third and fourth decades of life. Most people relate their back and leg pain to a traumatic incident, but close questioning frequently reveals that the patient has had intermittent episodes of back pain for many months or even years before the onset of severe leg pain. In many instances, the back pain is relatively fleeting and is relieved by rest. Heavy exertion, repetitive bending, twisting, or heavy lifting often brings on axial back pain. In other instances, an inciting event cannot be elicited. The pain usually begins in the lower back, radiating to the sacroiliac region and buttocks. The pain can radiate down the posterior thigh. Back and posterior thigh pain of this type can be elicited from many areas of the spine, including the facet joints, longitudinal ligaments, and periosteum of the vertebra. Radicular pain usually extends below the knee and follows the dermatome of the involved nerve root ( Fig. 39.22 ).

The usual history of lumbar disc herniation is of repetitive lower back and buttock pain, relieved by a short period of rest. This pain is suddenly exacerbated, often by a flexion episode, with the appearance of leg pain. Most radicular pain from nerve root compression caused by a herniated nucleus pulposus is evidenced by leg pain equal to, or in many cases greater than, the degree of back pain. Whenever leg pain is minimal and back pain is predominant, great care should be taken before making the diagnosis of a symptomatic herniated intervertebral disc. The pain from disc herniation usually varies, increasing with activity, especially sitting and driving.

The pain can be decreased by rest, especially in the semi-Fowler position, and can be exacerbated by straining, sneezing, or coughing. Whenever the pattern of pain is bizarre or the pain is uniform in intensity, a diagnosis of symptomatic herniated disc should be viewed with some skepticism.

Other symptoms of disc herniation include weakness and paresthesias. In most patients, the weakness is intermittent, varies with activity, and is localized to the neurologic level of involvement. Paresthesias also vary and are limited to the dermatome of the involved nerve root. Whenever these complaints are generalized, the diagnosis of a simple unilateral disc herniation should be questioned.

Numbness and weakness in the involved leg and occasionally pain in the groin or testis can be associated with a high or midline lumbar disc herniation. If a fragment is large or the herniation is high, symptoms of pressure on the entire cauda equina can occur with development of cauda equina syndrome. These symptoms include numbness and weakness in both legs, rectal pain, numbness in the perineum, and paralysis of the sphincters. This diagnosis should be the primary consideration in patients who complain of sudden loss of bowel or bladder control. Whenever the diagnosis of cauda equina syndrome is caused by an acute midline herniation, evaluation and treatment should be aggressive.

The physical findings with disc disease vary because of the time intervals involved. Usually patients with acute pain show evidence of marked paraspinal spasm that is sustained during walking or motion. A scoliosis or a list in the lumbar spine may be present, and in many patients the normal lumbar lordosis is lost. As the acute episode subsides, the degree of spasm diminishes remarkably, and the loss of normal lumbar lordosis may be the only telltale sign. Point tenderness may be present over the spinous process at the level of the disc involved, and pain may extend laterally in some patients.

If there is nerve root irritation, it centers over the length of the sciatic nerve, in the sciatic notch, and more distally in the popliteal space. In addition, stretch of the sciatic nerve at the knee should reproduce buttock, thigh, and leg pain (i.e., pain distal to the knee). A Lasègue sign usually is positive on the involved side. A positive Lasègue sign or straight-leg raising should elicit buttock and leg pain distal to the knee. Occasionally, if leg pain is significant, the patient leans back from an upright sitting position and assumes the tripod position to relieve the pain. This is referred to as the “flip sign.” Contralateral leg pain produced by straight-leg raising should be regarded as pathognomonic of a herniated intervertebral disc. The absence of a positive Lasègue sign should make one skeptical of the diagnosis, although older individuals may not have a positive Lasègue sign and tend toward more claudicatory symptoms. Likewise, inappropriate findings and inconsistencies in the examination usually are nonorganic in origin (see discussion of nonspecific axial pain). If the leg pain has persisted for any length of time, atrophy of the involved limb may be present, as shown by asymmetric girth of the thigh or calf. The neurologic examination varies as determined by the level of root involvement ( Boxes 39.2 to 39.4 ).

Unilateral disc herniation at L3-4 usually compresses the L4 root as it crosses the disc before exiting at the L4-5 intervertebral foramen below the L4 pedicle. Pain may be localized around the medial side of the leg. Numbness may be present over the anteromedial aspect of the leg. The anterior tibial muscle may be weak, as evidenced by inability to heel walk. The quadriceps and hip adductor group, both innervated from L2, L3, and L4, also may be weak and, in extended ruptures, atrophic. Reflex testing may reveal a diminished or absent patellar tendon reflex (L2, L3, and L4) or anterior tibial tendon reflex (L4). Sensory testing may show diminished sensibility over the L4 dermatome, the isolated portion of which is the medial leg (see Fig. 39.22 ) and the autonomous zone of which is at the level of the medial malleolus.

