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Fractures in Spinal Ankylosing Disorders: A Narrative Review of Disease and Injury Types, Treatment Techniques, and Outcomes

Rustagi, Tarush MD*; Drazin, Doniel MD, MA*; Oner, Cumhur MD, PhD; York, Jonathan MD; Schroeder, Gregory D. MD§; Vaccaro, Alexander R. MD, PhD, MBA§; Oskouian, Rod J. MD*; Chapman, Jens R. MD*

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Journal of Orthopaedic Trauma: September 2017 - Volume 31 - Issue - p S57-S74
doi: 10.1097/BOT.0000000000000953
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Abstract

INTRODUCTION

Spinal columns afflicted with spinal ankylosing disorders (SADs) continue to pose a challenge for patients and practitioners alike. The presence of such disorders continues to be underappreciated. This leads to general unawareness of the disease state, its potential impact on patients, and results in common delays in diagnosis following often trivial injuries on the part of physicians. Aside from diagnostic uncertainties, treatment choices remain less than clear because of a variety of circumstances. This, in conjunction with changing population demographics and generally reported poor outcomes, renders injuries of ankylosing spinal columns to be one of the current most feared clinical entities in spinal trauma care. The 3 major entities that constitute SADs are ankylosing spondylitis (AS), disseminated idiopathic skeletal hyperostosis (DISH), and “end-stage advanced spondylosis multiforme” (EASM). Understanding of these disease entities in their idiosyncrasies and their clinical impact on diagnosis, treatment across multiple medical specialties would seem important to try to improve the currently published relatively poor outcomes for patients. It is the intent of this study to raise disease awareness among practitioners relative to SAD, including primary care physicians, rheumatologists, emergency department physicians as well as organized first responders, radiologists, spine physicians, and surgeons by providing a recent survey of publications surrounding diagnosis and care.

ANKYLOSING SPONDYLITIS (AS)

Etiology

Ankylosing spondylitis (AS), also known as Bechterew disease, is a relatively well-described subtype of a seronegative spondyloarthropathy. This group includes traditional AS, psoriatic arthritis, reactive arthritis, arthritis associated with inflammatory bowel disease, and undifferentiated types.1 The incidence of AS has been reported to be between 0.5 and 14 per 100,000 people per year. The prevalence is between 0.1% and 1.4% with men affected twice as often as women.2–4 A few studies have suggested a possible equal sex distribution of the disease because of underreporting of the milder forms, which affect women.3 The disease is more prevalent in North European countries and least likely to be found in individuals of Afro-Caribbean descent.5 A high prevalence of AS has been found in China and Turkey. AS has an onset before the age of 30 years in 80% of cases.6

The common genetic factor among spondyloarthropathies is the HLA B27 complex. Only 5% of patients with a positive HLA-B27 test result develop AS, but 95% of diagnosed AS cases have tested positive for HLA-B27.1,4,7 Therefore, routine HLA-B27 testing is no longer required to establish a diagnosis in patients with radiographically clearly manifest AS disease. Other genetic and environmental factors may be contributing to the occurrence of AS. For example, 15%–20% cases have a positive family history of the disease.1 Some evidence has shown that Klebsiella pneumoniae may initiate the disease process in patients who are HLA-B27 positive.1 The disease often progresses slowly starting from the sacroiliac (SI) joints and moving rostrally but can also start and progress away from the SI joints. The complication of vertebral fractures is usually seen slightly later in life when the disease has advanced in severity.8

Clinical Manifestations

Although first formally classified in 1984 and with the Modified New York Criteria used to establish the diagnosis, medical professionals of all specialties remain not very effective in identifying early disease or differentiating it from other ankylosing spine disorders.7 Key hallmarks of AS are the presence of ossification of the ligaments (enthesopathy). The ossification process involves the disk, endplates, and apophyseal structures resulting in remodeling of the vertebra giving a classical appearance of a bamboo spine (squared vertebra).9,10 Osteoporosis is strongly associated with AS and is one of the important factors in the evolution of spontaneous vertebral fractures and poses problems in surgery. The ectopic bone is formed in the areas of ongoing inflammation with high osteoclastic activity resulting in poor mineralization of the bone. The presence of syndesmophytes results in high false positive rates of measuring BMD using conventional DEXA scans.11–13

A confusing finding in AS can be skip lesions, likely focal nonunions in the midst of an otherwise fully fused spine. These may be interpreted as “sterile spondylodiscitis” or seen as a fracture, but most likely it simply represents a nonfused motion segment in the midst of a long bone type frozen spinal column.14–17 Other important variables which differentiate AS from other SADs are the presence of kyphotic deformity, ankylosis of the craniocervical junction, and ankylosis of costovertebral joints.18–20 All these have significant repercussions on patient outcomes and management. For patients with deformity, the question of emergency retrieval and optimal stabilization with or without deformity reduction remains controversial. Patients without movement of their craniocervical junction require especially complex considerations in their treatment. Ankylosis of costovertebral articulations is another AS-specific hallmark and results in chest wall rigidity, a restrictive ventilator defect, and a high susceptibility to pulmonary deterioration.21,22 The most common manifestation of the restrictive defect is a reduction in total lung capacity, vital capacity, low forced vital capacity, and low forced expiratory flow in 1 second (FEV1). Because of the reduced chest wall mobility in AS, there is an increased contribution of the diaphragm and abdominal muscles to compensate.21

DISSEMINATED IDIOPATHIC SKELETAL HYPEROSTOSIS (DISH)

