Degenerative Disk Disease

Background

The prevalence of low back and neck pain, which are thought to be associated with degenerative changes in the intervertebral disk, represents a major epidemiologic problem. In the United States, back pain is the second leading symptom that prompts visits to physicians. As many as 80% of adults in the United States experience at least one episode of low back pain during their lifetime, and 5% experience chronic problems.^[1]  An understanding of degenerative disk disease is important for managing these patients. (See the images below.)

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The process of disk degeneration following internal disk disruption and herniation.

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The various forces placed on the disks of the lumbar spine that can result in degenerative changes.

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Anatomy

Vertebral anatomy

The spine is composed of seven cervical vertebrae, 12 thoracic vertebrae, five lumbar vertebrae, and a fused set of sacral and vestigial coccygeal vertebrae. Spine stability is the result of three columns in one, as described by Dennis. Fracture or loss of two columns results in instability.

The anterior column consists of the anterior longitudinal ligament and the anterior portion of the vertebral body. The middle column consists of the posterior wall of the vertebral body and the posterior longitudinal ligament. The posterior column is formed by the posterior bony arch; this consists of transverse processes, facets, laminae, and spinous processes.

Intervertebral disks form one quarter of the total length of the spinal column. Each vertebra has the potential for 6° of freedom, translation in all three axes of movement, and rotation around each axis. Not all vertebrae are created equal; the cervical vertebrae have the greatest freedom of flexion, extension, lateral rotation, and lateral flexion. This is because they are larger, they have concave lower and convex upper vertebral body surfaces, and they have transversely aligned facet joints.

Thoracic vertebrae have restricted flexion, extension, and rotation but freer lateral flexion because they are attached to the rib cage, are smaller, have flatter vertebral surfaces, have frontally aligned facet joints, and have larger overlapped spinous processes. The lumbar spine has good flexion and extension and free lateral flexion because its disks are large, the spinous processes are posteriorly directed, and the facet joints are sagittally directed. Lateral lumbar rotation is limited because of facet alignment.

Sensory innervation

The sensory of intervertebral disks is complex and varies according to their location within the spinal column. In the cervical spine, studies by Bogduk^[2] and Mendel^[3]  demonstrated the presence of both nerve fibers and mechanoreceptors within the anulus fibrosus. Impulses from these structures are transmitted via the sinuvertebral nerves and branches of the vertebral nerves. Another study by Bogduk^[4]  found that the sensory innervation of the lumbar intervertebral disks, like that of the cervical disks, is derived from the sinuvertebral nerves but also from branches of the ventral primary rami and rami communicantes.

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Pathophysiology

Of all connective tissues, the intervertebral disk undergoes the most serious age-related changes. By the third decade of life, the nucleus pulposus becomes replaced with fibrocartilage, and the distinction between the nucleus and the annulus becomes blurred. The proteoglycan, water, and noncollagenous protein concentrations decrease, while the collagen concentration increases. The increase in collagen concentration is more pronounced in the nucleus and in the posterior quadrants of the disk. It is more pronounced with age and moves caudally in the lumbar spine (similar to the Wolff law).

Biochemically, aging increases the ratio of keratin sulfate to chondroitin sulfate, and it also changes the proportion of chondroitin-4-sulfate to chondroitin-6-sulfate, with a parallel decrease in water content. Proteoglycan synthesis decreases, which decreases the osmotic swelling and the traffic of oxygen and nutrients to the disk. Because of this decreased traffic, breakdown products of link and noncollagenous proteins stagnate in the disk. Nonenzymatic glycosylation of these breakdown products accounts for the brown discoloration of the aging connective tissues.

Differentiating aging from degeneration is difficult. According to Pearce et al, "[a]ging and degeneration may represent successive stages within a single process that occurs in all individuals but at markedly different rates."^[5]  Aging and degeneration have in common decreased water and proteoglycan content in the disks, combined with increased collagen.

Whereas sagittal alignment, facet joint arthritis, and genetics potentially play a role in intervertebral disk degeneration, the results of one study suggested that the rate of degeneration may be associated with age. Those of African ethnicity also showed a faster rate of degeneration when compared with whites; sex did not show a significant effect on degeneration.^[6]

One study demonstrated that the presence of juvenile disk degeneration was strongly associated with overweight and obesity, low back pain, increased low back pain intensity, and diminished physical and social functioning. An elevated body mass index (BMI) was significantly associated with increased severity of disk degeneration.^[7]

Another study found metabolic syndrome to be four times more prevalent in patients with radiographic evidence of severe degenerative disk disease as defined by degenerative spondylolisthesis or cervical or lumbar stenosis causing neurologic symptoms^[8] .

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History and Physical Examination

The cascade of degenerative changes seen in degenerative disk disease can be subdivided into the following three stages:

• Dysfunction
• Instability
• Restabilization

The duration of the stages varies greatly, and distinguishing the signs and symptoms from one stage to the next is difficult.

The dysfunction stage involves outer annular tears and separation of the endplate, cartilage destruction, and facet synovial reaction. The symptoms of dysfunction are low back pain or neck pain, often localized but sometimes referred, and painful movement. The signs are local tenderness, contracted muscles, hypomobility, and painful extension of the back, neck, or both. Results of a neurologic examination are usually normal.

In the instability stage, disk resorption and loss of disk space height occur. Facet capsular laxity may develop, leading to subluxation. The symptoms are those of dysfunction (ie, "giving way" of the back, a "catch" in the back with movement, and pain with standing after flexion). The signs are abnormal movement (ie, during inspection or palpation), including observation of a catch, sway, or shift when standing erect after flexion. 

In the stage of restabilization, the progressive degenerative changes lead to osteophyte formation and stenosis. The main symptom is low back pain of decreasing severity. The signs are muscle tenderness, stiffness, reduced movement, and scoliosis.

It has been found that the release of cytokines plays a key role in all three stages; this represents a likely target for future therapeutic interventions.

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Laboratory Studies

Seronegative spondyloarthropathies (SNSAs) are common causes of back pain and should be excluded.

Order HLA-B27 (class 1 histocompatibility HLA) testing to assess for ankylosing spondylitis (AS), reactive arthritis (formerly called Reiter syndrome), psoriatic arthritis, and inflammatory bowel–associated arthritis. AS is an inflammatory disease of unknown etiology that affects an estimated 350,000 persons in the United States and 600,000 in Europe, primarily white males in the second through fourth decades of life. Worldwide, the prevalence is 0.9%. Genetic linkage to HLA-B27 has been established. In the United States, 0.1-0.2% of whites are estimated to have AS. HLA-B27 is extremely rare in African Americans.

