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Diagnosing purely ligamentous injuries of the cervical spine in the unconscious trauma patient

¹ University of Oxford Medical School, William Osler House and ² Department of Radiology, John Radcliffe Hospital, Oxford OX3 9DU, UK

	Introduction

Top Introduction Flexion/extension studies Magnetic resonance imaging Conclusion References

 
An injury to the cervical spine is thought to occur in up to 3% of patients with significant trauma and up to 10% of patients with serious head injury [1]. The most appropriate method of determining stability of the cervical spine in the unconscious trauma patient is an area of controversy and practice varies significantly between hospitals. For any patient who has suffered major trauma, the spine must be considered unstable until there is evidence to the contrary, because the consequences of missing a cervical spine injury can be devastating, including long-term disability and death. The cervical spine should be immobilized using a hard cervical collar and this collar should remain in place until an unstable injury has been ruled out.

The difficulty in assessing cervical spine stability in the unconscious patient arises from the inability to obtain a reliable history and clinical examination. The diagnosis must therefore be determined radiologically and it is the choice of the most appropriate radiological tests in these patients that remains a topic of much debate.

Initial assessment of the cervical spine in the unconscious trauma patient commonly involves a lateral view plain radiograph as part of an Advanced Trauma Life Support (ATLS) protocol. This is followed by a three-view plain radiograph series (lateral, anteroposterior and odontoid views) and either CT of areas poorly visualized on plain radiographs or CT of the whole cervical spine. The sensitivity of three-view plain radiographs in identifying cervical spine injury has been estimated at 93% [1] and this is further increased by the addition of CT [2]. More recently, with the introduction of multislice technology, there has been a trend to perform whole cervical spine CT as the first-line imaging technique instead of plain radiographs.

Whilst there is debate over the most appropriate use of CT in addition to plain radiographs in the initial assessment of major trauma victims, the most contentious issue in clearance of the cervical spine (ruling out any form of unstable injury) is what the next step should be if both plain radiographs and CT show no abnormalities. The absence of an unstable fracture on plain radiography or CT may not allow safe discontinuation of immobilization [3] as there remains the potential for an undisplaced purely ligamentous injury of the cervical spine. Plain radiography and CT are unable to reliably demonstrate ligament damage and other soft tissue injury that could render the cervical spine unstable [4].

The incidence of ligamentous injury of the cervical spine without fracture is low and a retrospective study over 3 years by Chiu et al has estimated it to be 0.5% of blunt trauma admissions with a Glasgow Coma Scale of less than 15 [5]. However, the incidence of purely ligamentous injuries that are not diagnosed during admission and which subsequently result in neurological deficit is unknown. The only certain way that the incidence of undiagnosed injuries could be determined would be to follow-up trauma patients in whom the cervical spine had been cleared to see how many later developed a neurological deficit attributable to the original trauma.

One option in the unconscious patient with negative plain radiographs and CT would be to leave the collar in place until a reliable examination can be performed. However, patients who have significant head trauma may never be able to reliably report neck pain or sensory deficits and the time taken for an unconscious patient to regain consciousness is unpredictable. More importantly, there is significant morbidity associated with prolonged use of a cervical collar with half of patients developing decubitus ulceration of the skin after 5 days [1, 6]. The presence of a collar and a delay in clearing the cervical spine present many nursing and medical complications including the necessity for a four-person log-roll for any movement of the patient and difficulties with intubation, extubation and central venous access. Furthermore, a cervical collar may not provide complete immobilization of cervical movement [7]. Early clearance of the cervical spine is therefore highly desirable so that the collar can be removed as soon as possible.

In some centres, protocols will allow the spine to be cleared by a negative, good quality CT. The justification for this policy is the low number of recorded cases of proven instability following a negative CT. Because it is difficult or impossible to detect the rare undisplaced purely ligamentous injuries on CT, other protocols specify the requirement for additional flexion/extension studies or MRI.

