Significant dysfunction and progressive disability are the norm, although a large percentage of patients are able to maintain employment and productivity. After a decade of disease, a clinically significant sagittal plane deformity will develop in approximately half of the patients with AS.⁶ Nevertheless, disability increases with disease severity, as do costs associated with advancing disease.⁷ Patients with AS are more likely to have never been married, more likely to be divorced, and more than twice as likely to be work-disabled than members of the general population. As would be expected, individuals with physically demanding occupations and lower educational status are at greater risk for work disability.⁸ Women with AS are also less likely to have had children than women in the general population.⁹

Enteropathic Arthritis

Inflammatory bowel disease is a collective term that includes the conditions of ulcerative colitis and Crohn’s disease. These conditions are associated with arthropathy in 10% to 20% of patients. In fact, the arthropathy may precede the symptoms of bowel disease by a decade or more.

When present, peripheral symptoms often follow the course and severity of the underlying bowel disease. The spondylotic symptoms, however, remain independent of bowel disease.

The features of enteropathic arthropathy are most similar to AS, both clinically and radiographically. However, patients with enteropathic arthritis more commonly have peripheral joint involvement (10% to 20%), followed by sacroiliitis (10%) and spondylitis (3% to 4%).

Psoriatic Arthritis

Genetic, environmental, and immunologic factors are believed to play a role in the development of this disease, although the specific etiology is not well understood. At least 40% of patients with psoriasis are found to have radiographic evidence of inflammatory arthritis,⁸ and significant disability may develop in patients with psoriatic arthritis, with up to 20% demonstrating a rapidly progressive, debilitating clinical course.¹⁰ Psoriatic arthritis is a clinical diagnosis and involves the findings of inflammatory arthropathy and psoriatic skin lesions.¹¹ See Table 281-2 for discussion regarding the clinical features of inflammatory back pain and arthritis.

Psoriatic arthritis may be associated with obesity, hypertension, dyslipidemia, and insulin resistance because of the shared inflammatory pathway.¹²

Reactive Arthritis and Reiter’s Syndrome

“Reactive” arthritis develops as a systemic reaction to infection in another site in the body, commonly after urogenital or enteric infection. Bacteria associated with such diseases include enteric and venereal pathogens such as Shigella, Salmonella, and Chlamydia species. Bacterial DNA and RNA have been identified in synovial fluid, as well as in peripheral white blood cells.

Reiter’s syndrome is a form of reactive arthritis associated with the classic triad of urethritis, conjunctivitis, and arthritis and is typically seen in young men, but it may develop at any age. The lower extremities are most affected, and unilateral SI joint involvement is noted (as opposed to bilateral involvement in AS and enteropathic arthritis). The frequency of spinal involvement is significantly less than with AS, and it typically does not make its way up to the cervical spine. It also tends to be discontinuous in its radiographic appearance, with affected areas being noted to be spaced between normal-appearing areas. Finally, nonmarginal syndesmophytes are observed, again in contrast to AS.

Urethritis often develops first, typically 2 to 4 weeks after infection, followed by conjunctivitis and later arthritis. Most patients have severe symptoms lasting several months. Approximately 15% to 50% have recurrent bouts of arthritis. Chronic disease is found in 15% to 30% of patients.

Pathophysiology

The spondyloarthropathies are noted to affect insertions of muscular and ligamentous tissues into bone, or entheses, thereby leading to the term enthesopathy. Ossification is observed at such sites, as well as at the level of the annulus fibrosus and zygapophyseal joints, and leads to progressive ankylosis. Ossification also occurs in heterotopic locations, such as within the hip musculature after total hip arthroplasty.