Serum immunoglobulin A (IgA) is elevated in some patients.

Inflammatory causes of low back pain can be ruled out with tests for acute-phase reactants such as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level. A complete blood count (CBC) should be obtained, including a platelet count.

Rheumatoid factor (RF) testing and antinuclear antibody (ANA) testing are good screening tools for autoimmune disorders.

In rare cases, it may be necessary to exclude gout and calcium pyrophosphate dihydrate deposition by checking serum uric acid and performing synovial fluid analysis to check for crystals.

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Imaging Studies

The role of imaging studies in degenerative disk disease is to provide accurate morphologic information that can be combined with clinical symptoms to guide therapeutic decision making.

Magnetic resonance imaging

The first open magnetic resonance imaging (MRI) scanner was produced by Fonar in 1982. In 1996, Fonar introduced the Stand-Up MRI, a whole-body MRI scanner with the ability to scan patients standing, sitting, bending, or lying down. With its unique ability to scan patients in weightbearing postures, the Stand-Up MRI allows identification of pathologies that are undetected on conventional recumbent MRI scanners, such as lumbar degenerative disk disease with disk herniations. An additional benefit of the Stand-Up MRI is its spacious and nonclaustrophobic geometric design. Patients typically sit comfortably watching a 42-in. television throughout the scanning procedure

MRI can be used to differentiate between the nucleus and the anulus; hence, it allows delineation of contained and noncontained disk herniations. With this information, pathologic disks can be described as protruded disks, extruded disks, or migrated disks.

MRI can show anular tears and the posterior longitudinal ligament. Therefore, it can be used to classify herniations, from simple anular bulging to extruded and free-fragment disk herniations.

Vertebral bodies adjacent to degenerating disks undergo changes, which Modic described as type 1 and type 2 changes. Some hypothesize that trauma to the intervertebral disks releases chemical substances that increase the diffusion resistance through an autoimmune mechanism. As the diffusion coefficient increases, the endplate undergoes sclerosis and the adjacent bone marrow exhibits an inflammatory response (ie, as it is infiltrated by fibrovascular tissue).

These changes (Modic type 1) lead to diminished intensity on T1-weighted images and increased intensity on T2-weighted images. The inflammatory response destroys the marrow of the adjacent vertebral endplates, which is replaced by fat. These changes (Modic type 2) lead to increased signal intensity on T1-weighted images, and the same or increased intensity on T2-weighted images.

MRI is the most comprehensive imaging modality for providing accurate, reliable, and detailed anatomic information in degenerative disk disease. Heuck et al found that clinical information can change the final impression of the radiologist in as many as 25% of cases and should always be considered in reading and reporting MRI findings.^[9]

Computed tomography

In the absence of MRI, computed tomography (CT) is accurate in diagnosing disk herniations because of the contrast between herniated disk material, perineural fat, and the adjacent posterolateral margins of the bony vertebrae. However, MRI remains the imaging modality of choice for diagnosing lateral herniations.

CT offers several advantages over MRI. Among these are lower cost, less stress for claustrophobic patients, and better detection of subtle bony changes (eg, spondylolysis, early degenerative changes of the facet joints). CT is also better for assessing bony integrity after fusion.

Gundry and Heithoff established the following criteria for CT diagnosis of disk herniation with associated neural impingement^[10] :

• First, the disk protrusion must be focal and asymmetric, often dorsolateral in position, directly underlying the nerve root traversing that disk
• Second, nerve root compression and/or displacement should be demonstrable
• Third, postimpingement swelling of the affected nerve root is often present caudal to the herniation; this results in enlargement of the nerve and blurring of its margin because of edema, inflammatory exudates, or prominence of the adjacent epidural veins

Lumbar diskography

Diskography is a controversial procedure. The value of diskography in determining a source of pain or whether surgery is necessary has not been proved. Its validity has been questioned on the grounds of technical errors and false-positive findings. Opponents of the procedure believe that false-positive findings are the result of psychosocial factors and/or neurophysiologic phenomena, such as central hyperalgesia in patients with chronic pain. The existence of clinically significant diskogenic pain is also questioned.

Proponents of diskography believe that it is the only method to diagnose diskogenic pain. They advocate strict selection criteria for patients and strict criteria for a positive diskogram result.

Diskography is used in several clinical situations, including the following:

• Assessment of equivocal abnormalities seen on myelography, CT, or MRI
• Detection of a symptomatic disk among multilevel abnormalities
• Diagnosis of a lateral disk herniation
• Provision of subjective support for the existence of diskogenic pain
• Selection of fusion levels
• Evaluation of the spine after surgery

These uses are not scientifically established.

The aim of diskography is to evaluate whether a disk is painful under certain conditions. The diskogram is less about the anatomy of the disk and more about its pathophysiology. A disk that looks abnormal on MRI may not be painful, whereas a minimally disrupted disk on MRI may be associated with severe pain on a diskogram.

Abnormal disks accept injection of more than 1.5 mL of normal saline or contrast material, with a spongy endpoint during injection. In abnormal disks, contrast material extends beyond the nucleus pulposus through annular tears or through a radial fissure. Because the outer anulus is richly innervated by the recurrent meningeal nerve, the anterior primary ramus, the mixed spinal nerve, and the gray ramus communicans, the pressure of the injected contrast material provokes pain.

When the pressure of the contrast material reaches the part of the disk in contact with the nerve root, radicular pain may be provoked.

Potential complications or adverse effects from diskography include exacerbation of pain, contrast agent allergy, nerve root injury, and chemical or bacterial diskitis.

CT diskography

This procedure should be performed within 4 hours of an initial diskography. Clinical applications include the following:

• Determining whether a disk herniation is contained, protruded, extruded, or sequestrated
• Distinguishing between mass effects from scar tissue or disk material in the spine after spinal surgery

Combination of imaging modalities

A combination of imaging modalities may be necessary to evaluate cervical stenosis and nerve root compression adequately.^[11]

Plain cervical radiographs provide important information on alignment, degenerative bony changes, and deformities. Dynamic flexion/extension images are important to determine sagittal balance and the presence of osseous instability.

After plain radiography, MRI has become the study of choice in the initial evaluation of patients with neck pain. MRI provides images in multiple planes, is noninvasive, and is excellent for studying intrinsic cord disease.