Epidemiology and Clinical Manifestations

Disseminated idiopathic skeletal hyperostosis (DISH), also known as ankylosing hyperostosis or Forestier disease has become increasingly well recognized as a major variant of SAD distinct from AS by virtue of the type of patients affected and important radiographic and other clinical differences.23,24 Some important disease manifestations have been formulated to include male preponderance, more advanced age, and coincidence with a clinical trifecta of comorbidities including pulmonary hypertension, neuropathy inducing end organ diseases such as diabetes, elevated systemic inflammatory proteins, and advanced obesity.25 The typical disease manifestation involves the thoracic spine, where typically more than 3 adjacent segments are coalesced in a hypertrophic exophytic bony overgrowth usually seen anterior to the spinal column.26 Ossification in DISH occurs essentially in the anterior longitudinal ligament (ALL) and minimally involves the paravertebral connective tissue.27 The process of ossification may involve more than 1 spinal region. Most common areas of involvement are the middle and lower part of the thoracic spine (T7-11), often in isolation.24,26,28,29 The ossification of the ALL extends laterally along the ALL. In the thoracic spine, the anterolateral ossification is more prominent on the right side. Pulsation of the descending aorta limits bone formation on the left side.30,31 The lumbar spine is involved next most commonly after thoracic spine followed by cervical spine.23,24 Pain and stiffness is the most common association in spine. Extension of ossification process involving the ligamentum flavum in the lumbar spine and posterior longitudinal ligament in the cervicothoracic spine results in spinal stenosis.32–34 Dysphagia has been found on average in 28% of DISH cases involving the cervical spine.34–38 Other associations in the cervical spine include hoarseness of voice, sleep apnea, and difficult intubation.34,39,40

The cause of DISH remains largely unknown.34,41–43 Attempts to find association between DISH and HLA-B27 have been inconclusive.24 Endocrine and metabolic disorders, such as diabetes, acromegaly, hypervitaminosis A, hyperuricemia, and dyslipidemia have been found.44 HLA-B8 has been found to be associated with diabetes and DISH.34

The diagnostic criterion for DISH was laid down by Forestier and modified by Resnick and Niwayama.26 The key radiologic difference between DISH and AS lies in the absence of involvement of SI and apophyseal joints in DISH and absence of involvement of the craniocervical joints. Also, there is no syndesmophyte formation in DISH.

Patients with DISH are not commonly affected by major spinal deformities, they tend to be older and the disease has a male preponderance. The typical comorbidities of affected patients include pulmonary hypertension, metabolic diseases such as diabetes mellitus (often poorly controlled), abdominal adiposity, and an elevated baseline C-reactive protein (metabolic syndrome). Important considerations clinically are the involvement of the thoracic spine, which can offer radiographic hints of its presence on plain radiography or computed tomography (CT), but is usually only marginally visualized on diagnostic tests of the cervical and lumbar spines.

From a clinical perspective, patients with DISH are at risk from acute or subacute loss of neurologic function because of high-grade spinal stenosis.45 The neurologic deficit may manifest itself without significant trauma and may have a surreptitious course.

END-STAGE ADVANCED SPONDYLOSIS MULTIFORME (EASM)

Epidemiology and Genetics

This variant of SAD has been postulated as an alternative variant to AS and DISH because of its difference in etiology. Although the latter clearly has a serologic or inflammatory pathway at its onset, EASM may have a number of other factors at its core, such as metabolic and endocrine conditions, including hypervitaminosis A/D and psoriasis.42,46–49 Certain animal studies have also found associations between high vitamin A levels and deformed cervical spine.

Other etiologies in this group include inflammatory diffuse hypertrophic osteoarthropathies and advanced degenerative spondylosis from age-related facet arthritis and collapse of the intervertebral disk space. Because spondylosis mainly occurs in the mobile spine, this entity is usually seen in the cervical and in the lumbar spine. Dagi et al described patients with diffuse hypertrophic osteoarthritis that present with tandem stenosis involving cervical and the lumbar spine.50

In contrast to the previous 2 disease states, these patients usually do not attain osseous ankylosis. They may, however, be disproportionally affected by spinal stenosis. In contrast to AS, the spinal column in EASM is usually highly osteodense with sclerotic processes visible along its articulations. Spinal deformity is not a common occurrence, but highly dystrophic facet joints and osteophytes can make injury recognition and treatment very challenging.50

Another emerging SAD entity is surgically fused spines, especially with multilevel fusions, these patients are more susceptible to fractures at levels adjacent to the fused segments. The context of this narrative review does not allow further review of this subentity.

METHODS

Literature Review

PubMed and MEDLINE databases were both searched to identify articles published between 2001 and 2016 pertinent to the methods and outcomes of surgical treatment of the ankylosing spine.

The key words used in the search were “ankylosing spondylitis,” “DISH,” “ankylosing spine,” “fracture,” “treatment,” “outcome,” and/or “epidemiology.” Inclusion criteria were full-length English-language articles or abstracts, prospective studies, and retrospective studies. Exclusion criteria were articles or abstracts with inadequate information about outcomes and/or surgical treatment.

An initial search using the key words “ankylosing,” “spine,” and/or “fracture” returned 559 articles. The search was further limited by date (2001–2016) and to the English-language literature (264 articles). Two separate authors (D.D. and J.Y.) reviewed abstracts from these articles.

Of these 264 articles, 243 were excluded from analysis because they failed to meet the surgical treatment criterion or to report postoperative outcomes, or were case reports and case series with fewer than 10 patients. The remaining 21 articles were included in our analysis. Articles were reviewed for data on methodology (retrospective vs. prospective), type of treatment, number of patients, mean patient age, and mean follow-up. Specifics on the patient and the fracture included which level of fracture, complications, and need for reoperation. Clinical outcome data were also recorded when available.

