Delayed Cervical Spine Instability

I found an online course on MRI Spinal Interpretation to be very instructive on the topic of Delayed Cervical Spine Instability.  I highly recommend it, and I can tell you that you won’t appreciate how much it will help you as a clinician until you take it for yourself.  It can be found at this website, www.teachdoctors.com, and it is taught primarily by Mark Studin, DC, and Robert Peyster, MD, who is a neuroradiologist, and actually does most of the good teaching.  The reason I bring him up here is because one thing Dr. Peyster mentioned while going over the interpretation of the cervical spine was that finding lesions in the interspinous ligaments was extremely important, as that sort of damage is typically hidden by acute muscle guarding for several weeks after an MVC.  He stated that he had personal knowledge of patients who had incurred permanent spinal cord injury when the muscle guarding let up, and bony impingement on the cord occurred.   Now, I have never seen this, or had it reported to me, and I diagnose interspinous ligament damage a lot, using the formula found in an article written by Aaron C. Eubanks, MD, et al.  (Reference data for assessing widening between spinous processes in the cervical spine and the responsiveness of these measures to detecting abnormalities, The Spine Journal 10 (2010) 230-237).  But while searching for articles about spinal instability, I came across this gem:

Wilberger, Jack E., and Maroon, Joseph C.  Occult Posttraumatic Cervical Ligamentous Instability.  Journal of Spinal Disorders, Vol. 3, No. 2, 1990: 156-161

The authors worked in the Neurotrauma Department at Allegheny General Hospital in Pittsburgh, PA, and their study involved a review of the 1,451 trauma patients their department saw during 1987 and 1988, and evaluated for possible cervical spine injury.  Initially, a five view cervical spine series was performed, and after bony injury had been ruled out, flexion-extension views were obtained in 217 of these patients.  Using the parameters of White and Panjabi (3.5 mm/>11 degrees) for horizontal and angular displacement, they were able to identify significant spinal injury immediately in 110 of these patients.  Now here’s where it gets interesting:

Sixty-two of the 217 patients (this does not include any in the group of 110) had the flexion-extension projections repeated 2-4 weeks later for the following reasons:

  1. Inadequate initial study due to poor effort or limitations in motion (n=37)
  2. Clinical concerns over initial studies in spite of meeting normal radiographic criteria (n=10)
  3. Persistent or new symptoms of neck pain (n=14)
  4. Development of neurological symptoms (n=1)

Significant ligamentous instability was subsequently documented in eight of these patients.

On the initial lateral and flexion-extension radiographs in all eight patients, horizontal displacement (it doesn’t mention if this anterolisthesis or retrolisthesis) ranged between 1.5 to 3.0 mm., and angular displacement ranged from 5-10 degrees.  On the repeat radiographs 2-4 weeks later, horizontal displacement increased to 3.8 to 7 mm. and angular displacement increased from 13 to 22 degrees.  All patients subsequently went on to cervical fusion surgery.

Evidently the problem of delayed cervical spine instability after trauma has been a concern of spinal surgeons for a long time.  The authors mention that of all the factors involved in assessing spinal stability, the status of the ligaments was the most difficult to evaluate.  They listed several factors that might obscure incipient severe ligamentous injury in the acutely injured patient, such as the general acceptance of a “normal” degree of spinal ligamentous laxity in younger patients, the presence of cervical myospasm, and the failure to obtain flexion and extension views of the injured cervical spine.  They listed direct evidence of instability (White and Panjabi’s 3.5 mm/>11 degrees criteria), and indirect signs of ligamentous injury, such as widening of the interspinous distances and prevertebral soft tissue swelling.  Their recommendations included taking  flexion-extension radiographs as a routine part of the initial evaluation, once bony injury had been ruled out, and that if any horizontal displacement exceeded 1.5 mm and/or angular displacement exceeded 5 degrees on either lateral or flexion-extension films, that the possibility of significant ligamentous injury should be considered.  When these findings were present, they  recommended maintaining the patient in a rigid cervical collar for 2-4 weeks, and then repeating the flexion-extension films.  And if evidence of continuing instability was present, or if the instability was progressive in nature, then surgical fusion was recommended.

Notice that in this article the only thing considered to be an injury worth monitoring is the one in which the limits prescribed by White and Panjabi are surpassed.  Remember, when translation is greater than 3.5 mm in one direction, or angular displacement is greater than 11 degrees greater than adjacent segments (which are also the standards used in the AMA Guidelines for Evaluation of Permanent Impairment, 6th edition), only then is injury diagnosed.  Anything less than that, according to the standards, is normal.  But how does that make any sense?

