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Pitfalls and complications in the treatment of cervical spine fractures in patients with ankylosing spondylitis
© Heyde et al; licensee BioMed Central Ltd. 2008
Received: 06 December 2007
Accepted: 06 June 2008
Published: 06 June 2008
Patients with ankylosing spondylitis are at significant risk for sustaining cervical spine injuries following trauma predisposed by kyphosis, stiffness and osteoporotic bone quality of the spine. The risk of sustaining neurological deficits in this patient population is higher than average. The present review article provides an outline on the specific injury patterns in the cervical spine, diagnostic algorithms and specific treatment modalities dictated by the underlying disease in patients with ankylosing spondylitis. An emphasis is placed on the risks and complication patterns in the treatment of these rare, but challenging injuries.
The modified "New-York-Criteria" [1,5].
Lower back pain and stiffness for more than 3 months with improvement after exercise, but not with rest
Reduced motility of the lumbar spine in the sagittal and frontal axis
Restriction of the chest expansion (age and gender related)
Sacroiliitis at least grade 2 bilateral or grade 3–4 ipsilateral
Hehne und Zielke classification in ankylosing spondylitis .
Simple ossification of the dorsal spine bodies, no syndesmophytes
Incomplete anular ossification
Tender, the anulus fibrosus ventrally with or without lateral syndesmophytes, without overlapping of the vertebral bodies (incomplete)
Complete anular ossification
As type IIa, but with syndesmophytes overlapping the vertebral disc (complete)
Partial ostotic ossification
Thick and wide syndesmophytes, often with cortical- and spongiosa structure, corresponding the bamboo-type, but not present in all segments (incomplete)
Total ostotic ossification
As type IIIa, but several thoracic and lumbar segments are affected
Resulting kyphosis, spinal rigidity and secondary osteoporosis lead to changes of the biomechanical characteristics of the spinal column [10–13]. Secondary to kyphosis, the ventral displacement creates pathological tension and shearing forces to a spine with lacking flexibility [3, 12]. Furthermore, the reduced muscle activity and increased muscle degeneration causes an overall loss of muscle strength . The resulting posture change, with its pathologically elongated lever arms and reduced bone quality, can lead to serious injuries even after minor trauma mechanisms [3, 6, 8]. Frequently, no trauma is recalled by the patient, but rather an abrupt motion or other inadequate mechanisms [3, 6, 14]. Especially if a complete rigidity of the spine is present, i.e. Hehne and Zielke type IIb, III and IIIb (Table 2), there is an increasing risk sustaining such injuries [9, 12]. In these cases, the rate of neurological complications is extremely high, and special attention must be addressed to delayed or secondary neurological deterioration [3, 11, 14–16]. Neurological complications, however, are mostly seen in fractures with complete disruption.
The prevalence of ankylosing spondylitis ranges between 0.2% and 0.55% [18, 19]. Similar to the low prevalence of ankylosing spondylitis, vertebral fractures in case of ankylosing spondylitis represent a rare entity . Fractures of the cervical spine represent the most common level of injury in this patient population [4, 7, 20]. Centers with a high case load of spine trauma and a solid experience in the management of ankylosing spondylitis still have a low incidence of such injuries. Published series have usually been accumulated over a longer period of time [2, 3, 8, 12, 14, 16, 20, 21]. A questionnaire in 1071 patients with ankylosing spondylitis revealed a 5.1% prevalence of vertebral fracture history. Up to 14% of patients with ankylosing spondylitis will experience a clinically manifest vertebral fracture during their lifetime . A summary of published case series found cervical fractures to comprise 73% of vertebral fractures in ankylosing spondylitis (n = 130) . Sixty-five percent of patients with vertebral fractures in ankylosing spondylitis had neurological deficits . The drawing attention to these injuries is a result of the specific and uncommon fracture configuration with sometimes grotesque dislocations, the high rates of neurological complications and the challenging surgical management. The male to female ratio is 2.5:1 in the prevalence of the disease, and the incidence of cervical spine injuries is higher in males [3, 8, 12, 14, 16, 20]. One study reported a prevalence of vertebral fractures of 6.2% among males and 4.6% among females . Most studies report an average age of 60 years or slightly higher [14, 21, 23]. Affected patients usually have a long disease progress and a "peak" during the second or third decades after their initial diagnosis . The average disease duration at the time of vertebral injuries was 24.0 ± 11.5 years after onset . Injuries are mostly localized in the lower cervical spine (C5/6 and C6/7) and in the cervico-thoracic junction, although any area of the cervical spine may be affected [3, 8, 20, 25]. Furthermore, cervical instability secondary to rheumatoid destruction, has been observed in the upper cervical spine. These changes have to be considered both in the diagnostic work-up and the therapeutic approach [8, 26]. Simple falls, followed by motor vehicle accidents and high energy trauma, are among the most common mechanisms of injury of the cervical spine in these patients [3, 20].