General Overview

Twenty-one major studies published between 2001 and 2016 were identified in the literature that studied ankylosing spinal disorders (Table 1). Retrospective cohort studies formed the preponderance of the body of research. The remainder included 1 case–control study, 2 prospective cohorts, and 1 meta-analysis. Twelve studies included fractures from all regions of the spine. Five studies focused only on cervical fractures, and 3 focused on management of traumatic thoracolumbar fractures. The average patient age at the time of injury was 63.4 years, and most patients were men (range 65%–100%). The most common comorbidities were hypertension, coronary artery disease, diabetes, and pulmonary disease. Ground level falls or low energy trauma was the most common mechanisms of injury. When specified in the study, a delay in diagnosis was seen in 15%–41% of patients. Hyperextension fracture patterns were most common. In studies that reported concurrent epidural hematoma, the range was 7%–23%.

T1
TABLE 1.:
Evidence Table for Publications on SAD Fractures Used in Our Systematic Review
table1-a
TABLE 1-A.:
Evidence Table for Publications on SAD Fractures Used in Our Systematic Review
table1-b
TABLE 1-B.:
Evidence Table for Publications on SAD Fractures Used in Our Systematic Review
table1-c
TABLE 1-C.:
Evidence Table for Publications on SAD Fractures Used in Our Systematic Review
table1-d
TABLE 1-D.:
Evidence Table for Publications on SAD Fractures Used in Our Systematic Review
table1-e
TABLE 1-E.:
Evidence Table for Publications on SAD Fractures Used in Our Systematic Review

In most studies, cervical spine fractures were more common than thoracolumbar fractures, with C5-7 being the most frequently described sites of injury. At the time of presentation to surgeons, neurologic deficits were seen between 21% and 100% of patients. Operative stabilization and fusion were performed in 40%–100% of patients. Mortality ranged from 0% to 32% at 1-year postinjury. Complications were seen in up to 84% of patients. Pneumonia, respiratory failure, and pseudoarthrosis were most frequently described. Neurologic deterioration from initial examination, either pre- or postoperatively, was noted in up to 16% of patients. Fusion was obtained ultimately in 87%–100% of patients. Patients with neurologic deficits demonstrated improvement in neurologic function at follow-up in 6%–66% of cases.

Spine Fracture Variables

Individuals with advanced SAD commonly have impaired mobility because of spinal deformities and peripheral joint arthritis that make them more susceptible to falls, secondary to gait abnormality. Studies have suggested that people with AS are at a higher risk of falls than control groups.34,44,51–55 Low-impact ground level falls have been associated with spine fractures in patients with SAD in 65.8%, whereas high-energy impact has been found in 31% of patients.55,56 Progressive remodeling of the vertebral column with poor muscle tone results in fixed kyphotic deformities especially in patients with AS. The positive sagittal alignment itself poses a risk factor for fractures.19,51,57,58,59

Aside from fracture location(s) and geographic distribution of SAD, presence of severe osteoporosis in concurrence with an underlying inflammatory disease process creates a higher likelihood for fractures from trivial trauma.34,55,56 The weakened bone quality and adverse alignment is also a risk factor for higher failure rates of fixation of spine implants.60

Unusual injury presentations, such as spontaneous atlanto-occipital subluxation and atlanto-axial subluxation may also affect the craniovertebral (CV) junction, especially in the presence of fusion of the subaxial spine in patients with AS. Pathogenetic factors leading to such subluxation include formation of a retrodental pannus secondary to chronic instability, de novo involvement of the transverse and other CV ligaments by the disease process itself, and bony erosion by the disease process resulting in CV junction subluxation.25,61,62 In a review of risk factors for spine fracture in AS, Geusens et al found men to be twice more often affected than women, and further fracture risk factors to be elevated with low body mass index, disease duration, degrees of syndesmophyte formation, restriction of spine movement, and kyphosis (measure by occiput-wall distance) among them.56

Fracture Incidence/Distribution/Mechanism

Incidence of spine fracture with AS is higher than normal. Cooper et al found that the odds ratio is 7.7 for sustaining a spine fracture in the presence of AS compared with the general population; the cumulative incidence is 17%, 30 years after the AS diagnosis has been established.52 The risk of incurring a spine fracture after injury in AS grows gradually with time. Forty-five years after an AS diagnosis, the risk of sustaining a vertebral fracture is an added 1.3% per year.52

In a retrospective cohort study looking at patients admitted to hospitals in the United States between 2005 and 2011 with a diagnosis of fracture and AS in the National Inpatient Sample database, Lukasiewicz et al compared and analyzed 939 patients. They found that 85% of cases were men and most fractures occurred after 70 years of age, with <0.4% below 30 years and 51.7% after 70 years. The distribution of fracture was 53% in the cervical spine, 41.9% thoracic, 18.2% lumbar, and 1.5% sacrum. Spinal cord injury (SCI) was seen in 21.1% of patients most commonly in the cervical spine (14.6%), followed by thoracic spine (6.7%). Multiple and frequently noncontiguous fractures were seen in 13.1% of cases with the majority being a combination of cervical and thoracic (6.5%), followed by thoracic and lumbar (4.3%), cervical and thoracic (1.3%), and 1.1% involving all areas of the spine.63 Altenbernd et al reported an 8% incidence of multilevel fractures in patients with AS.58 In a systematic review looking at 280 cases of AS with spine fractures, Westerveld found cervical fractures accounted for 81.2%, thoracic spine (10.7%), and lumbar spine (7.8%).64 Other studies further reinforced the notion that the lower cervical spine is the most common spine region to sustain a fracture, followed by the thoracolumbar spine.27,65,66 Most fractures in the cervical spine involve the cervicothoracic transition zone, which is difficult to visualize on conventional radiography.27,50,66–70

Extension type injuries are the most common mechanism of fracture, irrespective of the area of spine. In a systematic review, Westerveld et al looked at fracture types, pattern, and neurologic findings.64 They found that 74.4% of injuries in AS were extension injury, followed by flexion injury (20%), rotational (5.4%), and compression (4.7%). They found some differences in the mechanism of injury in DISH with over half sustaining an extension injury (51.5% extension, 34.9% rotation, and 14% compression and no flexion injury).64