Any displacement of a vertebra of >3.5 mm. is considered to be a third degree sprain, which means that 75-100% disruption of the ligament’s collagen fibers has occurred.  If I have a displacement of 3.3 mm., I’m normal; if I displace just .2 mm more, then I’m 75%+ disrupted, and I require a surgical solution to restore stability.   Right……..

My point is that modern computer mensuration analysis of cervical sagittal movement has established that the amount of normal motion between vertebrae is a lot less than 3.5 mm.  White and Panjabi’s standards were established with the publication of their first edition of Clinical Biomechanics of the Spine (1981)(actually, this appeared in an earlier article, published in 1976), before MRI and modern computers were ever invented.  They also based all of their inferences on observations they made of cadaver spines, and not live ones, and there is always a huge difference in tissue properties when you consider dead vs. alive.  When dealing with live spines, Lin et al. (Characteristics of Sagittal Vertebral Alignment in Flexion Determined by Dynamic Radiographs of the Cervical Spine.  Spine Vol. 26(3), 1 February 2001, p.256-261) established that from extension to flexion, the change in George’s Line should amount to less than 0.06 mm.  Wu SK, et al. (The Quantitative Measurements of the Intervertebral Angulation and Translation During Cervical Flexion and Extension.   European Spine Journal, Sept. 2007; 16(9):  1435-1444) determined that normal translation, during flexion and extension in the cervical spine, ranged from 0.4 mm to 1.2 mm, depending on what level of the cervical spine you were talking about.  And Anderst WJ, et al. (Validation of a Non-Invasive Technique to Precisely Measure In Vivo Three-Dimensional Cervical Spine Movement, Spine March 15, 2011; 36(6): E393-E400) determined that anterior-posterior translation in flexion-extension above a fusion averaged 0.4 mm, and below a fusion, 0.7 mm.

Spinal Kinetics handles this one well.  They employ board certified medical and osteopathic radiologists who draw the lines for spinal analysis and not only apply the AMA standards, but they also include what’s known about the three grades of ligament sprain:

0.6-1 mm.=  grade I sprain

1.0-3.4 mm.=  grade 2 sprain

>3.5 mm.=  grade 3 sprain

The MD’s at Spinal Kinetics, at least, recognize that just because the total translation doesn’t exceed 3.5 mm., that doesn’t mean that the ligament is not damaged.  They are saying just the opposite, and further state that they consider the grade 1 sprains to be minor injuries and the grade 2 and 3 sprains to be major injuries.  Ligament injuries are ligament injuries regardless of the degree of increased translation or increased angulation.

The guidelines for the use of digital motion x-ray in clinical practice for chiropractors which were written by the American Chiropractic College of Radiologists (ACCR) in 1989 suggest that motion x-rays should be done 6-12 weeks after the precipitating event.  The National Guidelines Clearinghouse has a very similar recommendation for the use of videofluoroscopy in whiplash associated disorders.  We who do the DMX studies think that 30-40 days after the MVC, a reasonably good motion study can be done.  But even though I try to let everyone I visit about the DMX machine know that motion studies are problematic in the newly injured spine, every now and then, I get a referral of a case which occurred only ten days to two weeks earlier.  And I get it- it’s a good thing to know early on if the alar ligaments are intact or not.  But most of the time, there is obvious decreased ROM in any combination of parameters which hinders the results of the test.  I always write the report, noting the diminished ROM, and request that the patient return in one month for a follow-up, complete motion study (no extra charge), at which time I will write an addendum to the original study.  But only rarely have I seen a patient for a follow-up study, which I think opens me up for criticism.

This article shows why DMX studies are not definitive at two weeks after the MVC.  There is usually still some residual muscle guarding which limits the motion enough to hide potentially seriously unstable segments.  Missing occult ligamentous instability can have catastrophic results, so it’s important to do the study correctly, the first time, or at least get a full, follow-up study at a time that satisfies the standards of the ACCR.  One has to wonder just how many ligament injuries were missed by the authors of the study because they didn’t flag anyone who did not exceed 3.5 mm. in anterolisthesis or retrolisthesis.  110 of the 1,451 patients included in the study exceeded the White-Panjabi standard, which is roughly 7% of the study population who had grade 3 sprains which needed surgical solutions.  There is no mention of the outcome of the patients in the study who had grade I or grade II ligament damage.  At any rate, it is our job as chiropractic clinicians to identify the damage, and to do that, you need properly done digital motion x-ray studies.