Myelography with postmyelography CT is excellent for evaluating nerve root compression. With reconstructions, it also provides excellent details of the bony anatomy in multiple planes.

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Procedures

Transforaminal selective nerve root blocks (SNRBs) have been used as both subjective diagnostic tools and therapeutic interventions for lumbar spinal stenotic levels. When MRI shows evidence of multilevel degenerative disk disease, SNRBs can be used to determine whether a specific nerve root is affected. The procedure involves injection of anesthetic and contrast at the nerve root level of interest under fluoroscopic guidance. This creates an area of hypoesthesia in the respective dermatome.

Anderberg et al investigated the correlation of SNRBs with MRI findings and clinical symptoms in cervical spines with multilevel degenerative disk disease. They found a 60% correlation with the most severe areas of MRI degeneration. In areas of neurologic deficit, dermatomal radicular pain showed a 28% correlation with SNRB results.^[12]

SNRB can sometimes be a helpful tool together with clinical findings/history and MRI of the cervical spine for preoperative investigation in patients with multilevel degenerative disk disease who present with radicular pain.

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Approach Considerations

Conservative treatment of degenerative disk disease includes the following:

• Back education and back school
• Exercise
• Medications
• Physical modalities
• Injections

Surgical treatment is used in approximately 5% of patients and includes the following:

• Lumbar procedures
• Cervical procedures

Lumbar surgery is indicated in the following patients:

• Those with severe spinal stenosis
• Those with intractable pain
• Those in whom an appropriate 6- to 12-month nonoperative course of treatment fails

Surgery is elective, except in the presence of bowel and bladder symptoms or cauda equina syndrome.

In elective cases, other conservative modalities should have been tried and observed to fail. The patient should be prepared for the operation from a psychological viewpoint. Instability is present at one or two levels (as mentioned above in the instability phase of degenerative changes).

In the case of cervical disk disease with radiculopathy, the indications for surgical treatment are as follows:

• Intractable pain
• Progressive motor or sensory deficit
• Symptoms refractory in a reasonable period of nonoperative therapy

When the symptoms and signs correlate with radiographic evidence of root compression, various groups report a greater than 90% likelihood of a favorable outcome with both anterior and posterior approaches to surgery.

In the case of cervical disk disease with myelopathy, because the natural history is a stepwise worsening course, early surgery to decompress the spinal cord is recommended to arrest progression if the clinical and radiographic changes are well correlated. The best results for myelopathy occur when surgery is performed within 6 months of the onset of symptoms. Some series show improvement of greater than 70% with surgical treatment of patients with myelopathy.

Relative contraindications for spinal fusion include the following:

• Smoking
• Morbid obesity
• Active infection
• Severe medical or psychological problems

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Nonoperative Therapy

Back education and back school

The goal is to teach patients how to help themselves manage their back pain. First, knowledge of normal spine anatomy and biomechanics is taught, together with the mechanisms of injury. Then, the diagnosis is explained to the patient, making use of spine models. The neutral or balanced position, which differs from patient to patient, is sought.

Back school teaches the patient basic body mechanics, such as the correct posture for standing, standing at a desk or drawing board, sitting, brushing teeth, washing the face, pushing and pulling a weight, lifting a weight, getting in and out of bed, sleeping, getting into a car, and sitting in a car. Back school also teaches patients the proper and improper approaches for sitting, bending forward, lying down, coughing, or sneezing when the back is painful.

Exercise

Different types of exercises are prescribed, depending on each patient's diagnosis. Floor exercises consist of abdominal bracing, modified situps, double-knee-to-chest or low back stretches, seat lifts, mountain and sag exercises, knee-to-elbow exercises, hamstring stretches, extension exercises, and extension flexibility exercises. Swimming exercises are some of the best activities for back pain. Aerobic exercises improve endurance if performed regularly (ie, ≥3 times/week). Relaxation exercises are good for relieving muscular tension that may aggravate back pain.

Medications

These include muscle relaxants, nonsteroidal anti-inflammatory drugs (NSAIDs), and analgesics.

Physical modalities

These include the use of ice packs, heating pads, electrical stimulation, phonophoresis, iontophoresis, relaxation, and biofeedback.

Injections

Epidural steroid injections are most commonly used for therapeutic purposes. The type and dosage of steroid employed vary widely. Methylprednisolone (80-120 mg) mixed with normal saline to achieve a volume of 8-10 mL is effective and safe. In some centers, two or three injections are given over a 1- to 2-week course, but long-term results do not appear to be any different from those achieved with a single injection.

The response to epidural injections is variable, and many authorities believe that the injections are only of short-term value. Even if a favorable response occurs, no more than four injections should be given annually. Immediate pain relief may be achieved by adding 4-6 mg of preservative-free morphine to the epidural steroid injection. Pruritus is a reliable sign of epidural placement.

Patients should be observed for 24 hours after morphine epidural steroid injections to look for any respiratory depression or urinary retention, even though these adverse effects are uncommon. If morphine is to be avoided, lidocaine or bupivacaine may be administered in combination with the steroid to achieve immediate pain control, albeit of short duration.

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Surgical Therapy: Lumbar Procedures

The lumbar surgical procedures most commonly performed for degenerative disk disease fall into the following two categories:

• Decompression - This involves removal of bone or disk material from around a compressed nerve root to relieve pinching of the nerves and provide more room for their recovery; the procedure is performed through laminectomy and diskectomy
• Spinal fusion - This involves using a bone graft to fuse one or more vertebrae and stop motion at a painful vertebral segment so as to stop or decrease the pain generated from the joint

Carreon et al evaluated 25 prospective, randomized clinical studies of patients who underwent spinal fusion or nonsurgical treatment for lumbar degenerative disk disease, chronic low back pain, and spondylolisthesis, comparing results after 1-year follow-up.^[13] They found substantial improvement in patients who underwent fusion for degenerative disk disease or spondylolisthesis. Not as much improvement was found in patients with chronic low back pain, but these patients also had lower baseline disability.

