The Use of Flexion-Extension MR Imaging for Accessing Cervical Spine Instability Resulting from “Rear End Low Impact” Auto Collisions
By Richard H. Adler
November 16, 2005
The May 2002 edition of Emergency Radiology published “The Use of Flexion and Extension MR in the Evaluation of Cervical Spine Trauma: Initial Experience in 100 Trauma Patients Compared with 100 Normal Subjects.” Emergency Radiology (2002) 9: 249-253. These ER radiologists noted that cervical spine trauma is common following rapid acceleration-deceleration, even during low-impact car collisions. However, flexion and extension x-rays, the typical imaging method initially employed in most clinical situations, is of very limited use poor utility in the evaluation of cervical spine structures such as tissues, discs, and ligaments.
The purpose of the study was to determine the value and utility of flexion and extension MR imaging in traumatized cervical spines following rear-end low-impact acceleration-deceleration injury motor vehicle collisions. 100 sub-acute injured patients were compared to age-matched normal subjects utilizing a rapid flexion and extension MR protocol.1 The assessment criteria for flexion and extension MR evaluation included (a) lordosis; (b) segmental spinal motion; (c) quantitative range of motion following full flexion and extension; and (d) cervical disc herniation.
The authors questioned the fundamental problem underlying the current definition of cervical instability. Defined as an angular motion greater than 11 degrees or translation of greater than 3 mm for adjacent spinal segments, the authors concluded that the definition of cervical instability does not appear to adequately represent true instability since no clear distinction exists between maximum physiologic flexion and partial subluxation due to partial ligamentous tear. The motion MR findings in injured subjects following low rear-end impacts trauma revealed injury to the posterior cervical complex, including the joint capsule, interspinous/supraspinous ligaments, and/or posterior portion of the annulus fibrosus.
As a result of their study, the authors believe that flexion-extension MRI can be very useful in cases of low-impact injuries in which there were clinical signs of cervical instability. Their procedure optimizes the detection of segment motions abnormalities and injuries of the disco-ligamentous complex. Biomechanical changes in herniated disc are also observed with their imaging protocol. The authors did note that their MR protocol is less reliable during the acute phase of injury (first 12 weeks) because of the presence of muscle spasm, which can exaggerate the biomechanical changes. They recommend the MR extension-flexion protocol during the sub acute phase (12-14 weeks after injury).
In clinical practice, all providers recognize that it is critical to determine the patient’s diagnosis, the cause of his/her injury, and which factors are likely to adversely affect their patients’ prognosis. The exact degree of injury and the probability of future pain in patients who have suffered cervical hyperextension/hyperflexion injuries may sometimes be difficult to ascertain. However, understanding the diagnostic and prognostic significance of cervical flexion-extension MR findings may provide useful information to the doctor, patient, insurance company, and attorney. For example:
- Physicians can predict with better accuracy the approximate length of treatment, probability of future care needs and provided a more accurate prognosis;
- Patients will have a better sense of what problems lie ahead and what type of restrictions on ADLs are reasonable and necessary;
- Insurer for at-fault party’s can establish accurate reserve for a fair settlement;
Legal counsel will be in a better position to understand his/her client’s treatment and rehabilitation and as a result better advocate for his/her client’s interests.1 During the period of April 2000 to March 2002, 100 adult normal asymptomatic subjects were selected from a random population, age-matched to 100 subacutely injured subjects following rear low-impact motor vehicle collisions. The age range was 18-53 years, with a mean of 35 years. The injured subjects were initially evaluated at the time of injury by qualified emergency physicians. Plain radiographs obtained at the time of injury were interpreted by qualified radiologists as “negative.” MRI was deemed clinically indicated following clinical assessment at 12-14 weeks after injury-the subacute period – due to the presence of continued neurologic symptoms, mainly neck pain and radiculopathy, despite clinically resolved muscle spasm.
Flexion and extension MRI was performed using supplies and accessories commonly available to most facilities. To perform flexion and extension MRI, the neck is positioned in the center of the coil on a head holder. The sides are padded with foam or Velcro pads to secure the cervical spine from side to side, permitting only forward and backward movements. A small foam dowel is positioned at the base of the neck for support. Movements are initiated under direct physician supervision, first to full flexion, and then to full extension, in two 90-s increments. The ten images are then formatted on a viewing screen and evaluated frame by frame for cervical lordosis and segmental motion, particularly the movements of the spinous processes and posterior elements. The integrity of the spinal cord and intervertebral disks is also assessed. The presence of superimposed disk herniation is also evaluated. Range of motion is quantified using the template method, using a standard software application available on most system workstations.