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Assessment of the "nearly normal" cervical spine radiograph: C2-C3 pseudosubluxation in an adult with whiplash injury
  1. P Curtin,
  2. J McElwain
  1. Department of Trauma and Orthopaedics, Adelaide and Meath incorporating the National Children’s Hospital, Tallaght, Dublin 24, Republic of Ireland
  1. Correspondence to:
    Dr P Curtin
    Department of Trauma and Orthopaedics, AMNCH, Tallaght, Dublin 24, Republic of Ireland;


C2-C3 pseudosubluxation is a well recognized normal anatomical variant in children and this physiological spondylolisthesis often makes the interpretation of paediatric cervical spine radiographs difficult. In direct contrast, this finding is rare in adults and has not been reported as a diagnostic difficulty following neck injury. We report a case of C2-C3 pseudosubluxation occurring in a 27 year old woman presenting with neck pain 1 week after a road traffic accident. Although there are effective radiological guidelines for cervical spine radiograph evaluation in children, there is no evidence that these can be applied to the adult cervical spine. Flexion and extension cervical spine views have limitations. In such cases, magnetic resonance imaging is required to definitively exclude pathological injury.

  • ED, emergency department
  • C2-C3 pseudosubluxation
  • adult
  • cervical spine
  • whiplash injury

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Neck pain following whiplash injury is a common presenting complaint in emergency departments, and clinicoradiological evaluation of the cervical spine (cervical spine) is often difficult. The incidence of missed injury ranges from 4% to 8% of cervical spine injuries,1–,3 and failed or delayed diagnosis can cause potentially catastrophic sequelae.3 The lateral cervical spine radiograph has an overall diagnostic sensitivity of 74–86% for skeletal injuries, and increases to nearly 100% when anterior-posterior and open mouth odontoid views are added.4 In non-skeletal injuries, the lateral view is diagnostic in 97% of cases.3

Pseudosubluxation is a normal anatomical variant in which, because of ligamentous laxity, there is physiological misalignment and anterior slippage of the body of C2 on C3. It is found in up to one fifth of children under 16 years of age5 and is usually recognisable on plain radiographs.5,,6 In adults, this type of anterolisthesis can be normal if <3 mm, but is a rare finding.3,7,,8

In this report, we present a case where C2-C3 spondylolisthesis complicated cervical spine assessment following injury. We discuss the clinical management of such cases. Although there are effective radiological guidelines for children,5,,6 there is no evidence that these can be applied to the adult cervical spine or that they obviate the need for further imaging to rule out pathological injury.


A 27 year old woman was referred to the hospital radiology department by her primary care physician for cervical spine radiographs. She complained of pain and stiffness in her neck and left shoulder 1 week following a road traffic accident. Another vehicle had driven into the back of her car while it was stationary, and shunted it into the back of the vehicle in front, causing severe damage to her car. She was the driver at the time, and had been wearing a seat restraint. She felt physically well and did not seek medical advice until 5 days later when she developed stiffness and pain. Her symptoms failed to respond to anti-inflammatory medication. Cervical spine series showed a grade I spondylolisthesis of C2-C3 (fig 1), the only abnormal finding, upon which she was referred to the emergency department (ED) for further clinical assessment and orthopaedic review.

Figure 1

 Lateral cervical spine radiograph showing anterolisthesis of C2 on C3, measuring 3 mm. The posterior cervical line drawn from the cortex of the posterior arch of C1 to that of C3 lies 2 mm from the cortex of the posterior arch of C2.

In the ED, the patient was treated as an acute cervical spine injury. Clinically she had left cervical paraspinal tenderness. There was no midline bony tenderness and no neurological deficit, and she could lift her head without pain. Review of her lateral cervical spine radiograph showed anterolisthesis of C2 on C3, measuring 3 mm, and a significant loss of normal cervical lordosis indicating muscle spasm. There was no prevertebral swelling. Flexion and extension lateral cervical spine radiographic views (erect) were performed under orthopaedic supervision (fig 2). These were well tolerated by the patient, whose symptoms and neurological status remained unchanged.

Figure 2

 Extension lateral cervical spine radiograph showing normal alignment of the upper cervical spine. Flexion lateral cervical spine radiograph; the measurement of the deformity is the same as in fig 1, with anterolisthesis of C2 on C3 of 3 mm and the posterior arch of C2 lies 2 mm from the posterior cervical line drawn from C1 to C3.

MRI of the upper cervical spine ruled out disc or ligamentous injury (fig 3) and the patient was reassured, referred to the physiotherapist and discharged with appropriate analgesia.

Figure 3

 Sagittal T2 MRI images demonstrating the ligamentous integrity of the upper cervical spine.


Cervical spine radiographs are highly sensitive3,,4 but not always specific. Accurate diagnosis is highly dependent upon observer experience. The presence or absence of prevertebral soft tissue swelling is not reliable in predicting or excluding hidden bony or ligamentous injury,9–,11 but a loss of alignment or subluxation between two contiguous vertebra usually indicates occult skeletal or non-skeletal injury. A pseudosubluxation or physiological anterolisthesis of C2 on C3 can also occur, and usually measures no more than 2 mm. It is common in children,5 but in adults, has been reported at C2-C3 or C3-C4 only as a rare incidental finding.8

In both children and adults, C2-C3 pseudosubluxation must be distinguished from a traumatic spondylolisthesis caused by a "hangman’s fracture" (fracture of the pars interarticularis of C2). To aid diagnosis, Swischuk6 defined a posterior cervical line drawn between the anterior cortices of the posterior arches of C1 and C3. Swischuk examined and compared the radiographs of 26 children with physiological subluxation and eight children with traumatic spondylolisthesis. He found a major radiological difference between the two groups and suggested that if the anterior cortex of the posterior arch of C2 lay within 1.5 mm of the posterior cervical line, then a traumatic spondylolisthesis was unlikely.6 In adults, it is not known whether this observation applies. In this case, the difference was 2 mm, but there was no pars fracture.

Biomechanical studies have shown that in upper cervical spine injury, a ligamentous injury is more likely when the mechanism is hyperflexion.12 The purpose of flexion and extension views is to assess the integrity of the posterior ligament complex.13 Flexion views in this case showed no measurable worsening of the spondylolisthesis and it appeared to resolve in extension. The value of normal flexion and extension radiographs in the acute setting when neck pain is present, is however, uncertain.14 We completed our investigations with a magnetic resonance image, which although expensive, is the definitive screening investigation for non-skeletal injury.

The incidence of missed injuries of the cervical spine is high,1–,3 and failed or delayed diagnosis can cause potentially catastrophic sequelae.3 Abnormalities of the cervical spine, however subtle, should be evaluated definitively. From the patient’s perspective, an accurate and early diagnosis should lead to better treatment and improved outcome, and also simplifies any future medicolegal issues.


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  • Competing interests: none declared