A Cochrane review evaluated 33 randomized comparative studies on various fusion techniques, including diskectomy alone, addition of interbody fusion, and addition of anterior plates, for patients with single- or double-level degenerative disk disease.^[14] Few of the studies reported on pain, and thus little or no difference was noted in pain relief between the different procedures. Moderate-quality evidence was found for the following outcomes:

• For iliac crest autograft and metal cage techniques, no significant different was found in Odom’s criteria
• Fusion with bone graft was more effective than diskectomy alone
• Complication rates were not significantly different for iliac crest autograft and diskectomy alone

Lumbar diskectomy

During surgery, the affected level is identified through a posterior midline approach. The incision in the ligamentum flavum is started in the midline, where it is tented away from the dura. The ligamentum flavum is excised in one piece to expose the interlaminar space on one side. The opening is widened by excising portions of lamina. Difficulty in retracting the root suggests that it is compressed by a disk herniation or entrapped in a narrowed lateral recess.

Once the nerve root is identified, it is retracted and a cruciate incision made in the bulging anulus. The loose fragments of the disk are extracted with pituitary rongeurs. The nerve root should be freely mobile and easily retracted, otherwise it may still be compressed or lateral stenosis may be present. In the latter case, the lateral recess and the neural foramen should be enlarged (see below). A free fat graft is placed over the exposed dura to prevent adhesions.

After surgery, a neurologic examination is performed in the recovery room, and the findings serve as a baseline. A urinary catheter is used if difficulties with micturition arise. Postoperatively, the patient may stand and walk for increasing periods. The patient can usually go home 1-5 days after surgery. Some surgeons also perform the lumbar diskectomy as an outpatient procedure.

Low back exercises (pelvic tilting and half-situps) are started at this point. Follow-up initially occurs at 2- to 6-week intervals. Light work is started at 2-8 weeks and heavy work at 12-16 weeks.

Lumbar laminotomy for one-level central and lateral stenosis

The operation involves an approach to the stenotic level through a one-level bilateral minimal partial laminotomy. A gauge is inserted into the lateral canal to determine its size. The medial third of the inferior articular process is removed with an osteotome or rongeur. The medial and anterior parts of the superior articular process are removed with a power tool, a Kerrison rongeur, or an osteotome and mallet. For lateral stenosis, it is usually necessary to remove more of the superior articular process until the lateral canal diameter is 6 mm. At the end of the procedure, a free fat graft is placed between the dura and the posterior muscles to prevent adhesions.

Lumbar laminectomy for multiple-level central and lateral stenosis

If conservative measures fail, the operation is essentially the same as for one-level stenosis. The dura often is exposed just above or just below the lesion through a normal interlaminar space. The aperture is then widened as described above, and the medial portions of inferior and superior facets are removed. The exposure is then lengthened longitudinally with a Kerrison rongeur, with care taken not to injure the dura. The laminectomy should be as short as possible. However, a long laminectomy does not make the spine unstable, provided that the lateral two thirds of all the facet joints are preserved.

Postoperative care is the same as that after diskectomy, but these patients usually experience less postoperative discomfort.

Approximately 70-80% of patients who undergo laminectomies have significant improvement in their function and markedly reduced levels of pain and discomfort. Laminectomy results are much better for relief of leg pain caused by spinal stenosis than for relief of lower back pain.

The risks and complications of laminectomies include the following:

• Nerve root damage (1 per 1,000 cases)
• Bowel/bladder incontinence (1 per 10,000 cases)
• Cerebrospinal fluid (CSF) leakage (1-3%)
• Infection (1%)
• Postoperative instability at the operated level (5-10%)
• General anesthetic complications, such as myocardial infarction, blood clots, stroke, pneumonia, or pulmonary embolism

Lumbar spinal posterolateral gutter fusion

This type of spinal fusion involves placing bone graft material in the posterolateral portion of the spine (a region just adjacent to the spine).

During surgery, a bone graft is harvested from the posterior iliac crest. The posterior articular and transverse processes are completely denuded of periosteum with an elevator. The additional stripping provides more bare bone and stimulates more new bone formation. A sharp curved gouge is used to raise "shingles" of corticocancellous bone on the posterior surface of the transverse process.

Alternatively, a high-speed burr can be used to achieve decortication. The same technique is used for shingling and denuding the upper and posterior surface of the sacrum, for obtaining a free cancellous bone graft. The graft is then placed over and between the denuded surfaces. The large back muscles that attach to the transverse processes are elevated to create a bed on which to lay the bone graft. The back muscles are then laid back over the bone graft, and the tension created holds the bone graft in place. Finally, a free fat graft is placed and sutured over the exposed dura to prevent encroachment onto the bone graft.

Postoperative care is for approximately 5-10 days. A back brace usually is applied.

The two key factors under a patient's control that determine whether a fusion solidifies are (1) smoking cessation and (2) limited motion.

The risks of this type of surgery are as follows:

• Nonunion
• Infection
• Bleeding
• Solid union with no reduction of back pain

Nonunion rates are in the range of 10-40%; risk factors include prior surgery, smoking, obesity, multilevel fusion surgery, and previous radiation therapy for cancer. Infection and bleeding have an occurrence rate of 1-3%.

Posterior lumbar interbody fusion

The advantage of posterior lumbar interbody fusion (PLIF) over anterior lumbar interbody fusion (ALIF) is that either decompression or diskectomy can be performed through the same approach. Unlike posterolateral gutter fusion, PLIF achieves spinal fusion by inserting a bone graft directly into the disk space. An oversized bone graft is harvested from the posterior iliac crest through a transverse incision. The ligamentum flavum is excised completely.

When the operation is for disk disease, the interlaminar space is widened by removing the superior and inferior margins of the adjacent laminae, performing a partial medial facetectomy, and retracting with a laminar spreader. A rectangle of anulus is excised. The bony ledge of the superior margin of the lower vertebral body is removed, clearing the way to the diseased disk. The endplates and disk material are then removed. Blocks of corticocancellous bone taken from the iliac crest are cut to the measured size of the disk space and jammed into place. The same maneuver is repeated on the opposite side. Finally, a free fat graft is sutured to the nearby soft tissues to cover the dura.

Postoperatively, braces are optional.

PLIF has several disadvantages, including the following:

• First, not as much of the disk space can be removed with a posterior approach
• Second, an anterior approach provides for a much more comprehensive evacuation of the disk space and, hence, increased surface area available for fusion
• Third, a much larger bone graft can be inserted from an anterior approach
• Fourth, in cases of spinal deformity (eg, isthmic spondylolisthesis), a posterior approach alone is more difficult to reduce the deformity
• Finally, although the risk is small, insertion of a bone graft posteriorly may allow it to retropulse back into the canal and create neural compression

The major risk for this type of surgery is nonunion. The rates of nonunion are in the range of 5-10%, lower than that for posterolateral gutter fusion.