The underlying inflammatory process involves T cells and cytokines, including tumor necrosis factor-α (TNF-α).^13,¹⁴ Matrix metalloproteinase-3 (MMP-3) is an enzyme thought to be related to pathogenesis and is also used as a disease marker.¹⁵ AS has been found in association with conditions such as multiple sclerosis, thus raising the possibility of a common pathway to disease.¹⁶

Although the link between infection and arthritic disease is most clear in reactive arthritis, a link is suggested in the other spondyloarthropathies as well. Klebsiella IgG is found in increased levels in patients with AS.¹⁷

Muscle biopsy studies in patients with AS show evidence of abnormal, atrophied types I and II muscle fibers.¹⁸ Whether this contributes to the development of disease or is a result of the disease itself is unclear.

HLA-B27–restricted T cells have been implicated in the development of reactive arthritis as a response to bacterial infections. The HLA-B27 gene is strongly associated with the conditions, but it has a variable association with each subtype. Its strongest link is in white male patients with AS, in whom it is found 90% of the time. The prevalence of the gene is 8% in the general white population and 4% in the African American population. It is more common in regions further from the equator.¹⁹

AS develops in approximately 1% to 2% of people with HLA-B27. This risk increases to approximately 20% to 30% when a first-degree relative carries the diagnosis.²⁰ It is likely that AS is actually more common than has been reported to date.

Overproduction of bone morphogenetic protein-2 (BMP-2) and BMP-7 has been noted in patients with AS, and serum BMP-7 levels can reflect radiographic damage.²¹ The processes leading to bone fusion and the links between inflammation and bone formation remain poorly defined.²² Current research into further susceptibility genes and inflammatory mediators provides hope for greater understanding and treatment options. HLA-60 is another susceptibility gene that may have a role.

Clinical Findings and Diagnosis

Involvement of the axial skeleton more than the appendicular skeleton is characteristic. Extraskeletal manifestations include involvement of the eyes, skin, and cardiovascular system. Fever, weight loss, and systemic symptoms may be seen in periods of active disease.

The spondyloarthropathies have somewhat variable clinical findings, depending on the subtype. Table 281-1 outlines some of these variations. In general, AS tends to be seen in the younger male population.

TABLE 281-1 Differentiating Features of the Spondyloarthropathies

A combination of history and findings on physical examination, along with imaging and laboratory tests, is used in the diagnosis of these conditions. Although advanced disease may have obvious hallmarks, early disease may be subtle. Multiple validated systems have thus been developed to assist in the stepwise analysis of patients, such as the European Spondyloarthropathy Study Group (ESSG) criteria (Table 281-2) and the Amor criteria. The Modified New York criteria (Table 281-3) and the Rome criteria are used specifically for the diagnosis of AS. Although the ESSG criteria have been found to be the most sensitive for spondyloarthropathy and inflammatory back pain, the Modified New York criteria are the most specific for AS.²³ Patients are evaluated for features of inflammatory back pain, as opposed to mechanical back pain (which may be acute in onset or associated with activity and radicular symptoms). The most specific symptoms include pain during the second half of the night, early morning stiffness lasting 30 minutes, alternating buttock pain (referred from the SI joints), and improvement with exercise, not rest (Table 281-4).

TABLE 281-2 European Spondyloarthropathy Study Group Criteria for Spondyloarthropathies

TABLE 281-3 Modified New York Criteria for Ankylosing Spondylitis

TABLE 281-4 Inflammatory versus Mechanical Back Pain

FEATURE	INFLAMMATORY	MECHANICAL
Night pain	+	−
Morning stiffness	+	−
Sacroiliac referred buttock pain	+	±
Radicular pain	−	+
Improves with	Activity	Rest

Patients with spinal deformity will typically have had disease for a decade or more. Such patients complain of difficulty maintaining forward gaze (horizontal gaze) while walking and note difficulty especially when going up an incline or stairs. Although kyphotic sagittal imbalance is typical, coronal plane deformity may occur as well. Advanced deformity with a chin-on-chest appearance creates issues related to hygiene because patients are unable to access their anterior neck skin folds.

On physical examination, patients are noted to have stiffness, muscular atrophy, and potentially a kyphotic posture (depending on the stage of the disease). The Schober test measures thoracolumbar spinal excursion. It is performed by marking a 15-cm length of skin extending from 10 cm above the lumbosacral junction to 5 cm below. The patient is then asked to flex, and in a patient with significant stiffness, the length should not increase more than 5 cm. Of course, this test is not specific to AS.