Unilateral disc herniation at L4-5 results in compression of the L5 root. L5 root radiculopathy should produce pain in the dermatomal pattern. Numbness, when present, follows the L5 dermatome along the anterolateral aspect of the leg and the dorsum of the foot, including the great toe. The autonomous zone for this nerve is the dorsal first web of the foot and the dorsum of the third toe. Weakness may involve the extensor hallucis longus (L5), gluteus medius (L5), or extensor digitorum longus and brevis (L5). Reflex change usually is not found. A diminished posterior tibial reflex is possible but difficult to elicit.

With unilateral rupture of the disc at L5-S1, the findings of an S1 radiculopathy are noted. Pain and numbness involve the dermatome of S1. The S1 dermatome includes the lateral malleolus and the lateral and plantar surface of the foot, occasionally including the heel. There is numbness over the lateral aspect of the leg and, more important, over the lateral aspect of the foot, including the lateral three toes. The autonomous zone for this root is the dorsum of the fifth toe. Weakness may be shown in the peroneus longus and brevis (S1), gastrocnemius-soleus (S1), or gluteus maximus (S1). In general, weakness is not a usual finding in S1 radiculopathy. Occasionally, mild weakness may be shown by asymmetric fatigue with exercise of these motor groups. The ankle jerk usually is reduced or absent.

Massive extrusion of a disc involving the entire diameter of the lumbar canal or a large midline extrusion can produce pain in the back, legs, and occasionally perineum. Both legs may be paralyzed, the sphincters may be incontinent, and the ankle jerks may be absent.

More than 95% of the ruptures of the lumbar intervertebral discs occur at L4-5 or L5-S1. Ruptures at higher levels in many patients are not associated with a positive straight-leg raising test. In these instances, a positive femoral stretch test can be helpful. This test is done by placing the patient prone and acutely flexing the knee while placing the hand in the popliteal fossa. When this procedure results in anterior thigh pain, the result is positive and a high lesion should be suspected. In addition, these lesions may occur with a more diffuse neurologic complaint without significant localizing neurologic signs.

Often the neurologic signs associated with disc disease vary over time. If the patient has been up and walking for a period of time, the neurologic findings may be much more pronounced than if he or she has been at bed rest for several days, decreasing the pressure on the nerve root and allowing the nerve to resume its normal function. In addition, various conservative treatments can change the physical signs of disc disease.

Comparative bilateral examination of a patient with back and leg pain is essential in finding a clear-cut pattern of signs and symptoms. The evaluation commonly may change. Adverse changes in the examination may warrant more aggressive therapy, whereas improvement of the symptoms or signs should signal a resolution of the problem. Early symptoms or signs suggesting cauda equina syndrome or severe or progressive neurologic deficit should be treated aggressively from the onset.

Differential diagnosis

The differential diagnosis of back and leg pain is extremely lengthy and complex. It includes diseases intrinsic to the spine and diseases involving adjacent organs but causing pain referred to the back or leg. For simplicity, lesions can be categorized as being extrinsic or intrinsic to the spine. Extrinsic lesions include diseases of the urogenital system, gastrointestinal system, vascular system, endocrine system, nervous system not localized to the spine, and extrinsic musculoskeletal system. These lesions include infections, tumors, metabolic disturbances, congenital abnormalities, and associated diseases of aging. Intrinsic lesions involve diseases that arise primarily in the spine. They include diseases of the spinal musculoskeletal system, the local hematopoietic system, and the local neurologic system. These conditions include trauma, tumors, infections, diseases of aging, and immune diseases affecting the spine or spinal nerves.

Although the predominant cause of back and leg pain in healthy individuals usually is lumbar disc disease, one must be extremely cautious to avoid a misdiagnosis, particularly given the high incidence of disc herniations present in asymptomatic patients as discussed previously. A full physical examination must be completed before making a presumptive diagnosis of herniated disc disease. Common diseases that can mimic disc disease include ankylosing spondylitis, multiple myeloma, vascular insufficiency, arthritis of the hip, osteoporosis with stress fractures, extradural tumors, peripheral neuropathy, and herpes zoster. Infrequent but reported causes of sciatica not related to disc herniation include synovial cysts, rupture of the medial head of the gastrocnemius, sacroiliac joint dysfunction, lesions in the sacrum and pelvis, and fracture of the ischial tuberosity.

Confirmatory imaging

Although the diagnosis of a herniated lumbar disc should be suspected from the history and physical examination, imaging studies are necessary to rule out other causes, such as a tumor or infection. Plain radiographs are of limited use in the diagnosis because they do not show disc herniations or other intraspinal lesions, but they can show infection, tumors, or other anomalies and should be obtained, especially if surgery is planned. Currently, the most useful test for diagnosing a herniated lumbar disc is MRI ( Figs. 39.23 and 39.24 ). Since the advent of MRI, myelography is used much less frequently, although in some situations it may help to show subtle lesions. When myelography is used, it should be followed by CT.