The fracture line in DISH typically passes through the vertebral body in the majority of the cases in contrast to AS where it passes through the former disk space.71 This is probably because a calcified disk is the weakest link in the otherwise stiff spine of AS, secondary to chondroid metaplasia.72

Andersson lesions are not an uncommon finding in the later stage of AS. They are essentially vertebral or discovertebral processes that represent a nonunion of a spine fracture or incomplete consolidation.15,16,27,73 Various reasons were found to suggest formation of these lesions. These included repeated stress across an incompletely ossified bone.15 Biomechanical reasons including kyphosis and long level arm have been suggested for nonunion.15,67 Recognition of this entity is important as it may be accompanied by a secondary focal stenosis. It can also be misdiagnosed as an infection and certainly is of importance as to consideration in a treatment plan.

SCI is a feared and disastrous complication associated with spine fracture in SAD. A retrospective case review looking at patients with SCI found that 1.5%–2% had AS.74–76 Alaranta et al looked at the Finnish national prevalence data and found that the incidence of SCI in patients with AS was 11.4 times more than the normal population.74 Complete cord injuries were also seen more commonly in AS than in mobile spinal columns.70,74,76–78

Westerveld et al found that 67.2% of cases of spine fractures had neurologic deficit (ASIA A-D). They also found that secondary deterioration in the neurologic status was seen in 13.9% of patients.64 Suggestions for the reasons for this secondary deterioration included improper initial assessment, missing the diagnosis of fracture, improper transfer of patients with unstable spine, and epidural hematoma formation.64

Overall, the risk of incurring a new onset neurodeficit after a cervical injury in patients with AS is at least 3 times that of the general population.79 Sapkas et al reported that the risk of neurodeficit after a cervical fracture in AS was around 42%.80

Diagnosing Spine Fractures

Diagnosing spine fracture in patients with SAD is notoriously challenging because of a number of factors, including fracture location in transitions zones, highly dystrophic or misshapen bone, and body morphology and/or deformity. Given the fact that most patients with SAD have chronic pain, many patients may not even seek medical attention and are not aware of the potential adverse sequelae of a missed spine injury after a simple ground level fall or other low-impact events. Many authors recommend assuming that any SAD patient with an injury mechanism has a fracture after any trivial injury unless proven otherwise. Maintaining a high index of suspicion in such patients is important but necessitates previous recognition of the ankylosing disease process in the first place, something that remains challenging in practice.

Throughout the studies abstracted and reviewed, there were a persistent number of injuries that had been missed or where patients experienced a delay in diagnosis. In a study by Milicic et al, 42% of cases of AS with spine fractures did not get the correct diagnosis initially.81 Westerveld et al noted that in 17.1% of cases, the spinal fracture was not noticed within 24 hours after the injury. In half of these patients (52.5%), the delay was on the part of the treating physician, whereas in 47.6%, the patient did not report the injury or seek a medical opinion.82

Numerous reasons have been found for missing the diagnosis of the vertebral fracture. Most patients with AS, for example, have preexisting axial pain. Also, a trivial trauma may not seem severe enough to warrant evaluation by both the patient and the physician.83,84 Einseidel et al identified a phenomenon called “Fatal Pause,” wherein the patients did not identify the symptoms of a fracture until they started to develop neurologic symptoms.85

Radiographs in patients with SAD can be truly challenging to interpret for injuries. Most of the fracture/dislocations occur in transition zones of the spinal column, which is notoriously difficult to visualize on plain radiographs.71,74 Koivikko et al found that only 48% of fractures in the cervical spine could be determined on plain radiographs leading to their recommendation that screening CT or magnetic resonance imaging (MRI) of the entire spinal column in at-risk patients.86 Severe kyphotic and other deformities may, however, complicate obtaining or interpreting images. Clinically many patients with SAD are on anti-inflammatories or long-term opioids which may diminish some of the pain associated with these injuries.

There are a number of differential diagnoses which may obfuscate the detection of an injury. A relatively common example is an area of a focal nonunion of an ankylosing spine, such as Andersson lesion. Dave et al described 29 patients with focal nonunion of the spinal column (Andersson lesion), of which 10 were diagnosed as tuberculosis and started on anti-TB medication.14 Unfortunately, inflammatory markers are typically elevated in patients with AS and DISH, further aggravating differential diagnosis to an infectious process. De Ross et al suggested that absence of soft tissue swelling, paravertebral mass, or loss of fat planes on MRI may indicate a nonunion in the form of an Andersson lesion and help rule out injury or infection.87

In general, both CT and MRI have been recommended as the primary investigations of choice when possible to identify spinal injuries in patients with SAD. Koivikko et al found that MRI showed fractures in patients with AS only in 60% of cases and therefore recommended the use of adjuvant CT (90). They studied 20 patients, where MRI detected 2 fractures that were missed on CT and on reverse CT picked up 6 fractures that were missed on MRI. They recommended to use MRI and CT as complementary rather than alternate studies for patients with SAD. This was also reinforced by Whang et al to specifically identify injuries involving the posterior column that may be missed even with a CT.88

MRI will also allow identification of an epidural hematoma as a potential threat to neural structures that may go unnoticed on a CT.89,90 Multilevel involvement is an important concern that needs careful attention and consideration so as not to miss injuries. It is recommended that the entire spine be screened in AS patients with a suspected fracture.83,91,92