	Flexion/extension studies

Top Introduction Flexion/extension studies Magnetic resonance imaging Conclusion References

 
Stability in an unconscious patient can be assessed directly by imaging the cervical spine under passive flexion and extension. Flexion/extension views can be obtained either statically, in which plain radiographs are taken at maximum flexion and extension, or dynamically using fluoroscopy, in which the spine can be observed throughout the range of movement. The patient is maximally sedated to prevent any unwanted movement and the cervical collar is removed. Limited flexion and extension is initially performed and intervertebral body motion (subluxation and angulation) is observed throughout, looking for evidence of instability. The range of movement is then gradually increased until maximal flexion and extension are reached. It is thought that dynamic screening is safer than static imaging because the procedure can be stopped if an abnormality is detected on partial flexion or extension.

Several studies have evaluated the use of flexion/extension views in clearing the cervical spine in unconscious trauma patients. Brooks and Willett studied 210 unconscious trauma patients between 1994 and 1997 [8]. Of these, 78 underwent dynamic fluoroscopy of the cervical spine and only one patient showed signs of instability without evidence of fracture on plain radiography or single slice CT. This patient demonstrated atlantoaxial instability on dynamic fluoroscopy. Plain radiographs had shown "minor increase in soft tissue shadow and a questionable increase in interspinous distance", although a CT scan of the upper cervical spine was reported as showing no abnormality.

In a study by Davis et al, dynamic fluoroscopy was performed on 116 patients with normal findings on plain radiography and CT, only one of whom showed instability without fracture [6]. This patient showed 2 mm of subluxation on flexion, but it was felt that this was only a minor ligamentous injury.

Ajani et al prospectively studied 100 trauma patients [1]. 91 of these patients survived long enough for data collection. Of these, one patient was found to have an unstable cervical spine injury only detected on flexion/extension views. In this patient the three-view plain radiographs were re-reviewed, and re-confirmed as showing no abnormality.

A further study has been performed by Sees et al in which dynamic fluoroscopy was performed on 20 patients, all of whom underwent at least three-view plain radiographs before fluoroscopy [9]. In one of these patients, flexion/extension views showed a C4/5 subluxation that was not evident on plain radiography. A subsequent CT scan revealed fractures of the left C4/5 facet joint and the left C6 pedicle and lamina. A policy of performing CT of the whole cervical spine would have avoided the need for flexion/extension views in this case.

Griffiths et al reviewed 479 passive flexion/extension examinations in obtunded patients and found that none of the studies influenced the decision to proceed to surgical stabilization [10]. 59% of examinations were deemed of insufficient quality due to inadequate flexion or extension or visualization.

There were no complications associated with the dynamic fluoroscopy procedure in any of these studies. However, it is questionable whether any one of these studies provides a true assessment of the safety of dynamic fluoroscopy. The incidence of unstable cervical spine injury evident only on flexion/extension views is very low. Given that it is only this subset of patients that is at a potential risk from the procedure (patients with a stable cervical spine are not at risk from flexion/extension studies), the sample size is too small to make an assessment of the risk of the test. Studies that report 100% safety of the procedure when just one or two patients were ever at risk of any injury need to be interpreted with caution.

The safety concerns regarding flexion/extension studies are that they could provoke neurological damage in patients with instability and a narrowed spinal canal due to pre-existing degenerative disease, ossification of the posterior longitudinal ligament or traumatic disc herniation. The procedure itself involves movement of the cervical spine without simultaneous knowledge of the effect it may be having on the patient. The unconscious patient is unable to complain of pain or sensory changes during the procedure and it is only once the patient regains consciousness that any neurological impairment would be evident. In this situation it may be difficult to prove that the procedure did not contribute to the neurological deficit, particularly if subsequent MRI shows central canal narrowing at the level of the cord injury. Given the low incidence of purely ligamentous injuries, the probability of any one centre admitting several such patients is very low and the only way that the true safety of flexion/extension views can be assessed is by a large multicentre study.

	Magnetic resonance imaging

Top Introduction Flexion/extension studies Magnetic resonance imaging Conclusion References

 
MRI is the alternative to flexion/extension studies in determining the stability of the cervical spine in an unconscious patient with no evidence of fracture on plain radiography or CT. Whereas flexion/extension views provide a direct assessment of the stability of the cervical spine, the integrity of the soft tissues seen on MRI provides an indirect assessment of stability. MRI is an extremely sensitive modality for detecting epidural haemorrhage and oedema and soft tissue injury, including ligament damage, intervertebral disc herniation and spinal cord injury [11].