Chest excursion of less than 3 cm between inspiration and expiration suggests advanced costovertebral involvement and, although highly specific, is not useful in early disease.

Appendicular skeletal disease is associated with peripheral joint involvement, most commonly in the hips and shoulders. Patients with kyphosis attempt to restore sagittal balance through hip extension, knee flexion, and ankle plantar flexion.²⁴ Having said this, hip flexion contractures by and of themselves can be a significant source of sagittal postural imbalance. As a hip flexion contracture develops, patients adopt a forward-flexed posture that may exaggerate the appearance of the kyphosis. Evaluation of the hips is crucial in arriving at an accurate assessment of the degree of spinal deformity that may be present.

Extraskeletal disease involves multiple organ systems, with each subtype of spondyloarthropathy having a somewhat different predilection for each. Such disease includes cardiovascular disease, more specifically aortic insufficiency and conduction disturbances; pulmonary disease, such as apical pulmonary fibrosis; deposition disease, such as amyloidosis with its associated renal dysfunction; and neurological disease such as encephalitis, transverse myelitis, and peripheral neuropathy.²⁵

Neurological deficits may arise as a result of spinal stenosis, upper cervical instability, and chronic inflammation. Ossification of the posterior longitudinal ligament (PLL) in association with AS has been noted and contributes to the acquired stenosis. Because the upper cervical spine tends to lag behind in bony ankylosis, compensatory hypermobility may develop and result in neurological complications. Cauda equina syndrome may be seen, perhaps as a result of chronic inflammation, demyelination, and fibrosis, along with the development of arachnoid diverticula.²⁶

It should be noted that although laboratory tests may reveal an elevated erythrocyte sedimentation rate in 70% of patients and elevated alkaline phosphatase in 50%, there is no laboratory-based diagnostic test for these conditions. Testing for HLA-B27 is not required for diagnosis, and a large percentage of patients test negative for the gene.

Imaging

Characteristic findings are noted on radiographic imaging, and the extent of such findings has been found to correlate clinically with patient spinal mobility and function.^27,²⁸

One of the hallmarks of AS is the “bamboo spine” (Fig. 281-1). As marginal syndesmophytes form along the intervertebral disks, the spine takes on the appearance of a single long bone (contributing to the loss of flexibility and increased risk for fracture). Marginal syndesmophytes are differentiated from (1) osteophytes, which do not typically bridge the disk space, and (2) nonmarginal syndesmophytes, which extend beyond the margin of the disk and spinal column, as seen in diffuse idiopathic skeletal hyperostosis. “Squaring” of the vertebral bodies occurs as the end plates lose their concavity, probably related to chronic inflammation. These spinal changes typically begin distally within the lumbar spine and progress slowly cephalad.

FIGURE 281-1 “Bamboo spine” seen in a lateral view of the cervical spine in a patient with ankylosing spondylitis. Note the bridging syndesmophytes (long arrow) and fused zygapophyseal joints (short arrow).

SI fusion is another hallmark and is required for diagnosis by the New York criteria (Fig. 281-2). It is typically observed before other radiographic changes. Earlier in the disease, erosions are noted at the lower end of the joint, especially over the iliac side. Erosive changes may be seen at the symphysis pubis (osteitis pubis). As ossification progresses along entheses such as the iliac crests, ischial tuberosities, and femoral trochanters, a process known as “whiskering” is observed.

FIGURE 281-2 Bilateral sacroiliac joint fusion in a patient with ankylosing spondylitis.

Spondylodiskitis is characterized by an inflammatory, erosive process of the intervertebral disk, commonly at the thoracolumbar junction. It is unknown whether this erosion represents an area of persistent inflammation, failure of ankylosis across an area of high mechanical stress, or an area of nonunion after trauma to the already ankylosed spine.²⁹ Approximately 5% of patients with AS have been shown to have spondylodiskitis, but only half of these patients tend to be symptomatic.³⁰ Radiographically, spondylodiskitis appears similar to chronic infectious diskitis, with end-plate erosion and surrounding bony sclerosis. Frequently, anterior widening of the disk space is noted.