General Considerations in Treatment Selection: Nonsurgical Versus Operative

Management of spine fractures in SAD is complex from a number of perspectives. Most patients with SAD are older and suffer from multiple significant medical comorbidities. The altered biomechanics and alignment of the spine and the injury pattern make these injuries highly unstable. Even the simple act of recovering and transferring patients with SAD to a medical facility can be precarious as conventional recovery strategies with neck collars in supine positioning on a rigid backboard may cause secondary displacement and neurologic deterioration in patients with a broken ankylosed spine. Also in surgery, osteoporosis will impair implant purchase. Traditional anatomic and radiographic landmarks needed for safe implant placement may be distorted or flat-out absent. In addition, the bones and soft tissues in patients with SAD tend to bleed significantly and also can form an epidural hematoma.93,94

Medical problems commonly associated with AS specifically include cardiac conduction abnormalities, aortitis, valvular heart disease, impaired renal function from long-term NSAIDs, decreased pulmonary capacity, obesity, pleural thickening, and interstitial lung disease.1,8,10,22,55,84,95 Commonly encountered medical therapies can impact surgical timing and intraoperative burdens to the patient, such as anticoagulants, anti-inflammatories, and pulmonary constraints or hypertensions.

In a retrospective cohort study, Lukasiewicz et al looked at mortality, adverse events, and length of stay (LOS) for AS fractures relative to different spine regions and associated SCI.63 They found that mortality, adverse events, and LOS were seen more with associated SCI (RR 3.44 for mortality). The risk of mortality at 1 year has been reported as high as 32%.84 As compared to cervical fractures, mortality was seen significantly less in fractures in the thoracic region and was insignificant for lumbar spine. Adverse event and LOS were not found significantly different among different spine regions.63

Generally nonsurgical treatment of SAD spine fractures are rarely recommended for all but nondisplaced and clinically stable injuries. Secondary fracture displacement in injuries more unstable than anticipated and patient intolerance to bracing are common reasons for the reported high failure rate of nonsurgical treatment of almost 50% for patients with SAD fractures.92,96 In their meta-analysis, Westerveld et al reported that 46% of spine fractures in AS were treated conservatively with medical comorbidities being the leading selection criterion for this modality, showing that factors other than fracture care may dictate treatment selection.82 In a retrospective cohort study of 939 patients, Lukasiewicz et al found that 49.9% of patients ended up with instrumented fusion surgery.63 Sadly, there is an apparent selection bias that limits any attempt at comparing nonsurgical and operative SAD fracture care.

The most often cited reasons for surgical intervention include neurologic deterioration, presence of an “unstable fracture,” or detection of an epidural hematoma (Fig. 1). Whang et al compared the treatment options and outcomes in fractures involving patients with AS or DISH and reported good outcomes in 83% of the patients treated surgically.88 In a retrospective series of 75 patients with thoracolumbar fractures, Caron et al reported the mortality of nonsurgically treated patients at 1 year to be 51% compared with 32% in the surgical group.84 Lu et al reported solid fusion and reversal of neurologic deficit after surgical management in all patients of their retrospective case series.97 Westerveld further confirmed that surgical intervention in the presence of neurologic deficit resulted in no further decline in 59% of cases and improvement in 27% of cases.82

F1
FIGURE 1.:
Case 1: Sagittal CT images of a 60-year-old woman with DISH who sustained a hyperextension injury C5-6 after a ground level fall on her head. On the subsequent images, the skeletal injury was not appreciated and therefore not treated. The patient spontaneously developed sudden onset of quadriplegia, after impinging her spinal cord (sagittal MRI—panel C). She was then treated emergently with anterior decompression and fusion followed by posterior decompression and segmental instrumentation (D and E). She did make significant recovery (see case 1 description).

Numerous studies have shown the potential risks associated with nonsurgical SAD fracture management. Patients with AS are at a higher risk to develop pulmonary complications, thromboembolism, and decubitus ulcers with bed rest.60 Traction should be used very cautiously, if at all, for patients with SAD cervical fractures, because of the fear of neurologic decline than be incurred through uncontrolled translation of the fractured spinal column ends.75 If cervical traction is used in SAD for fracture reduction, it has been recommended to use not more than 5 pounds weight.98

Use of a halo vest assembly for cervical fractures is problematic for patients with SAD because of their commonly advanced age, cervicothoracic kyphosis, and absent compliance of the frozen chest wall, all leading to an increased risk of aspiration and pulmonary deterioration due to immobility of their chest wall.65,99,100 General complications of nonsurgical care include potential worsening of alignment, nonunion, neurologic decline, and loss of reduction.64,82,84,88,91,101 An established pseudoarthrosis or an Andersson lesion of the thoracolumbar spine has been found to not heal with bracing or other immobilization.67

Nonsurgical Options in Cervical Spine Fractures

Immobilization of the fracture is the cornerstone for nonsurgical SAD fracture management. For cervical spine injuries, a collar or halo-vest immobilization is most often used.72,102 An orthotic extension to the thoracic and even lumbar spine may be selected depending on the area of instability.

In the setting of a patient with a SAD-related fracture, the fitting of an orthosis almost invariably needs to be customized to the patient because of the underlying body habitus and preexisting deformity.88 As most injuries are of a hyperextension type, Broom et al suggested aiming for a slightly kyphotic position in a brace to avoid hyperextension and secondary neurologic deficit.77 Delayed fracture displacement can occur early on and is best addressed by close follow-up with raised awareness of all caregivers toward alignment changes and neurologic decline.88 One-third of the patients have been reported to require surgical intervention after a failed initial nonsurgical trial.64,82,88

At the craniovertebral junction, nonsurgical management with a rigid orthosis has been historically reported for select neurologically intact patients.61,103 Nonsurgical care may also be the treatment of choice in moribund patients with prohibitively high perioperative morbidity risks and very poor risk/benefit ratios. A clear discussion of choices and possible involvement with a Palliative Medicine Service may be a reasonable choice for such patients, whereas providing a modicum of comfort with some form of a soft orthotic.