Lin et al analyzed eight prospective studies (N = 503) involving patients who underwent PLIF, ALIF, or transforaminal lumbar interbody fusion (TLIF) for degenerative disk disease study in order to evaluate the pain and function after surgical treatment.^[15]  They found that minimally invasive PLIF resulted in lower pain scores than open TLIF and open PLIF, as well as lower Oswestry disability index (ODI) scores than open TLIF, ALIF, minimally invasive TLIF, and open PLIF. 

Anterior lumbar interbody fusion

ALIF is similar to PLIF, except that in ALIF, the disk space is fused by approaching the spine through the abdomen instead of through the back.

An anterior retroperitoneal or transperitoneal approach is made, and the main vessels are retracted to the side. A flap of the anterior longitudinal ligament and anterior anulus fibrosus is raised with a scalpel. The disk material is removed piecemeal with curettes and pituitary rongeurs as far as the posterior longitudinal ligament. When the disk is completely cleared posteriorly and laterally, the endplates are excised to bleeding cancellous bone with osteotomes. When bleeding is controlled, iliac crest grafts are punched into the space. The flap of anterior ligament and anulus is replaced and sutured.

Postoperatively, oral intake is delayed until bowel sounds return or flatus is passed. Care is similar to that for other fusions.

One advantage of the ALIF approach is that unlike the PLIF or the posterolateral gutter approaches, it leaves both the back muscles and nerves undisturbed. Another advantage is that placing the graft in the front of the spine puts it in compression, and bone in compression tends to fuse better, according to the Wolff law. However, because of the reliance on compression for achieving solid fusion, osteoporosis is a contraindication for ALIF.

Major risks of ALIF include the following:

• Blood loss from damage to major blood vessels, such as the aorta and vena cava (1-15%)
• In men, retrograde ejaculation
• Nonunion (5-10%)
• Infection
• Bleeding (1-3%)

Transforaminal lumbar interbody fusion

TLIF, a modification of PLIF developed by Harms, has become an increasingly popular treatment for lumbar degenerative disk disease, spondylolisthesis, degenerative adult scoliosis, spinal stenosis, and recurrent disk herniation.^[16]

In TLIF, the approach to the spine is posterior, with access to the disk gained via a path through the far lateral portion of the vertebral foramen. This allows complete removal of the disk and placement of an interbody support transforaminally, with reduced risk of nerve injury, while permitting posterior decompression and interbody fusion.

TLIF has been used since the 1940s for degenerative disk disease. It offers good exposure with decreased risk, especially in repeat cases of spine surgery in which the presence of scar tissue makes PLIF very difficult. PLIF permits good posterior decompression; however, the disk is not removed and the segment is not immobilized efficiently.

TLIF is also a viable alternative to anteroposterior circumferential and anterior lumbar interbody fusion. The approach is either unilateral or bilateral laminectomy with inferior facetectomy, diskectomy, arthrodesis, pedicle screw fixation, and insertion of titanium or carbon fiber cages with autologous bone. The fusion can be single-level or multilevel. The goal is anterior column support and fusion.

The results in a number of published series have shown excellent outcomes with few complications. Complications include the following:

• CSF leaks
• Transient neurologic complications
• Minor wound infections

In some series, radiographic fusion was demonstrated in 74-93% of patients, with no deaths or major hardware failure. Of these patients, 90% said they would have the procedure again. TLIF has become a safe technique for interbody support with good clinical outcome.

Preoperative care and postoperative care are the same as for PLIF.

Lateral lumbar interbody fusion

In lateral lumbar interbody fusion (LLIF), also sometimes referred to as extreme lateral interbody fusion (XLIF), the disk space is accessed via a lateral retroperitoneal transpsoas corridor.^[17] It is best suited to conditions that require access to the interbody disk space from T12-L1 to L4-L5. Neuromonitoring is essential for the access to the disk space.

LLIF can be performed with rapid postoperative mobilization, and it is capable of achieving aggressive deformity correction with high fusion rates and comprehensive disk space clearance.^[17] However, it is associated with a risk of possible lumbar plexus, psoas muscle, or bowel injury, particularly at the L4-L5 level. Vascular injury may occur as well and may be difficult to control.

Oblique lumbar interbody fusion

Oblique lumbar interbody fusion (OLIF) involves a minimally invasive approach to the disk space by way of a corridor between the peritoneum and the psoas.^[17] It is similar to LLIF in several respects, but it does not dissect or traverse the psoas. It is suitable for levels from L1 to S1. Neuromonitoring is not required.

Like LLIF, OLIF can be performed with rapid postoperative mobilization and can achieve aggressive deformity correction with high fusion rates and comprehensive disk space clearance.^[17] Because dissection is performed anterior to the psoas, injury to the lumbar plexus or the psoas is unlikely. However, OLIF carries a risk of possible sympathetic dysfunction or vascular injury.

In a study of 36 patients who underwent either standalone OLIF (n = 17) or PLIF (n = 19) for revision of rostral adjacent segment disease (ASD) after previous posterior lumbar fusion, Zhu et al compared the two groups at 1 week, 3 months, and 12 months with respect to operating time, intraoperative hemorrhage, duration of bed rest, and length of hospital stay.^[18]  The OLIF group had less intraoperative blood loss, as well as shorter operating times, bed rest times, and hospital stays. OLIF was found to be effective and safe in this setting and to be superior to PLIF in terms of perioperative parameters, short-term clinical outcomes, and restoration of disk height while yielding similar fusion and reduction rates.

Spine fusion instrumentation

Bone tends to fuse better in an environment with as little motion as possible. The role of spine fusion instrumentation is to decrease motion at the segment undergoing fusion and to provide additional spinal stability.

The three major types of spine surgery instrumentation are as follows:

• Pedicle screws
• Anterior interbody cages
• Posterior lumbar cages

Pedicle screws provide a means of gripping onto a vertebral segment and limiting its motion. Anterior interbody cages are devices inserted into the lumbar disk space through an anterior approach. They can be made of allograft bone, titanium, or carbon/polyetheretherketone (PEEK) (radiolucent cages). Posterior lumbar cages are also made to be inserted into the lumbar disk space, but they are modified to be inserted through a posterior approach. They can be made from the same materials as the anterior cages.