Fracture classification in ankylosing spondylitis according to Metz-Stavenhagen et al. .
Complex fracture pattern involving anterior and posterior – bony and ligamentous structures of the spine at the level of injury
Asymptomatic or mildly symptomatic multi-level spinal injuries are more often described in the literature. Therefore, it is recommended to search carefully for associated cervical spine injuries and to radiologically clear the entire spine [8, 13, 14, 20, 34]. Scintigraphic bone scans can be helpful for screening a patient, especially if he cannot be placed in the MRI due to the spinal deformity. Nevertheless scintigraphy looses its diagnostic value ten days after the initial trauma . Furthermore, scintigraphy is not specific for fractures and is therefore not the first choice in the acute phase [20, 32, 35].
The primary goal of treatment is bony healing without significant loss of reduction. The literature provides recommendations for both non-operative and operative treatment. Indications for operative treatment are based on the criteria for instability, incorrect posture, pain and neurological deficit . Frequently, a Halo external fixator is recommended for the initial stabilization if a planned surgical treatment has to be delayed . The topic of whether surgical correction of pathological spinal posture is truly relevant remains controversial. This is of special interest in fractures of the cervical spine and the junctional areas [12, 20]. Spinal correction thought to be secondary to the main therapeutic goal of fracture stabilization [2, 6, 20].
Non-operative treatment strategies can only be successful if an adequate stabilization and realignment of the cervical spine are achieved in all planes. For this purpose, an external fixation with the Halo is usually required. The expected duration of treatment until fracture healing is somewhere between ten to sixteen weeks . Because of the often highly unstable fractures, the osteoporotic bone, compromised skin quality, and pathological chest rigidity, Halo treatment is associated with a high complication rate and a high risk of non-unions [6, 8, 11–14, 23]. Loss of reduction, non-union and neurological deterioration have been reported after non-operative treatment, which often leads to secondary surgery [3, 20, 30]. In older fractures with consecutive severe kyphotic deformities, primary non-operative treatment can be advisable. In these cases, the Halo fixator allows gentle and stepwise correction prior to definitive operative fixation [12, 20]. History recommendations suggested treatment in traction [2, 30, 37]. According to recent publications and also to our own experience, such treatment strategies are not to be recommended due to the associated long-term immobilization and to complications related to bed rest and to Halo fixation [3, 12, 14, 20].
Key studies related to surgical stabilization of cervical spine fractures in ankylosing spondylitis.
Preoperative neurological compromise
Outcome of stabilization
Olerud et al. 
Retrospective case series
Anterior and posterior stabilisation
Taggard & Traynelis 
Prospective case series
All survivors with solid fusion after 3 months
Guo et al. 
Retrospective case series
Anterior and posterior
All survivors with fusion at final follow-up
Cornefjord et al. 
Retrospective case series
Posterior and combined
Fusion in all patients
Zdichawski et al. 
Retrospective multicentric case series
Anterior, posterior, and combined
3 cases with implant failure (all cases anterior-only)
Retrospective case series
Anterior, posterior and combined
Fusion in all survivors
Einsiedel et al. 
Retrospective multicentric case series
Anterior, posterior and combined
5 cases with early implant failure (all cases anterior only)
• Anterior stabilization
Anterior stabilization may be ideally performed in patients with good bone quality, where the fracture can be precisely reduced and perfect axial alignment can be obtained [3, 12]. With an anterior approach, the feasibility for long-distant fixation is limited. As a primary measure before the patient is put into prone position it secures the spine and reduces the risk for a neurological complication during positioning. In cases of severe deformity, the anterior approach to the cervical spine may not be possible. The anterior-only stabilization is rarely performed due to the aforementioned conditions. Further, posterior and combined approaches demonstrate a higher biomechanical stability [3, 12, 38, 39].
• Posterior stabilization
Posterior stabilization is recommended for unstable fractures with the risk of possible translation and with a sufficiently stable anterior column [6, 23]. Fox et al.  recommend the use of a Halo fixator after posterior stabilization, until fracture consolidation is radiologically documented. Other authors demonstrated good results without a Halo fixator after an extended posterior stabilization [20, 23]. Improved stability of the posterior rod and screw fixation was described after the use of cervical pedicle screws compared to lateral mass screws [20, 38].
• Combined 360°-fusion
During aftercare, patients have an increased risk of developing severe complications due to their preexisting rheumatoid disease [3, 44]. The reduced pulmonary function caused by kyphosis, chest rigidity, reduced diaphragmatic expansion and the potential presence of fibrosis increase the risk for pulmonary infections. This represents the main cause of post-operative mortality [6, 8]. Hence, fractures need to be stabilized in a way that allows an aggressive early post-operative mobilization.