Nonoperative treatment

The number and variety of nonoperative therapies for back and leg pain are diverse and overwhelming. Treatments range from simple rest to expensive traction apparatus. All of these therapies are reported with glowing accounts of miraculous “cures”; few have been evaluated scientifically. In addition, the natural history of lumbar disc herniation is characterized by exacerbations and remissions with eventual improvement of extremity complaints in most cases, which can make any intervention appear successful to the patient. Finally, several distinct symptom complexes seem to be associated with disc disease. Few, if any, studies have isolated the response to specific and anatomically distinct diagnoses.

The simplest treatment for acute back pain is rest; generally 2 days of bed rest are better than a longer period. Biomechanical studies indicate that lying in a semi-Fowler position (i.e., on the side with the hips and knees flexed) with a pillow between the legs should relieve most pressure on the disc and nerve roots. Muscle spasm can be controlled by the application of ice, preferably with a massage over the muscles in spasm. Pain relief and antiinflammatory effect can be achieved with NSAIDs. Most acute exacerbations of back pain respond quickly to this therapy. As the pain diminishes, the patient should be encouraged to begin isometric abdominal and lower extremity exercises. Walking within the limits of comfort also is encouraged. Sitting, especially riding in a car, is discouraged. Continuation of ordinary activities within the limits permitted by pain has been shown to lead to a quicker recovery.

Education in proper posture and body mechanics is helpful in returning the patient to the usual level of activity after the acute exacerbation has improved. This education can take many forms, from individual instruction to group instruction. Back education of this type is now usually referred to as “back school.” Although the concept is excellent, the quality and quantity of information provided may vary widely. The work of Bergquist-Ullman and Larsson and others indicates that patient education of this type is extremely beneficial in decreasing the amount of time lost from work initially but does little to decrease the incidence of recurrence of symptoms or length of time lost from work during recurrences. The combination of back education and combined physical therapy is superior to placebo treatment. Physical therapy can help improve activity level and physical function but should be discontinued if it aggravates the radiculopathy.

Numerous medications have been used with various results in subacute and chronic back and leg pain syndromes. The current trend seems to be moving away from the use of strong narcotics and muscle relaxants in the outpatient treatment of these syndromes. This is especially true in the instances of chronic back and leg pain where drug habituation and increased depression are frequent. Oral steroids used briefly can be beneficial as potent antiinflammatory agents. The many types of NSAIDs also are helpful when aspirin is not tolerated or is of little help. Numerous NSAIDs are available for the treatment of low back pain. When depression is prominent, mood elevators such as nortriptyline can be beneficial in reducing sleep disturbance and anxiety without increasing depression. Nortriptyline also decreases the need for narcotic medication.

Physical therapy should be used judiciously. The exercises should be fitted to the symptoms and not forced as an absolute group of activities. Patients with acute back and thigh pain eased by passive extension of the spine in the prone position can benefit from extension exercises rather than flexion exercises. Improvement in symptoms with extension indicates a good prognosis with conservative care. Patients whose pain is increased by passive extension may be improved by flexion exercises. These exercises should not be forced in the face of increased pain. This may avoid further disc extrusion. Any exercise that increases pain should be discontinued. Lower extremity exercises can increase strength and relieve stress on the back, but they also can exacerbate lower extremity arthritis. The true benefit of such treatments may be in the promotion of good posture and body mechanics rather than of strength. Numerous treatment methods have been advanced for the treatment of back pain. Some patients respond to the use of transcutaneous electrical nerve stimulation. Others do well with traction varying from skin traction in bed with 5 to 8 lb to body inversion with forces of more than 100 lb. Back braces or corsets may be helpful to other patients. Ultrasound and diathermy are other treatments used in acute back pain. The scientific efficacy of many of these treatments has not been proved.

As discussed earlier, the natural history of lumbar disc disease generally is favorable. Although low-back pain can result in significant disability, approximately 95% of patients return to their previous employment within 3 months of symptom onset. Failure to return to work within 3 months has been identified as a poor prognostic sign. Longer periods of disability equate to lower probability of returning to work: in patients with total disability lasting a year, the likelihood of returning to work is 21%, and in those with disability lasting 2 years the likelihood is less than 2%. Obesity and smoking have been shown to correlate unfavorably with low back pain and may adversely affect the progression of symptoms.