Enteropathic arthritis has radiographic features similar to those of AS. In contrast, Reiter’s syndrome and psoriatic arthritis typically result in noncontinuous spondylitis, nonmarginal syndesmophytes, and asymmetrical SI joint involvement.¹

Computed tomography (CT) shows similar changes but in greater bony detail. Extensive changes may be noted at the costovertebral articulations (Fig. 281-3). Magnetic resonance imaging (MRI) may show marrow signal alterations secondary to chronic inflammation in this region (Fig. 281-4).^31,³²

FIGURE 281-3 Axial computed tomography scan of the thoracic spine showing bilateral symmetrical involvement of the costovertebral articulations.

FIGURE 281-4 Magnetic resonance image of the thoracic spine demonstrating inflammatory marrow signal changes corresponding to changes on computed tomography (CT). This was mistaken for metastatic disease, and the patient underwent CT-guided biopsy of the “lesion.”

Ossification of the PLL has been observed in association with increasing age and has variable ethnic prevalence.³³

Radiologic methodologies for assessing the extent of spinal involvement have been proposed and are in use.³⁴^–³⁶ These methods have been helpful in assessing the efficacy of treatment regimens in both the research and clinical fields, which was previously hampered by an inability to objectively gauge a patient’s progress. Such instruments include the Stoke Ankylosing Spondylitis Spine Score (SASSS) and the Bath Ankylosing Spondylitis Radiology Index (BASRI).

Methods specific to enthesitis that focus on the ligamentous and muscular insertions at the level of the Achilles tendon, femur, and humerus have been used.³⁷

Peripheral joint involvement is seen most commonly in the hips and shoulders.

Bone mineral density is reduced because of a tremendous loss of trabecular bone. This is noted on plain x-ray imaging studies, but dual-energy x-ray absorptiometry may show a paradoxical increase in density as a result of enthesopathy and greater peripheral bone formation.³⁸

Primary Management

Nonsteroidal anti-inflammatory drugs (NSAIDs) are used extensively for inflammatory and rheumatic disorders such as the spondyloarthropathies.³⁹ Recent evidence suggests that NSAIDs not only treat the symptoms of inflammatory polyarthropathy but may also have more of a “disease-modifying” role by retarding radiographic progression and symptoms of arthritis.⁴⁰ Celecoxib, indomethacin, naproxen, and phenylbutazone are among such medications that have specifically been used for the treatment of AS.⁴¹^–⁴⁴ To avoid complications associated with long-term use, medication use may be decreased during periods of relative disease inactivity.

Muscle relaxants may be used in conjunction with other drugs to ease the muscle spasms that accompany the spinal disease. Narcotic analgesics and oral corticosteroids are used only occasionally.

Disease-modifying antirheumatic drugs (DMARDs) have opened up a new avenue for treatment, and work continues to be done in the pharmacology arena.⁴⁵ There are several regularly used drugs that have various mechanisms of action. Sulfasalazine and methotrexate have a history of effective use in patients with rheumatoid arthritis and are used for treatment of the spondyloarthropathies as well. Nevertheless, their efficacy in treating axial spinal pathology such as seen in the spondyloarthropathies is relatively limited.^46,⁴⁷

Other DMARDs include adalimumab, etanercept, and infliximab. These drugs are examples of TNF-α inhibitors ⁴⁸^–⁵⁰ and are recombinant TNF-α receptors that bind the molecule in serum, thereby preventing systemic activity.⁵¹ They have been found to exert a beneficial effect on articular cartilage inasmuch as a decrease in serum markers of cartilage degradation has been observed.⁵² Intra-articular injection of anti-TNF agents has also been described.⁵³ These agents may be used in combination with other medications, such as methotrexate. However, the risk for serious infection increases significantly with such therapy. Widespread use of these drugs is limited somewhat by cost^54,⁵⁵ and concerns regarding long-term use.^56,⁵⁷