Nonsurgical Options in Thoracic/Lumbar Spine Fractures

In the thoracic spine, immobilization with a brace is an option for patients with more stable injury patterns or very sick patients. As in the cervical spine, the brace usually requires individualized fitting to match the body morphology and may need to incorporate the deformity that may exist. There are some important considerations to be made relative to nonoperative thoracolumbar fracture care in SAD.

For displaced upper- and midthoracic SAD fractures, the chest wall will not serve as the “fourth column” of theoretical stability but due to its ossified costovertebral junctions will continuously move the fractured area with every breath.104 Together with the loss of abdominal trunk ventilation in the setting of brace immobilization, brace confinement may be intolerable to patients with SAD. Lumbar spine fractures, which are less common in SAD, are more difficult to immobilize in a brace due to cantileverage forces induced by the pelvis. Although this could theoretically be counteracted by including 1 leg or the pelvis in the orthosis, the resultant loss of patient mobility- and immobility-induced morbidities make this not a very practical modality for these already compromised patients.92 In general, nonsurgical options for thoracolumbar fractures are limited to use of more supportive rather than truly immobilizing devices because of concerns of further pulmonary compromise and ineffectiveness in actually stabilizing the fracture.105

Surgical Options

Subaxial Spine

Surgical management of subaxial spine fractures in the presence of ankylosing conditions is generally supported in the form of low-level evidence of case reports and case series.

Subaxial fractures in AS usually involve the anterior and posterior columns, which makes anterior alone fixation susceptible to failure in about half of the patients where it was used.106,107 The adverse constellation of commonly present osteoporosis, with its limited screw purchase, long lever arms caused by the underlying ankylosing disorders, and frequently present kyphosis anterior approach to the cervical spine have remained generally unpopular for anesthesiologists and surgeons alike. Indeed, Westerveld reported that only 15% of AS fracture cases were treated with anterior surgery alone.64 Evidence in favor of isolated anterior surgery in SAD is limited to a few case reports. Anterior-only fixation may work if the anterior plate and screw construct is long enough to minimize leverage induced by the long movement arms created by the adjacent spine segments. This concept was successfully used for 16 patients as reported by Kouyoumdjian et al.106

Posterior approaches seem to be the by far most commonly chosen surgical technique for stabilization of subaxial spine SAD type fractures. In their systematic review, Westerveld reported that 50% of patients were treated with a posterior approach alone.64 This trend is further underscored by various case reports.64,69,108,109 The main advantage of a posterior approach is the relative ease of surgical approach in the presence of concomitant deformities as well as ready access to multiple rostral and caudal additional fixation points to decrease the lever arm acting on the fractured segment and also permit some deformity correction, if such is desired and felt to be safe. Another consideration in favor of a posterior approach is the relative ease to achieve a multilevel decompression through a concurrent laminectomy in the presence of neurologic deficit or epidural hematoma. An anterior column gap which has opened up during fracture reduction may need not to be filled with a secondary anterior procedure if adequate multilevel purchase through a longer posterior fixation construct has been achieved.88,109 Such long constructs bypassing the fracture ideally encompass at least 3 to 4 segments of rostral and distal fixation. However, poor anatomic landmarks and radiographic visualization as well as a generally higher invasiveness of posterior open surgery are a concern for patients with SAD.

Combined anterior/posterior surgery was used in 25% of patients as reported by Westerveld.64 This most invasive approach provides by far the greatest construct stability. In cases of coincident deformity correction during fracture treatment, such combined procedures have received strong support in a number of studies out of concern for implant failure.82,83,92,109,110 Combining an anterior construct with a posterior fixation may speed up fusion and also act as a load-sharing device. Einsiedel et al shared their experience at 2 trauma centers and recommended combined anterior and posterior surgery (either single stage or in 2 stages) for subaxial cervical spine fractures in patients with AS after they noticed a 50% failure rate with anterior-only surgery.100

A specific concern for posterior approaches in AS patients with unstable cervical fractures and deformities is patient positioning. During the turning maneuvers, fracture displacement can readily occur even with exacting technique. Turning tables may not be suitable for such patients, and a formal multiperson turn aided by neurophysiologic monitoring and imaging may be preferable. An alternative consists of a more limited anterior approach with a plate fixation to provide a temporary buttress before turning to the prone position for the posterior surgery, as shown in our illustrative case (Fig. 1).

Kanter et al discussed a treatment algorithm for management of AS cervical spine injuries from a perspective of timing of surgical intervention and approach. The algorithm was based on neurologic deficit, alignment of the fracture, reduction using a light traction of less than 5 pounds, and presence of deformity. They used the algorithm in 13 cases and found 92% solid fusion and improvement in Nurick and MJOA scores.98 Deformity correction at the time of fracture management for patients affected by pronounced preexistent spinal deformities has also been studied on a limited basis.65,98,111 Here, the surgeons performed an anterior wedge osteotomy at the C7 level, and any fractures at that level were used to accomplish further kyphocorrection.98,111

Recommendations regarding the timing of fracture management have been based on the severity of neurologic injury. Kanter et al suggested that patients with complete cord injury or central cord injury be operated upon when they are physiologically stable. They further recommended that patients with incomplete spinal cord injuries receive their definitive surgical decompression and fusion within 24 hours.98

Craniovertebral Junction

Patients with CV fractures or dislocations are an especially challenging problem in patients with SAD. Because of unusual bony anatomy, injuries and dislocations in this region are frequently overlooked or misinterpreted. Neurologic injuries at this level can be more catastrophic or present in unusual neurologic findings. Ventral cord compression in patients with SAD has lead some to suggest an anterior transpharyngeal decompression. Albert et al in their series reported successful use of this technique in 5 of their 7 cases, who all suffered from neurologic deficits and mostly improved after surgery.112

In another historic series of 22 cases, Sharp treated most of their patients with posterior decompression and fusion (occipitocervical fusion with iliac crest graft) after a careful closed reduction using some traction. Overall, 13 cases were put in preoperative traction. Of the 7 cases with presurgical deficit, 1 received traction and plaster, 5 traction and posterior fusion, and 1 patient died. The authors reported almost complete neural recovery in all the surviving patients in this historic series.113

In general, posterior segmental stabilization after reduction of a displaced craniocervical junction in ankylosing disorders together with indirect reduction has become the prevalent form of treatment, whereas anterior transoral approaches have become less commonly used.