Total disk arthroplasty (replacement)

Total disk arthroplasty (TDA; or total disk replacement [TDR]) is an alternative to lumbar fusion and has been used for lumbar diskogenic pain, with and without radicular symptoms. The main objective of an artificial disk is to replace a painful disk while maintaining the natural anatomic structure of the spine. Devices that have been used in the United States and elsewhere include the Charite, ProDisc, Maverick, and Flexicore disks. Indications for implantation of an artificial disk are quite similar to those for lumbar spine fusion and include the following:

• Degenerative disk disease (typically at a single level)
• Age of 18-60 years
• Major symptom of lower back pain rather than leg pain
• Minimum of 6 months of conservative treatment
• Patient is a candidate for spine surgery (eg, lumbar fusion)

The two types of artificial disks are (1) a total disk prosthesis, designed to replace a full disk, and (2) a nuclear prosthesis, designed to replace the soft inner core of a disk.^[19]  The outer shell of the disk is made of metal, and the inner core is made of rubber polyethylene.

The ProDisc prosthesis has been used for both single-level and multilevel degenerative disease. Bertagnoli et al, in a 2-year study of patients older than 60 years, showed a 94% satisfaction rate with the ProDisc therapy. Patients also showed a decrease in radicular pain. Patients with decreased bone mineral density underwent a vertebroplasty before insertion of the ProDisc.^{[20, 21]} However, the accuracy of certain studies on ProDisc has been challenged.^[22]

One study compared the results of surgical intervention with the ProDisc II prosthesis with nonsurgical rehabilitation in patients with chronic low back pain after 2-year follow-up.^[23] Whereas both methods achieved substantial improvement, the surgical group experienced improved low back pain, patient satisfaction, Short Form (SF)-36 physical component score, and self-efficacy for pain over the nonsurgical group; however, the improvement did not surpass the study’s predetermined “minimally important clinical difference” between the two groups. Surgical risks should be considered in deciding a course of treatment.

Tropiano et al showed that the sex of the patient and whether surgery was multilevel did not affect the outcome, but prior lumbar surgery or age younger than 45 years was associated with slightly worse outcomes.^[24]  Complications were very few and included a unilateral foot drop, implant subsidence, and loss of vibration and proprioception. These complications were seen mainly in patients with circumferential spinal stenosis.

In a prospective single-center clinical study of the use of ProDisc II to teat low back pain from lumbar degenerative disk disease that did not respond to conservative therapy, Siepe et al found that this approach yielded satisfactory results that were maintained at a mean follow-up of 7.4 years.^[25]

Lu et al, in a study of 32 patients treated with the Charite III device and followed for a mean of 11.8 years, reported a cumulative survival of 100% and documented satisfactory clinical and radiologic results that were maintained at follow-up.^[26] The rate of reoperation and the incidence of complications were deemed acceptable as well.

In 2015, the International Society for the Advancement of Spine Surgery (ISASS) concluded that sufficient scientific evidence had been accumulated to support the safety and efficacy of single-level lumbar TDA for patients who met well-established selection criteria.^[27]  The ISASS noted that data from prospective randomized clinical trials indicated consistently low rates of reoperation, as well as extremely low levels of particulate wear debris complications.

Smoking and risk of pseudoarthrosis (surgical nonunion) after fusion procedures

Smoking is well known to impede bone and wound healing. Brown et al investigated the rate of pseudoarthrosis in persons who smoke and in persons who do not smoke who had undergone a two-level laminectomy and fusion of the lumbar spine over a 1-year period. Of 100 patients, 40% of those who smoked and 8% of those who did not smoke developed a pseudoarthrosis. The results clearly show that smoking causes a significant increased risk for pseudoarthrosis in spine fusions and is a major contraindication for surgery.

• References

Surgical Therapy: Cervical Procedures

The goal of surgery for cervical radiculopathy is to achieve adequate decompression of the nerve roots. The options available are as follows:

• Anterior cervical diskectomy (ACD)
• ACD and fusion (ACDF)
• ACDF with internal fixation (plating)
• Posterior foraminotomy

The choice of the appropriate procedure depends on a number of factors, including the location of the neural compression, the presence of deformity or instability, and potential morbidity. In general, anterior pathology, such as a centrally herniated disk and anterior osteophytes, is treated anteriorly, and posterior pathology, such as posterolateral osteophytes/disk herniations, may be treated with a posterior approach.

The goal of surgery for degenerative cervical disk disease with myelopathy is to decompress the spinal cord adequately. The literature on spondylotic myelopathy does not clearly demonstrate the superiority of either the anterior approach or the posterior approach. Options for surgery include the following:

• Single- or multiple-level ACDF
• Single- or multiple-level anterior corpectomy with fusion
• Laminectomy with or without fusion
• Laminoplasty

The choice of approach is based on the location of the pathology, the risks and benefits of each procedure, and the geometry of the spinal canal.

Procedures for patients with radiculopathy

Anterior cervical diskectomy

ACD involves performing a decompression of the nerve roots through an anterior diskectomy. An area of controversy is whether an interbody fusion is necessary after a single-level ACD. Although initially ACD involved fusion procedures, complications, including graft and donor-site complications, prompted some surgeons to perform a simple diskectomy. Diskectomy may be considered for patients with normal cervical lordosis, minimal axial pain, and abnormalities limited to one level. A high frequency of improvement has been reported in the literature with diskectomy alone, although most surgeons now routinely use fusion.

Possible risks and complications of ACD include the following:

• Nerve root damage
• Damage to the spinal cord (~1 per 10,000 cases)
• Bleeding
• Infection
• Graft dislodgment
• Damage to the trachea or esophagus
• Continued pain

Damage to the recurrent laryngeal nerve during the procedure may cause hoarseness, and retraction of the esophagus sometimes causes temporary difficulty with swallowing.

Anterior cervical diskectomy and fusion

An interbody fusion usually avoids recurrent radiculopathy from foraminal narrowing and the possibility of developing late kyphosis from disk-space collapse. A combination of diskectomy and fusion should be performed in all patients, especially if multiple levels are involved or if instability is documented at any level. The complications involved with not performing a fusion are much higher than the small risk of complications associated with fusion.

For single-level fusion, autologous bone results in a fusion rate of 95%. To prevent donor-site complications, alternatives include the use of allograft bank bone, bovine cancellous bone, and synthetic materials. The main risk of a fusion surgery is that it does not result in fusion. In general, allograft bone does not heal quite as well as autograft bone, but both yield good results when used in the anterior cervical spine.