The response to treatment with drugs may be monitored by following serum levels of acute-phase reactants such as the erythrocyte sedimentation rate, C-reactive protein, MMP-3,⁵⁸ and various cytokines.^59,⁶⁰ Serum markers of bone and cartilage degradation and synthesis are also useful in this manner and are thought to be related not only to cartilage and collagen turnover but also to new bone formation through endochondral ossification, as occurs in the spine of patients with AS.⁶¹

In the case of psoriatic arthritis, TNF-α antagonists are used for both skin and joint disease, whereas efalizumab, which targets T lymphocytes, is indicated only for the skin disease.⁶²^–⁶⁵

Reactive arthritis is relatively unique in its relationship with infection, and although antibiotics have been used to battle the associated predisposing infections, the degree to which these drugs target the arthropathy is unclear.

Exercise therapy is considered helpful in maintaining patient function, and there is evidence of a direct biologic effect of such therapy. Patients who regularly perform back exercises and have appropriate social support have been shown to have a greater degree of function.⁶⁶ Exercises focus on strengthening of the spinal extensor muscles and maintenance of peripheral joint mobility. However, there is a need for a standardized approach to complement medical therapy.⁶⁷

Tobacco abuse is also associated with poor function.⁵³ Discontinuation of tobacco and nicotine products is thus critical not only for surgical patients but also for improved disease management in any patient with AS.

The response to treatment and resulting function may be monitored objectively with use of the Bath Ankylosing Spondylitis Functional Index (BASFI). This index provides patients a score from 0 to 100, with higher scores indicating greater disability.

Trauma Management

It has long been recognized that ankylosing spondylitis places a patient at higher risk for spinal fractures, even with minimal trauma.⁶⁸^–⁷⁰ The ossified, nonpliable spine is prone to failure, and the spine acts as a single long bone with high forces of moment at either end of the fracture. Associated osteopenia further predisposes the patient to injury. Patients are at risk for multiple fractures on repeated occasions.⁷¹

In the trauma setting, it is important to place patients close to their preinjury alignment rather than a normal neutral one. This typically requires building pillows behind their neck and thoracic spine and even elevating the head of the bed for a thoracolumbar injury.^72,⁷³ Patients may self-osteotomize after a fracture and fall into a deceptively normal alignment. This is at the peril of the underlying neurological elements, which are acutely angulated at the fracture site (Fig. 281-5).

FIGURE 281-5 Patients with ankylosing spondylitis and diffuse idiopathic skeletal hyperostosis are at risk for fractures with devastating consequences. This is the sagittal computed tomography scan of a patient who fell from standing height with resultant American Spinal Injury Association type A (ASIA-A) paraplegia.

The burden of a minimal fracture is far greater in a patient with AS because the spine tips into a kyphotic posture at the level of injury. Late deformity may thus occur with minimal trauma. Patients at times have a history of remote minor injury and worsening pain. A change in a patient’s pain, by and of itself, is an indication for investigation.

Subtle fractures may be missed either through a lack of appropriate suspicion for injury or through inadequate imaging studies. CT should be performed to rule out minimal fractures that would be missed on plain radiography.^74,⁷⁵ MRI can be of benefit in detecting subtle fracture patterns.⁷⁶ Flexible multipurpose coils help in positioning patients unable to fit in standard coils because of deformity.