The advantages of MRI compared with flexion/extension studies are that the cervical spine can remain immobilized until stability has been determined and that MRI does not involve the use of ionizing radiation. Few studies have evaluated the use of MRI in the acute trauma setting and it is not routinely used in most trauma centres.

In one study of 121 trauma patients, MRI demonstrated soft tissue injury that was not evident on plain radiography in 31 patients (26%) [12]. Of these 31 patients, 8 required surgery and MRI was the first test to identify the injury. However, it is important to note that in this study MRI was performed before CT with CT being used to target abnormal areas on MRI. CT revealed that 13 of the 31 patients had in fact suffered fractures that were not visible on plain radiographs and of the 8 patients requiring surgery, only one showed no evidence of fracture on plain radiography or CT. Therefore, if CT had been performed before MRI, MRI would have only detected one additional significant injury out of 121 patients (0.8%).

However, it remains unclear which MRI-detected ligamentous injuries are of clinical significance and many of the injuries detected by MRI may not indicate significant instability. This begs the question of what should be done in patients in whom MRI does not give a definitive assessment of stability. In these rare cases, the next step could be flexion/extension studies. A prior knowledge of a capacious spinal canal from MRI would eliminate much of the concern of performing this test. Evidence of canal narrowing would suggest that flexion/extension studies should not be performed.

The disadvantage of MRI most commonly cited is that it is difficult to perform in the acute setting. The absence of MRI-incompatible ferromagnetic objects in the body must be confirmed beforehand which may be difficult in an unconscious patient and much of the intensive monitoring equipment that these patients require may not be compatible. This may limit the practicality of performing MRI on trauma patients, although MRI-compatible intensive therapy equipment is becoming increasingly available. In addition, the imaging time of MRI is relatively long and may therefore be inappropriate in haemodynamically unstable patients. MRI also has greater susceptibility to patient motion, so restlessness or agitation will interfere with the scanning.

There are the additional problems of the availability of MRI and of its higher cost compared with dynamic fluoroscopy. However, the number of unconscious trauma patients admitted with negative plain radiographs and CT and who require further assessment of cervical spine stability is relatively low (78 such patients were admitted in a 3 year period at the John Radcliffe Hospital in Oxford, a major trauma centre [8]), and it would seem difficult to argue against performing MRI purely from a cost-effectiveness angle.

There has been a scarcity of good studies on the use of MRI in clearing the cervical spine in unconscious patients, which may in part be due to the practical difficulties associated with performing routine MRI scans in these patients. However, the use of MRI in these patients is feasible particularly in departments where the scanner is located close to the intensive care unit. Open configuration scanners, which are becoming more readily available, remove many of the problems of monitoring the critically ill patient during their scan.

	Conclusion

Top Introduction Flexion/extension studies Magnetic resonance imaging Conclusion References

 
An unstable, purely ligamentous injury of the cervical spine is a rare occurrence, but failure to diagnose this lesion can have serious implications. Negative plain radiographs and CT do not rule out this type of injury and additional radiological techniques are therefore required. Because of the rarity of these types of injuries, there is little evidence in the literature to guide the optimum protocol for imaging high-risk patients. The recent improvements in CT technology have resulted in rapid scans with excellent image quality in both the axial and reconstructed planes. Many centres will consider a negative, good quality CT as sufficient evidence to clear the cervical spine. Although complications of passive flexion/extension views are not evident in any of the reported studies, a larger study is required before the safety of this technique is known. MRI allows the spine to remain immobilized until its stability is known and thus does not present the same potential dangers as flexion/extension studies. However, there are practical difficulties associated with performing MRI in the acute setting and it is not yet fully clear which MRI findings are of clinical significance. MRI can exclude lesions that could make flexion/extension studies potentially harmful, and which would not be evident on plain radiography or CT. Further assessment of the feasibility of performing MRI in the acute setting is required if it is to become the technique of choice in clearing the cervical spine of purely ligamentous injuries.

Received for publication October 15, 2003. Revision received December 8, 2003. Accepted for publication December 23, 2003.

	References

Top Introduction Flexion/extension studies Magnetic resonance imaging Conclusion References

 

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