If a graft is used without instrumentation, the risk of graft dislodgment or extrusion is 1-2%. If this happens, another operation is performed to reinsert the bone graft, and instrumentation (plating) can be used to hold it in place.

Anterior cervical diskectomy and fusion with internal fixation (plating)

Plating can be helpful in patients who require procedures in multiple levels, with documented instability, in persons who smoke, patients with a prior history of nonunion, and those with a previous fusion adjacent to the level to be fused. In addition, with a plate, no brace is needed, allowing an earlier return to work and resumption of daily activities.

Kaiser et al found the overall fusion rate for 522 patients for one-level ACDF with allograft bone and anterior plate to be 96%. This rate decreased to 91% when the procedure was performed over two levels. The rates for one- and two-level fusions without anterior fixation were, respectively, 90% and 72%. The improved fusion rates and low complications associated with anterior cervical plating are good arguments for its use in the treatment of degenerative cervical disk disease.^[28]

Posterior cervical foraminotomy

Nerve root decompression may be accomplished posteriorly by performing a foraminotomy. The keyhole approach, developed by Scoville to decompress nerve roots, involves removal of one or more hemilaminae with removal of osteophytes and disk fragments. This is used most commonly in soft posterolateral disk herniations, thus obviating the need for a fusion. High success rates have been reported.

Lawton et al looked at 38 patients who had undergone cervical microendoscopic foraminotomy and cervical microendoscopic diskectomy and found that there was a statistically significant reduction in pain and disability at 1, 2, and 3 years post operation.^[29]

Procedures for patients with myelopathy

Single- or multiple-level ACDF

ACDFs at single or multiple levels may be performed for myelopathy when the pathology is limited to the disk spaces and does not involve the vertebral bodies. Although multilevel corpectomy is also an option in these cases, multilevel ACDFs have the advantage of segmental fixation and restoration of lordosis.

Jackson et al evaluated 7-year neurologic and clinical outcomes of patients with multilevel cervical degenerative disk disease who were treated at two contiguous levels with either TDA or ACDF and followed for 7 years.^[30]  They found that two-level TDA yielded better long-term neurologic outcomes than ACDF did. The TDA group had less neurologic deterioration, a reduction in adverse events, fewer subsequent surgical procedures, and decreased neck and arm pain, while maintaining range of motion.

Single- or multiple-level cervical corpectomy with fusion

Corpectomy is the removal of a vertebral body and the disk spaces at either end in an effort to completely decompress the cervical canal.

With multiple areas of spondylotic compression of the spinal cord, corpectomy with strut grafting may be performed. With multilevel corpectomy, anterior strut fusion is necessary to prevent kyphotic deformity and to restore stability. Anterior plating is recommended for corpectomy and multilevel procedures to reduce the risk of graft extrusion and pseudoarthrosis. As the length of the fusion increases, the rates of both graft- and instrumentation-related complications increase. In such cases, posterior stabilization is recommended to improve stability and fusion rates and reduce graft- and instrumentation-related complications.

Corpectomy is a more technically difficult surgical procedure. The risks are similar to those for diskectomies, but because a corpectomy is a more extensive procedure than a diskectomy, the risks are greater. The most worrisome risk is compromise of the spinal cord leading to quadriplegia. To decrease this risk, spinal cord function can be monitored during surgery using somatosensory evoked potentials.

Another risk is compromising the vertebral artery, which can cause a stroke.

Cervical laminectomy with or without fusion

Laminectomy is sometimes needed if patients have congenital cervical stenosis or if the disease process involves more than three levels or multiple discontinuous levels. In patients with kyphosis, anterior fusion may be needed to prevent further progression of the kyphotic deformity. If most of the compression of the spinal cord is posterior, laminectomy can sometimes be used.

As with cervical corpectomy, the main risk with cervical posterior laminectomy is deterioration in neurologic function after surgery. Use of intraoperative somatosensory evoked potentials can decrease this risk. Other risks include dural tear, infection, bleeding, increased pain, and instability in the spinal column.

If a laminectomy is performed, a fusion is recommended to prevent kyphotic progression. Other indications for posterior fusion include evidence of instability on preoperative dynamic radiographs, failure of anterior fusion, or decompression involving bilateral facetectomy. Most of the experience with posterior fusion has been with autologous bone from spinous processes or the iliac crest, but allograft bone has been used.

Cervical laminoplasty

The laminoplasty technique was developed by Japanese surgeons primarily for treatment of ossification of the posterior longitudinal ligament. It involves osteoplastic enlargement of the spinal canal by performing the laminectomy on one side to create a "door." The goal of this procedure is to reduce the postlaminectomy instability discussed previously. Although infrequently used, successful treatment of cervical spondylosis has been reported with this technique.

Other procedures

Cervical keyhole foraminotomy

Posterolateral keyhole foraminotomy is indicated for posterolateral disk herniations with radicular pain. It is an efficient way of decompressing a lateral soft disk without the risks of an anterior approach. A bone graft is not needed. Use of an operative microscope helps achieve good outcomes. Burke and Caputy described a rigid endoscopic approach with a smaller incision, less postoperative pain, and fewer complications.

Chen et al compared spine segment flexibility after the keyhole procedure with an ACDF and anterior foraminotomy with a diskectomy, and showed a minor increase in motion with the keyhole foraminotomy.^[31]

In a 6-year long-term follow-up study, Silveri et al reported excellent results with preoperative pain relief in all patients and no significant complications. Preoperative and postoperative care is the same as with ACDF.^[32]

Dynamic cervical implant arthroplasty

The dynamic cervical implant arthroplasty is a device that is used to achieve anterior decompression without cervical fusion. The second generation of implants, which comes in three heights and four different models, has been used since 2008 and was primarily developed to overcome the disadvantages of fusions in a less invasive manner and to enable normal motion and preserve biomechanics. In addition, the device results in some limitation of rotation and translation thereby preventing further degeneration of the small joints.

Zhonghai et al, in a stduy comparing the efficacy of the dynamic cervical implant with that of ACDF, found no statistically significant difference in postoperative outcomes but did find that the dynamic cervical implant arthroplasty resulted in better overall cervical range of motion (ROM) and segmental ROM at the treated level as compared with ACDF.^[33] They suggested that the dynamic cervical implant was an effective, reliable, and safe procedure for the treatment of cervical degenerative disk disease.