The spectrum of injuries ranges from three-column extension injuries, in which the bamboo spine essentially snaps, to relatively innocuous-appearing anterior vertebral end-plate lesions. Fractures are most common in the cervical spine.⁷⁷ Healing of cervical fractures can occur reliably with the use of a halo vest in the absence of a globally destabilizing three-column injury. Surgery is indicated for unstable injuries demonstrating 360-degree instability and distraction, frequently at the thoracolumbar level. Epidural hematoma formation is common and must be evaluated with MRI in the event of neurological injury or deterioration.^78,⁷⁹ The integrity of a fourth column involving the costovertebral joint complex is a factor in the stability of thoracic-level fractures.⁸⁰

These injuries commonly involve an extension mechanism with an anterior “fish-mouthing” deformity that is amenable to anterior stabilization and closure of the fracture site. However, a high rate of failure has been noted with isolated anterior procedures, and therefore circumferential surgical stabilization of cervical injuries is often performed.⁸¹^–⁸³ Isolated posterior treatment can be effective.⁸⁴^–⁸⁶ Controversy exists with respect to restoring the patient’s preoperative alignment versus fixing the spine in a somewhat improved alignment in the acute setting.

Surgical Management

Indications

The main indication for surgery in a nontrauma situation is sagittal plane deformity. Some degree of coronal imbalance may occur and requires attention. Patients have fixed sagittal imbalance and complaints of difficulty maintaining forward gaze, especially while going up stairs. The back pain is aggravated by posture, and muscular spasm is common. Upper cervical instability and spondylodiskitis are other conditions that may require surgical treatment.

Preoperative Evaluation

A comprehensive discussion is undertaken with patients preoperatively regarding the precise nature of their disability, their occupation and hobbies, and expectations for not only postoperative alignment but also function. Some patients with cervical deformities prefer fusion in mild flexion if their daily activities require such a position.

A stepwise, systematic approach to these patients is mandatory and includes assessment of their imbalance clinically. Various postural tests can help in identifying the level of maximal deformity, including observation of the spine’s curvature in the standing, seated, and supine positions.⁸⁷

While the patient is standing, the deformity is typically at its worst. While seated, a hip flexion contracture is taken out of the equation, and if the majority of the deformity improves, it is evident that the hips require attention rather than the spine or that the hips should at least be addressed first. Once the hips have been addressed, any residual deformity attributable to the spine may then be addressed in stepwise fashion.

Next, the patient is moved from the seated to the supine position. If the deformity is corrected, it is attributed to the thoracolumbar spine.

Finally, if the deformity is maintained in the supine position, the curvature is attributed to the cervical spine or the cervicothoracic junction.

Preoperative Planning

Comprehensive evaluation of extraskeletal involvement is essential because multiple organ systems are directly affected by the disease. Attention is directed to associated cardiac, pulmonary, and renal dysfunction, as discussed previously.

Preoperative nutritional assessment, with measurement of serum prealbumin, albumin, and protein malnutrition, can be of benefit in anticipating the need for supplementary hyperalimentation or peripheral nutrition. Some evidence suggests that most if not all such patients benefit from postoperative nutritional supplementation. Some degree of dysphagia occurs after cervical osteotomy and can further interfere with nutrition.

Consideration may be given to staged surgery, whether combined anterior-posterior or posterior-alone intervention is planned.⁸⁸

Radiographic evaluation includes assessment of full-length standing anteroposterior and lateral radiographs of the entire spine. Anteroposterior radiographs are often difficult to interpret because of the flexion deformity. Angulation of the x-ray beam from caudad to cephalad may allow better visualization. The C7 coronal and sagittal plumb lines are assessed, and the deformity is measured in centimeters from these lines. Normally, the coronal plumb line is measured from the spinous process of C7 and should fall in the midline of the sacrum and symphysis pubis. The sagittal plumb line, measured from the center of the C7 body, normally descends to the posterosuperior corner of S1. Cervical and lumbar lordosis and thoracic kyphosis are measured by the Cobb method.⁸⁹ The sacral slope, inclination, and pelvic incidence is measured. Finally, the chin-brow vertical angle is measured.^90,⁹¹

The chin-brow vertical angle has been of great utility in assessing the degree of sagittal imbalance and in correlating it with the degree of bone resection required for surgical correction.⁹² This angle is measured on standing lateral radiographs and clinical photographs of the patient to provide direct measurement of the deformity and assessment of the correction needed to restore forward gaze.