The reduced skin resistance, attributed to the rheumatic disease, can provoke the formation of pressure sores even in the area of the rigid cervical collar . Attention should be paid to the Halo fixators for possible pin tract infection. The pins of a Halo fixator are also at an increased risk of loosening in case of osteoporotic bone quality .
All of these problems may lead to increased morbidity and mortality in the postoperative treatment [2, 6, 13, 20]. Olerud et al.  described an increased complication rate in elderly patients and in patients with preexisting neurological deficit. At the same time, the mortality rate for ankylosing spondylitis patients with a cervical fracture is higher than in a comparison group with only a cervical fracture. The main goal, therefore, is an early postoperative mobilization without the aid of Halo fixators. In our opinion, a long instrumentation with a combined dorso-ventral 360° fusion is the best option that allows early postoperative mobilization of the patient with ankylosing spondylitis.
As outlined in this article special attention required in patients with ankylosing spondylitis with suspected cervical fractures. Due to the low prevalence of this particular underlying disease in the general population these injuries are a rare finding [4, 7]. Injuries of the cervical spine of these patients may occur even after minor traumas, and in certain cases, patients do not recall any trauma [3, 6, 8, 12]. The rigidity of the spine, the resulting kyphotic deformity, the associated osteoporosis, and the degenerated stabilising muscles lead to an increased vulnerability of the spinal column. The resulting prolonged lever arm influences the evident pathological posture [12, 14, 16, 20]. Therefore, a meticulous screening of the entire spine is necessary in these patients with new onset or increased pain, posture alterations of the head or change in forward gaze [8, 13, 14]. The required checkup should not only include the clinical and neurological examination, but also a standardized radiological work-up. The x-ray validity, however, is often reduced because of the morphological specifics, osteoporosis, and the often unrecognizable thin fracture line in non-displaced fractures [7, 10, 31]. Therefore, a thin-cut (2 mm) multislice CT with 2-D reconstructions of suspicious areas is strongly recommended. Further, an MRI is necessary for unclear statements and for questionable situations, such as spinal canal compromise with neurological deficits [6, 11, 17, 20, 32, 33].
Injuries of the lower cervical spine and the cervicothoracic transition prevail in the cervical spine [12, 20, 25]. Complex fracture patterns with severe dislocation and neurological impairment are to be found above average [2, 14, 16, 20].
As outlined above, two distinct classification systems have been proposed for cervical fractures in patients with ankylosing spondylitis. The standard classification by Magerl and colleagues  is of limited use for this particular patient group, due to significantly altered anatomic morphology. The classification by Metz-Slavenhagen  considers complete disruption of the entire spine and consecutive sintering. Thus, incomplete fractures are missed by this classification scheme. Due to the weaknesses of both classification systems for patients with ankylosing spondylitis, we recommend the additional descriptive characterization of individual fracture patterns.
The main goal of treatment is the stabilization of the fracture in the correct position until complete fracture healing is achieved. Surgical procedures offer advantages compared to non-operative treatment options as mentioned above [12, 14, 20]. There is no consensus in the literature regarding on favorable operating technique. Isolated anterior stabilizations are rarely indicated . The frequently recommended posterior-only instrumentation results in higher stability opposed to the single ventral stabilization, especially using angle-stable devices [6, 21, 23]. The combined anterior-posterior or posterior-anterior approaches are preferred due to the resulting higher primary stability. To start surgery in prone position reduces the danger of neurological deterioration during positioning and allows a first reduction and stabilization in a safe way [3, 11, 12, 14, 16, 20]. Agreement is obtained on the need for long instrumentation in order to obtain a better distribution of the resulting forces at the bone-implant interface [3, 11, 12, 14, 20, 23].
Due to its increased vulnerability, the spinal column of patients with ankylosing spondylitis is compromised during every therapeutic procedure [17, 20]. This includes the transport and positioning of the patient, as well as anesthesia, surgical procedures and the postoperative rehabilitation. Therefore, a standardized management is required in patients with ankylosing spondylits, including fiberoptical intubation, appropriate transport maneuvers and positioning under the avoidance of any brusque manipulation. Other relevant items are consequent vital sign monitoring, periodic neurological checkups and thorough examinations into newly occurring symptoms [6, 8, 20, 41, 42]. A stable and safe surgical stabilization which allows immediate postoperative mobilization remains a main goal of treatment. Therefore an appropriate standardized workup, the consideration of specific aspects regarding both the underlying disease and the particular risk of the biomechanically altered spine are of high importance for an adequate outcome in this special patient group. [2, 3, 6, 12, 14, 20, 23, 44].
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