• References

Other Therapies

Chemonucleolysis with chymopapain or collagenase

The posterolateral extradural approach with a two-plane image intensifier avoids penetrating the dura and causing leakage of chymopapain into the subarachnoid space. Because anaphylactic shock is a potential complication, cardiopulmonary monitoring is used. Additionally, an intravenous line is established; hydrocortisone, epinephrine, aminophylline, and diphenhydramine should be available, and an anesthetist should be present with intubation and ventilation equipment.

The use of contrast material is kept to a minimum, and the chymopapain must be refrigerated until the time of use. The dose is 4000 U or 2 mL per disk.

Postoperatively, the patient should be as active as possible. A stiff canvas corset,^[34]  oral analgesics, and anti-inflammatory drugs are prescribed. Many patients require a few days of in-hospital care.

Because of complications and effectiveness problems, chymopapain injection is rarely performed in current practice.

Automated percutaneous lumbar diskectomy

Onik et al introduced automated percutaneous lumbar diskectomy (APLD) in 1985. This procedure is safer than chymopapain intradiskal injection. It allows debulking of the central disk material by placement of a needle and the use of an automated suction/cutting device. At this time, no clear evidence suggests that APLD is more effective than noninvasive methods of treating disk herniation.

Arthroscopic microdiskectomy

With arthroscopic microdiskectomy (AMD), the surgeon can visualize the nerve root and anulus with an endoscope. Disk fragments in the posterior disk area can be removed using manual and automated instrumentation.^[35]  Biportal AMD has been attempted for improved surgical control (similar to joint arthroscopy), but this variant carries more risk of injury of the nerve root on the contralateral side.

APLD and AMD are recommended primarily for contained disk herniations when noninvasive methods have failed, though attempts have been made to address noncontained lateral disk herniations using AMD instead of the usual paralateral surgical approach.

Microendoscopic diskectomy

This diskectomy uses a posterior approach identical to standard lumbar diskectomy or microdiskectomy. A cannula is docked under the lamina under fluoroscopic guidance and laminotomy. Ligament removal and diskectomy are then performed using an endoscope. Migrated disk fragments are accessible with this technique.

Intradiskal electrothermal anuloplasty

Intradiskal electrothermal anuloplasty (IDET) is a minimally invasive outpatient surgical procedure. After the intervertebral disk is accessed under fluoroscopic guidance, an electrothermal catheter (heating wire) is passed into the posterior anulus of the painful lumbar disk.

Candidates for IDET include patients with back pain caused by small herniations, internal disk tears, or mild disk degeneration, limited to one or two levels. IDET is performed after 6 months of conservative treatment has failed.

Factors predicting successful outcome with IDET are (1) single-level disk disease, (2) good catheter placement at the time of the procedure, and (3) an absence of secondary gain issues (eg, financial gain from pending litigation or workers' compensation).

IDET is a very safe procedure with a very low risk of complications. Disk-space infection and nerve injury occur in fewer than 1% of patients.

• References

Complications

The complications of lumbar disk surgery are described above. Other complications include cauda equina syndrome, thrombophlebitis, pulmonary embolism, wound infection, pyogenic spondylitis, postoperative diskitis, dural tears, nerve root injury, CSF fistula, laceration of the abdominal vessels, and injury to abdominal viscera. Paralysis, stroke, and death, though rare, are possible.

Two types of postfusion stenosis are described. The most common type is above the fusion, secondary to degenerative changes, and the second type is deep to the fusion, secondary to new bone formation. Degenerative stenosis above the fusion is relieved by decompression through a bilateral laminectomy. Stenosis beneath the fusion requires exposure of the dura above the fusion and removal of the central portion of the fusion mass in a caudal direction.

The most commonly seen lesions in the previously operated back are lateral spinal stenosis (58%), central spinal stenosis (7%), arachnoiditis (16%), recurrent disk herniation (12%), and epidural fibrosis (8%). Arachnoiditis, intraspinal fibrosis, and epidural adhesions may benefit from epidural steroid injections or from a caudal block. If an operation is undertaken again, the distortion of the anatomy, the scar tissue posterior to the dura, and the adhesions between the dura increase the risk of opening of the dura and damaging nerves or blood vessels.

The possible sources of pain in the previously operated spine are many, and they frequently coexist. Possibilities include persistent or recurring disk herniation, diskogenic pain, instability, pseudoarthrosis, lateral recess stenosis, painful motion segment adjacent to a fused motion segment, posterior joint syndrome, sacroiliac joint syndrome, myofascial syndrome, deconditioning of lumbar paraspinal muscles, arachnoiditis, epidural fibrosis, pain at the bone graft donor site, and psychological magnification and causation of pain.

Mannion et al looked at four randomized controlled trials that examined 355 patients and the influence of spinal fusion on adjacent segment disk height as an indicator for disk degeneration.^[36]  They found that at 13 years, disk space height at the adjacent segment was lower, but this reduced disk height had no influence on patient self-rated outcomes, including pain and disability.

A number of complications associated with ACD have been reported in the literature. Fortunately, serious complications are rare (3%). Injury to the recurrent laryngeal nerve, especially with right-side approaches, is the most common complication, though it may be transient. Other structures at risk include the trachea, esophagus, carotid artery, sympathetic chain, and vertebral artery, if the decompression is carried too far laterally. Spinal cord or nerve root injury is the most serious complication but is relatively rare (0.2%) in the hands of experienced surgeons. The C5 nerve root is sensitive to trauma. Other less frequent complications include infections, CSF leaks, and dural tears.

Graft complications after ACDF include collapse, displacement, and pseudoarthrosis. The rate of graft displacement is reported to be as high as 8%. Graft placement under compression and use of plates may reduce this complication rate. Graft collapse is more frequent in patients with osteoporosis. Allograft is preferable if any question exists regarding the quality of the autologous bone. Pseudoarthrosis rates of 5% for a single level and 12-15% for multiple levels have been reported.

Complications reported for ACDF with internal fixation (plating) include hardware failure, screw pullout, or breakage with esophageal perforation.

The most serious complications of foraminotomy are nerve root injuries (4%).

Worsening of symptoms with laminectomy for myelopathy occurs in 3-5% of cases. Postlaminectomy instability and kyphosis have been reported in the range of 10-22%. The role of facetectomy in postoperative instability has been documented in the literature through laboratory and clinical data. Facetectomies of more than 50% cause a significant loss of stability in flexion and torsion compared with an intact spine. Progressive postlaminectomy kyphosis may require anterior corpectomy/strut grafting with instrumentation and, possibly, posterior instrumentation.

• References