Thoracic and Lumbar Fractures

To date, SAD-related thoracic and lumbar spine fractures have been less commonly reported than in the cervical spine. In general, nonsurgical options are not very effective in the management of unstable injuries. A long posterior stabilizing surgery is typically recommended.80,96,114,115

The posterior approach is a more familiar approach for most spine surgeons and also provides multiple points of fixation, as well as decompression as needed, especially around the injury zone.84,114,116,117 In light of long leverage arms of multilevel fused spinal columns and poor bone quality in patients with AS, Werner et al suggested at least 3 levels above and below the fracture level for fixation.92 Technical challenges in posterior screw placement frequently arise out of lack of posterior bony landmarks in AS or severely distorted facet joints in DISH and EASM, large body habitus, and spinal deformity. Even fluoroscopy may be limited in its ability to guide a surgeon under some of these circumstances. Being resourceful using antero-posterior and oblique image-intensifier angulations can help, and under some select circumstances image guidance may be helpful to find important aids to safe implant placement. Blood loss in these cases may also be higher than usually expected in light of the inflammatory underlying pathology, cavernous cancellous bone structures, and comorbidities such as adiposity or therapeutic anticoagulation93 (Fig. 2).

F2
FIGURE 2.:
The sagittal CT and MRI in A and B show an unstable L1 hyperextension fracture from a ground level fall in a 78-year-old male. A multilevel posterior segmental instrumentation was performed (C) which enabled the patient to mobilize without brace (see case 2 for further details).

Positioning is a major consideration in thoracolumbar patients with SAD fracture as well. Most of the patients have some form of an underlying kyphotic alignment with an extension type injury. Attempts at placing a thoracolumbar fracture patient with SAD prone on a standard Jackson table may cause further uncontrolled extension of the spine through the injury zone, with concordant potential for secondary neurologic decline and even vascular disruption. Surgeons may want to consider placing such patients on a frame that allows for a controllable kyphosis such afforded by a Wilson-type frame.88

In light of complications such as blood loss and infections associated with open more extensive multisegmental instrumentation and fusion surgeries, more recently minimally invasive spine surgery has been reported as an option for long segment posterior fixation in thoracolumbar SAD fractures. Yeoh et al performed a retrospective review of 10 cases treated with percutaneous posterior fixation and described good functional outcomes with low complications associated with surgery.117

Secondary anterior surgery of thoracic or lumbar spine fracture in SAD is rarely required because of the strong propensity of these patients to form bone and heal fractures. However, the presence of a large anterior gap may benefit from secondary anterior column reconstruction with a structural graft or cage. In light of the general vulnerability of these patients, it may be beneficial to defer anterior surgery until the patient has recovered from their posterior surgery.

Deformity correction at the time of SAD thoracolumbar fracture surgery has been presented in a few studies.115 Adding an osteotomy at the time of fracture fixation may be a preferable option but is an extensive procedure in itself. Werner et al recommended not attempting a deformity correction in the presence of a fracture because of increased complications.92

Surgical decompression in a SAD-related fracture may be indicated in the presence of an epidural hematoma or in case of irreducible fracture displacement. An additional unique indication for surgical decompression may present with incidentally found severe stenosis, which may be found in patients with hyperostotic SAD.33

COMPLICATIONS

Literally, everyone of the case series reports on significant morbidity and mortality associated with surgical and nonsurgical treatments regardless of the treatment chosen.64,84,115,118,119 This raises the question if, similar to geriatric hip fractures, spine fractures in SAD may be a manifestation of a general physiologic end point of patients. It comes as no particular surprise that over 80% of these usually elderly patients have at least 1 major comorbidity, together with a structural disrupted spinal column experience complication rates of more than 50 (or much higher) and 1 year mortality of 20% or higher in more recent series. That said the survival of surgically treated patients seems to be significantly better than that of nonsurgically treated patients in a larger registry investigation.120

DISCUSSION

There are several relatively different disease processes that can render a normally flexible vertebral column into a stiffened long bone-like structure which we combined under the acronym “SAD.” The biomechanics of the spine change dramatically in SAD, leading to a number of significant physiologic- and trauma-related implications. Although these pathomechanisms and their associated diagnostic criteria are well understood, our structured review of the more recent publications on the topic revealed 2 overarching themes:

  1. There is a noteworthy increase in publications on the topic of fractures in SADs, mainly on dealing with AS, but increasingly DISH and EAMS type conditions.
  2. Timely injury detection in SAD injuries remains unsatisfactory, despite ready availability of advanced imaging.

The question if these SAD injuries are getting more common cannot be conclusively answered at this time without more detailed epidemiologic data, as more numerous publications could represent an actual increase of these injuries due to demographic changes of a population leading longer but also more unhealthy lives or could be a sampling phenomenon as these injuries are transferred more readily to tertiary or quaternary care facilities, who then report on these injuries.

