Hyperguides

Orthopaedics / Spine

Lumbar Disk Herniations

Rahul Shah, MD Jonathan N. Grauer, MD Todd J. Albert, MD
Article

Introduction

Ninety-five percent of herniated disks are located in the lumbar spine.1 Lumbar herniated disks present as back pain or radicular leg pain or weakness (which is commonly referred to as sciatica). This pathologic condition was described as early as the 1930s by Mixter and Bar.2 Most people relate the discomfort associated with a herniated disk to an acute traumatic event, but there may be a history of intermittent back pain for many months, or even years, before the onset of leg pain. Overall, this degenerative process generally presents in healthy people in the third and fourth decades of life.3

Anatomy and Pathophysiology

Intervertebral disks are located between the vertebral bodies and are primarily composed of three biochemical components: collagen, proteoglycans, and water. Together, these components constitute 90% to 95% of the disk. However, this composition varies between the two anatomic regions; the outer annulus fibrosus is predominantly a ring of laminated collagen and the inner nucleus pulposus is gelatinous in nature (Slide 1).4

Slide 1

The nucleus, which is a remnant of the developmental notochord, is predominantly composed of type II collagen. Type II collagen, along with proteoglycans, helps maintain the hydration of the nucleus, allowing the nucleus to resist compression and act as a physiologic cushion. As an individual ages, proteoglycans diminish and the nucleus loses the ability to distribute axial loads.5

The annulus is composed of alternating laminae that are primarily composed of type I and type II collagen. The annulus is thinnest posterolaterally and thickest anteriorly. As the disk is loaded, the nucleus transfers axial loads to the annulus in the form of hoop stresses. With degenerative or traumatic processes, fissures or tears may develop in the annulus and the nucleus can herniate.6

A herniated nucleus pulposus (HNP) is a foreign material to the surrounding structures. The combination of mechanical pressure on a nerve root and local inflammation can lead to neurologic signs and symptoms.7 Following a disk herniation, the disk may undergo degenerative changes with fibrosis and narrowing and, eventually, spondylosis may develop.6

The direction of a disk herniation is important in its description. Posterolateral herniations are the most common. As noted above, this is when the annulus is the thinnest and, as such, where it is most vulnerable to allowing nuclear material to herniate. Posterolateral herniations are also the most clinically relevant type of herniation because the neural elements are posterior and posterolateral to the disk space (Slide 2). Disks can displace in other directions as well. Superior and inferior displacements into the vertebral body are known as Schmorl’s nodes. Anterior displacements are referred to as spondylosis deformans.8

Slide 2

A precise understanding of the nerve root anatomy is necessary to understand which nerve root will be affected by a disk herniation. In the lumbar spine, nerve roots exit the thecal sac, traverse approximately half a segment, and exit the spinal canal below the pedicle of their named vertebral body (Slide 3). A central posterior HNP leads to compression of the thecal sac and all of the traversing nerve roots. A posterolateral HNP can lead to compression of the traversing nerve, which is heading for the foramen of the subadjacent vertebral body (Slide 4). A far lateral HNP, which is less common, can lead to compression of the nerve root that has already exited the supra-adjacent foramen (Slide 4). In the example shown, a posterolateral L4-L5 HNP leads to L5 nerve root compression, while a far lateral L4-L5 HNP leads to L4 nerve root compression.

Slide 3 Slide 4

Disk herniations are described as protrusions, prolapses, extrusions, or sequestered herniations depending on how far the disk material displaces (Slide 5). A protrusion is a bulging of the nucleus through a weakened annulus. A prolapse is a rupture of the nucleus through the annulus but not through the posterior longitudinal ligament. An extrusion is a rupture of the nucleus through the annulus and the posterior longitudinal ligament. Finally, a sequestered herniation is a separation of a herniated fragment from the disk from which it came.9

Slide 5

Presentation and Evaluation

When evaluating a patient with back and/or leg pain, a detailed history should be obtained. Relevant information includes the chief complaint, location and nature of the symptoms (especially pain radiating to the extremity), character of pain, postural changes, effect of increased intrathecal pressure, and a complete review of symptoms (including psychiatric history). Acute injuries or precipitating events should be sought. Also, risk factors should be investigated such as repetitive lifting and prolonged sitting.

In addition to the above history, the physician should include fracture, tumor, and infection. Classically, tumor or infection can cause night pain without activities because the pelvic veins may become engorged upon reclining. Cauda equina syndrome must not be missed. Cauda equina presents with saddle anesthesia and bowel or bladder changes. A physician must also be aware of progressive neurologic deficits, as these may have irreversible sequelae.