Various techniques have been used for measuring the degree of deformity and correlating it with the degree of correction required.⁹³ Van Royen and colleagues devised a mathematical equation that factors in the variables of the degree of kyphosis and the correction needed and the level of osteotomy. A computer program is offered that may be used via the Internet.⁹⁴

The whole-body kyphosis angle, measured on clinical photographs with the patient in the standing position, has also been used.⁹⁵

Approaches

Opening Wedge Osteotomy

An opening wedge osteotomy involves resection of the posterior bony elements with subsequent hinging of the osteotomy at the posterior vertebral body and PLL level. This results in distraction, or opening, of the anterior column as the deformity is corrected (Fig. 281-6).

FIGURE 281-6 Opening wedge osteotomy.

Closing Wedge Osteotomy

Closing wedge osteotomies involve greater resection of the posterior elements with extension through the pedicles into the vertebral body. Closure is performed while hinging on the anterior body and anterior longitudinal ligament to avoid distraction of the anterior vascular structures and allow direct bone apposition for improved healing (Fig. 281-7).

FIGURE 281-7 Closing wedge osteotomy.

Closing wedge osteotomies are often performed at the thoracolumbar junction and opening wedge osteotomies at the cervicothoracic level.⁹⁶ However, both techniques have been used with favorable results at all levels of the spine, as will be discussed further.

Cervical Osteotomy

Simmons and colleagues described a 36-year experience with posterior opening wedge osteotomies.⁹⁷ Surgery is performed with the patient in the upright position under local anesthesia without instrumentation and involves an opening wedge osteotomy through C7 with varying degrees of pedicle resection. Excellent results have been achieved with this technique (Figs. 281-8 and 281-9). Closing wedge osteotomies have been used through the C7 pedicle with success as well.⁹⁸

FIGURE 281-8 A and B, Preoperative and postoperative clinical photographs of a patient with a fixed cervicothoracic kyphosis.

FIGURE 281-9 A and B, Intraoperative photographs demonstrating an opening wedge osteotomy through C7, before and after closure of the osteotomy, performed without instrumentation and with the patient in the seated position.

Etame and associates reviewed the literature related to osteotomy of the cervical spine in patients with AS.⁹⁹ Complications occurred frequently in six retrospective series, with rates ranging from 27% to 88%, but the major complication rate was relatively low, with a 2.6% mortality rate and a 4.3% rate of permanent neurological injury. Restoration of horizontal gaze was the norm and overall satisfaction was high.

Use of instrumentation in such cervical osteotomies has become more common, as has its use in spinal procedures in general. The advantages of instrumentation include limited need for postoperative bracing and relatively controlled motion during the osteoclasis portion of the osteotomy to prevent translational subluxation. The use of a hinged rod has been proposed to allow even further control of such translational force. The rod is temporarily fixed to screws with the hinge open at the osteotomy site, and then the hinge is locked once the desired reduction is achieved.¹⁰⁰

Disadvantages of the use of instrumentation include the need for more extensive cephalocaudad dissection for the placement of screws and the associated increased operative time and potential risk for infection. A further disadvantage with the use of internal fixation includes the lack of ability to adjust a patient’s alignment postoperatively, such as could be performed with relative ease by adjustment of a halo orthosis.

Thoracic Osteotomy

Smith-Petersen–type multilevel posterior osteotomies tend to be the mainstay of treatment of deformities addressed at the thoracic level. These osteotomies are attempted without lengthening of the anterior column, thereby decreasing the risk for anterior vascular injury and pseudarthrosis through the gap in the anterior column associated with an opening wedge osteotomy. Limited correction is obtained with this approach, especially in patients with complete ankylosis of the anterior column.

Primary thoracic curves may be treated by either thoracic or lumbar osteotomy. Lumbar osteotomy is often preferable because it avoids the thoracic spinal cord and rib cage and provides a long lever arm for correction. A single-level lumbar closing wedge osteotomy thus offers significant advantages over multiple thoracic Smith-Petersen osteotomies.