It is hoped that a persistently high incidence of missed and delayed diagnoses of fractures and injuries in SAD with a significant subsequent rate of secondary neurologic decline and additional deformity present a strong incentive to change present workup algorithms. The presence of an ankylosing condition of the spine is preferably picked up by emergency department physicians and radiologists as a key finding and in turn leads to pan-scanning of the spinal column with CT and/or MRI to more clearly visualize all areas of the spinal column and screen them carefully for less than obvious fractures including noncontiguous injuries. It is hoped that the very fact of detection of an ankylosing spine disorder leading to a screening scan will lead to a reduction of missed injuries. If in doubt, both CT and MRI scanning are preferable for less than apparent injuries to enhance the treating physicians' ability for detection. The importance of the presence of an ankylosing spinal disorder on the management and outcome of spine fracture treatments is reflected in the new AOSpine Injury Classification System, where a special modifier has been applied to reflect the significant impact of this entity.

As to treatment, the emergency services retrieval of patients with preexistent kyphotic spinal deformities seems to also benefit from improved awareness among providers. For neurologically intact patients, supporting the present position rather than seeking to place the patient supine on a rigid backboard would expose the affected patients to an increased risk of secondary neurologic injury. Traction is generally not recommended aside from very few and selected patients using low weights.

Form a clinical effectiveness perspective, the strength of evidence is however, a strong recommendation favoring surgery based on the limited data available can be clearly made. As to advances in treatment of SAD fractures, the most relevant variable is and remains arriving at a more timely injury detection. Fracture location, presence of noncontiguous injuries, and epidural hematoma are key radiographic findings relevant to SAD patients along with an understanding of which of the 3 major pathoentities the patient most likely fits to. For classification and general injury appreciation, the new AOSpine Injury Classification Systems for cervical and thoracolumbar spine injuries specifically address ankylosing disorders as a key variable. In addition to detection and classification of the injury, the underlying ankylosing disease pathology will offer important further insights into surgical treatment, such as decompression needs and considering some deformity correction.

For displaced injuries, posterior multisegmental fixation remains the preferred form of definitive treatment. For cervical injuries in AS, a temporizing anterior fixation can be considered to minimize the risk of displacement during rotation to a prone position.

Outcomes are heavily influenced by neurologic injury status and magnitude of medical comorbidities. One-year morbidity and mortality rates of patients with ankylosing spine injuries remain way poorer than those of patients with nonfused spinal columns. There are, however, suggestions that surgically treated patients have longer and better survivals than nonsurgically treated patients with SAD fracture dislocations.

Future research directions may look at decreasing delayed injury diagnoses, assessing the role of minimally invasive spine surgery and developing improved scoring capabilities to aid in treatment decision making for these frequently ailing patients.

In the meanwhile, the spine community is charged to improve dissemination of knowledge surrounding clinical recognition of ankylosing spine disorders among providers in other specialties.

CONCLUSIONS

In the ankylosing spine, the normally flexible spine is converted into a rigid structure which is more susceptible to fractures, even from trivial trauma-like falls from a standing or sitting position; therefore, patients with AS should always be suspected for spinal fractures and ligamentous injuries after any trauma, especially involving the cervical spine where most fractures have been reported in the literature.

Diagnosing spinal fractures in patients with AS can be challenging, and diagnosis is often overlooked initially; fractures are difficult to diagnose on plain radiographs and therefore, both CT and MRI have been recommended to identify spinal injuries in patients with AS. It is recommended that the entire spine be scanned in AS patients with a suspected fracture, so multilevel involvement can be considered and diagnosed.

Transferring AS patients with spinal injuries needs to be done very carefully to prevent neurologic deterioration. Although osteoporosis makes fixation of spine implants a significant concern, the literature has reported that most patients treated surgically had good outcomes.

Numerous studies have reported the risks associated with conservative management, such as pulmonary complications and decubitus ulcers with bed rest, poor tolerance to a halo, aspiration, and potential worsening of kyphosis, nonunion, neurologic decline, and loss of reduction.

Because of their increased risk for incurring spinal injuries from trauma, patients with AS need to be instructed to seek medical evaluation after an accident, even a trivial one.

Case 1

History and Examination

This sagittal MRI of a 60-year-old woman was obtained after she fell backward and struck her head while in the shower (Fig 1A). She complained of neck pain, but no sensory changes or motor deficits were identified. She was reassured and allowed to leave without immobilization. Without intercedent trauma, the patient was brought back to the emergency department just 2 days later for being unable to stand without assistance. On examination, she showed an ASIA A C7 SCI level. The subsequent imaging with CT and MRI of the cervical spine demonstrated an acute minimally displaced hyperextension fracture dislocation of the C5-6 vertebrae (Figs 1B, C).

Figures 1D, E demonstrate a staged anterior discectomy and fusion with plate fixation followed by a multilevel posterior decompression and fusion with segmental instrumentation. Postoperative sagittal MRI confirms the presence of full decompression and significant cord signal changes.

Postoperatively, the patient improved to an ASIA D status.

Case 2

This sagittal CT reconstruction of the thoracolumbar spine was obtained in a 78-year-old man with a previous history of L4-S1 fusion who presented with delayed fashion for severe back pain after a fall 10 days prior. The patient was found to be neurologically intact but suffered from multiple medical comorbidities. CT imaging confirmed DISH and an L1 bony hyperextension injury, subtype B3 of the AOSpine Thoracolumbar Classification System. Completion of imaging of the cervical and thoracic spines with MRI and CT was negative for additional fractures. The patient was essentially bedridden and unable to mobilize. Bracing was abandoned in light of his large abdominal girth.

After medical assessment and risk optimization, the patient was brought to the operating room and positioned on an adjustable Wilson frame with neurophysiologic monitoring in place. After removal of the old spinal hardware, segmental instrumentation was placed from T10 to S1, and an in situ fusion was performed as seen on the lateral radiograph. The patient enjoyed an uneventful recovery, mobilized without brace on postoperative day 1, and was discharged to a convalescent facility on postoperative day 4.

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Keywords:

spine fracture; ankylosing spondylitis; disseminated spinal hyperostosis; spinal ankylosis; unstable spine

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