A physical examination must next be performed. The patient should be observed for changes in posture or gait. A sciatic list may be noted away from a herniation pressing on the shoulder of a nerve root or toward a herniation pressing on the axilla of a nerve root. The spine should be palpated. Posterior spasm is consistent with pain; localizable tenderness raises concern for fracture, infection, or tumor. Range of motion should be measured. Flexion toward a herniation often exacerbates pain as a nerve root is pulled in its direction. Distal motor, reflex, and sensory examinations should also be performed. Nerve root specific tests are shown in Table 1.

Tension signs should be tested. A straight leg raise test or the bowstring sign can be performed with the patient in the supine or seated position. These maneuvers tension the roots contributing to the sciatic nerve, including L4-S1. Alternatively, a femoral stretch test can be performed in the standing or lateral position to test the L2-L4 nerve roots. A positive tension sign should be noted when radicular symptoms are reproduced. These are generally in the extremity being tested, however, contralateral symptoms may be produced with a massive or large axial herniation. Hip examination, FABER test (flexion, abduction, and external rotation), vascular evaluation (distal pulses), and abdominal and rectal examinations should also be performed to rule out other components of a patient’s presenting symptoms.

Radiographs are obtained for patients whose symptoms persist for more than 6 weeks of observation/treatment. Radiographs allow the clinician to rule out etiologies of pain such as masses, fractures, spondylolysis, and spondylolisthesis. Axial imaging such as computed tomography (CT) scans, CT myelograms, and magnetic resonance imaging (MRI) is indicated when other etiologies of back or leg pain must be excluded or when surgical intervention is being considered.

CT is noninvasive and shows bony stenosis and lateral pathologic conditions. When combined with an invasive component (myelography), neural compression can be better demonstrated. MRI is superior for identifying cord disorders, neural tumors, and far lateral disks. MRI is noninvasive, involves no ionizing radiation, and gives a myelogram-type picture with T2 imaging. MRI further allows evaluation of the hydration of the disks and visualization of the marrow of the vertebral bodies, allowing for screening of tumor and infection. Because of a high false-positive rate with MRI scans, correlation of findings with the history and physical examination is imperative.10

Treatment Options

The prognosis of HNP is generally good regardless of treatment. Patients operated on for proven disk herniations improved more rapidly than patients treated nonoperatively. However, within 4 to 5 years the outcomes begin to approximate each other.11

Treatment is based on the degree of pain and symptoms. Initial conservative treatments are aimed at reducing nerve root irritation. A period of rest is prescribed for 1 to 2 days with supports under the knees and neck to minimize root tension. Also, nonsteroidal anti-inflammatory drugs are used. Prolonged bed rest is no longer advocated because it can lead to deconditioning of compensatory musculature. Ambulation is begun as tolerated after the first few days of an acute event. More than one-half of patients who initially present with low back pain recover within 1 week and more than 90% of patients recover in 1 to 3 months.12 Physical therapy is started as tolerated.

If a patient fails to improve within 6 weeks of conservative care, a further work-up is warranted. In patients with predominant back pain, bone scan and medical work-up to rule out spinal tumors, infection, and nonspinal etiologies of pain are justified. If these studies are negative, back rehabilitation is continued. In patients who predominantly have leg pain and fail conservative modalities, a trial of epidural steroids or selective nerve root injections may be effective.

If a patient continues to fail conservative measures and has a clinical examination consistent with advanced imaging studies, surgical intervention should be considered. With proper indications, 95% of patients have initially good or excellent results, although up to 20% may have significant backache in long-term follow-up.13,14

The accepted procedure for a patient with a posterolateral HNP who has failed conservative treatment is a microdiskectomy (Slide 6). A midline incision is made and fascia is opened on the side of the pathology. Visualization is achieved with loupe magnification or a microscope. A hemilaminotomy is performed, the local ligamentum flavum is removed, the nerve root is retracted, and the offending disk fragment is removed. It is no longer believed that the entire disk has to be removed.15

Slide 6

Far lateral disks are difficult to access from the above noted approach without causing significant violation of the facets. Therefore, a far lateral HNP is generally approached with a Wiltze approach (Slide 7). The Wiltze approach accesses the intertransverse region via an intermuscular plane, the intertransverse membrane is taken down, and the offending disk fragment is removed extraforaminally. Clinical improvement is less predictable with this population when compared to that of patients with posterolateral disk herniations.16

Slide 7

Alternative surgical treatments have come in and out of favor including chymopapain, laser ablation, mechanical aspiration, and nucleotomes. None of these methods has been proven to be as consistent as microdiskectomy.

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