Operative treatment

If nonoperative treatment for lumbar disc disease fails, the next consideration is operative treatment. Before this step is taken, the surgeon must be sure of the diagnosis. The patient must be certain that the degree of pain and impairment warrants such a step. The surgeon and the patient must realize that disc surgery is not a cure but may provide symptomatic relief. It neither stops the pathologic processes that allowed the herniation to occur nor restores the disc to a normal state. The patient still must practice good posture and body mechanics after surgery. Activities involving repetitive bending, twisting, and lifting with the spine in flexion may have to be curtailed or eliminated. If prolonged relief is to be expected, some permanent modification in the patient’s lifestyle may be necessary, although often no specific limitations are applied.

The key to good results in disc surgery is appropriate patient selection. The optimal patient is one with predominant (if not only) unilateral leg pain extending below the knee that has been present for at least 6 weeks. The pain should have been decreased by rest, antiinflammatory medication, or even epidural steroids but should have returned to the initial levels after a minimum of 6 to 8 weeks of conservative care. Physical examination should reveal signs of sciatic irritation and possibly objective evidence of localizing neurologic impairment. CT, lumbar MRI, or myelography should confirm the level of involvement consistent with the patient’s examination.

Operative disc removal is mandatory and urgent only in patients with cauda equina syndrome; other disc excisions should be considered elective. The elective status of surgery should allow a thorough evaluation to confirm the diagnosis, level of involvement, and physical and psychologic status of the patient. Frequently, if there is a rush to the operating room to relieve pain without proper investigation, the patient and the physician later regret the decision.

Regardless of the method chosen to treat a disc rupture surgically, the patient should be aware that the procedure is predominantly for the symptomatic relief of leg pain. Patients with predominantly back pain may not experience relief.

Microdiscectomy

Most disc surgery is performed with the patient under general endotracheal anesthesia, although local anesthesia has been used with minimal complications. Patient positioning varies with the operative technique and surgeon. To position the patient in a modified kneeling position, a specialized frame or custom frame is popular. Positioning the patient in this manner allows the abdomen to hang free, minimizing epidural venous dilation and bleeding ( Fig. 39.25 ). A headlamp allows the surgeon to direct light into the lateral recesses where a large proportion of the surgery may be required. The addition of loupe magnification also greatly improves the identification and exposure of various structures. Most surgeons also use an operative microscope to improve visibility further. The primary benefit of an operating microscope compared with loupes is the narrowed interocular distance while maintaining binocular vision and the view afforded the assistant. Radiographic confirmation of the proper level is necessary. Care should be taken to protect neural structures. Epidural bleeding should be controlled with bipolar electrocautery. Any sponge, pack, or cottonoid patty placed in the wound should extend to the outside. Pituitary rongeurs should be marked at a point equal to the maximal allowable disc depth to prevent injury of viscera or great vessels.

Microscopic Lumbar Disc Excision

Microscopic lumbar disc excision has replaced the standard open laminectomy as the procedure of choice for herniated lumbar disc. This procedure can be done on an outpatient basis and allows better lighting, magnification, and angle of view with a much smaller exposure. Because of the limited dissection required, there is less postoperative pain and a shorter postoperative stay.

Microscopic lumbar discectomy requires an operating microscope with a 400-mm lens, a variety of small-angled Kerrison rongeurs of appropriate length, microinstruments, and preferably a combination suction/nerve root retractor. The procedure is performed with the patient prone. A specialized frame (see Fig. 39.25 ) previously described can be used, or the patient can be positioned on chest rolls. There are several advantages to using a specialized table, such as an Andrews table: (1) it allows the belly to hang free where venous blood will pool, which results in decreased venous epidural bleeding intraoperatively; (2) the knee-chest position maximizes the lumbar kyphosis, placing the ligamentum flavum on slight tension that allows for easier removal but also opens the interlaminar space, which may provide greater canal access with less bone removal; and (3) the small footprint of the bed enables the operating microscope to be placed at the foot, which not only makes access to the ocular lens easier for both the surgeon and assistant standing on opposite sides of the table but also allows the fluoroscope to be moved into the surgical field for imaging without having to move the microscope base itself.

The microscope can be used from skin incision to closure. The initial dissection can be done under direct vision, however. A lateral radiograph is taken to confirm the level, but fluoroscopy is much quicker when used for localization. Fluoroscopy is essential for localization when using tubular retractors because the field of view is smaller, making the available margin for error in placing the skin incision less.

Tubular Techniques

Tubular techniques have been developed with the purported advantage of shortened hospital stay, faster return to activity, and fewer wound issues. These techniques generally are variations of the microdiscectomy technique using a tubular retractor rather than the McCulloch and different types of bayoneted instruments. This remains another alternative technique. The basic principles remain the same as with microdiscectomy. The less-invasive tubular retractors have been used in a transmuscular fashion, allowing disc excision with less soft-tissue damage because of the more precise exposure; however, better objective clinical results have not been shown with this technique.