Lumbar Osteotomy

Heinig and McMaster each described a method for correction of deformity in which increased bone apposition is achieved by decancellation of the pedicle and vertebral body.¹⁰¹ Terms such as eggshell osteotomy, pedicle subtraction osteotomy, and closing wedge osteotomy describe similar procedures, and authors may vary in their description of the amount and technique of bone resection. Variations involving the extent of decompressive laminectomy and actual fracture of the anterior vertebral margin have been described (Figs. 281-10 and 281-11).¹⁰²

FIGURE 281-10 A and B, Preoperative and postoperative clinical photographs of a patient with fixed thoracolumbar kyphosis.

FIGURE 281-11 A and B, Preoperative and postoperative radiographs of a patient with fixed thoracolumbar kyphosis.

Combinations of closing and opening wedge osteotomies have been proposed for greater correction.^7,¹⁰³ When using such techniques, the first 30 degrees of correction is achieved with a closing osteotomy hinged at the anterior longitudinal ligament, followed by an additional 10 degrees by moving the hinge posterior.

Interbody cages have also been used for simultaneous closing/opening osteotomies and may afford greater support of the anterior column and decrease sagittal translation in selected cases.¹⁰⁴

Sagittal translation at the level of osteotomy may occur with either the open or closed wedge techniques. Although such translation has been thought to afford greater correction, it is associated with higher rates of neurological injury.¹⁰⁵

Various strategies for controlled osteotomy closure with instrumentation have been proposed, including placement of a central compression hook-rod construct through which the osteotomies are closed first, followed by secondary locking of the main pedicle screw-rod construct. This technique has been proposed to allow less direct transmission of force to the final construct itself. Meticulous attention to bone grafting and the surface area for fusion would be warranted with the placement of extra instrumentation over the planned area for fusion.¹⁰⁶ Methods have been proposed for more controlled osteoclasis, such as placing the operating table in the prone position.¹⁰⁷

Areas of pseudarthrosis within the otherwise ankylosed spine may take on a destructive appearance and be associated with considerable deformity.^108,¹⁰⁹ Opening wedge osteotomies with anterior interbody fusion have been used at the level of pseudarthrosis. In Kim and coworkers’ series, lumbar closing wedge osteotomies were also performed for further correction of severe deformities.¹⁰⁸ Chang and colleagues reported performing posterior osteotomies in a series of 30 patients without concomitant anterior interbody fusion and noted no failure of treatment after nearly 5 years.

Several authors have reported their series of patients with overall favorable results.¹¹⁰

Chen and associates described their series of 78 patients in whom closing wedge osteotomies were performed. Good or excellent outcomes were reported in 98% of the patients, with an average correction of 34 degrees per osteotomy level, typically at L2 or L3. Severe deformity was treated with multilevel osteotomies in a staged fashion, although in one instance, 100-degree correction was obtained at a single level. No severe neurological deficits or deaths occurred.¹¹¹

Weale and coauthors described their series of 50 patients. Instrumentation failures were noted with both transpedicular and other forms of fixation, but greater maintenance of correction was achieved with transpedicular constructs. A mean correction of 38 degrees was reported with two deaths and one sacral root injury.¹¹²

Kim and collaborators described a prospective series of 45 patients treated with closing wedge osteotomies.¹¹³ In their series, radiographic correction did not correlate with clinical outcome.

Chang and coauthors reported their experience with opening and closing wedge techniques.¹¹⁴ Correction was achieved with both techniques, and although closing osteotomies resulted in higher blood loss, a lower rate of postoperative ileus and delayed union with instrumentation failure was noted.

Combined Anterior and Posterior Approaches

Anterior-posterior procedures are less frequently used for the management of deformity. Mummaneni and colleagues described an anterior-posterior-anterior approach to the cervical spine.¹¹⁵ Placement of structural bone graft and cages has been advocated for anterior column support to prevent pseudarthrosis after an opening wedge lumbar osteotomy.¹¹⁶ Combined approaches are useful in treating complex multiplanar deformities with both coronal and sagittal components. Resection of the vertebral column may be performed in this manner to allow greater control of correction.^117,¹¹⁸