October 2001

In Whiplash, The Spine forms an S-Shaped Position

Whiplash is an acceleration-deceleration mechanism of energy transfer to the head and neck which can result in whiplash injury, bony and soft tissue injuries, and subsequently cause whiplash associated disorders or the clinical signs and symptoms that are patients present with following whiplash.1  Controversial have been the biomechanical mechanisms to explain zygapophyseal joint pain, the most common source of post-traumatic neck pain.2,3 

            Since the Quebec Task Force guidelines have appeared, numerous studies have now appeared that provide the missing link to the actual mechanisms of injury in whiplash.

In Whiplash, The Neck Forms a Sigmoid Configuration.

            In pursuit of the injury mechanism, bioengineers have used mathematical modeling, cadaver studies, and human volunteers to study the kinematics of the neck under the conditions of whiplash.4 Particularly illuminating have been cinephotographic and cineradiographic studies of cadavers and of normal volunteers that have appeared quite recently.                          In 1997, Grauer’s group (including Panjabi & Dvorak) published their work in crash testing with cadaver specimens.5  In this work they found that during the first 100 ms of whiplash the neck forms an “S” shaped curvature causing an opening of the anterior disc and impaction of the facet joints (Figure 1).

            In 1998, Kaneoka et al.6 performed cineradiography on 10 volunteer subjects who were strapped into a crash sled and slammed into a damper.  Each vertebra’s rotational angle and the instantaneous axes of rotation of the C5-C6 motion segments were quantified during the impact using cineradiography.  Their results demonstrated an upward shift in the instantaneous axis of rotation (IAR), very early in whiplash (100 ms) causing impaction of the facet joints and stretching of the disc as the spine took on a sigmoid configuration.  These authors revealed what Grauer et al. demonstrated in cadavers in vivo that the injury causing stage was when the cervical spine formed an S-shape.

            The exclamation point on this exciting trend in the literature is captured in the words of Bogduk, “the study of Kaneoka et al now fills a critical gap in the story of cervical facet pain. It provides the missing biomechanical link. Theirs is the most significant advance in the biomechanics of whiplash since the pioneering studies of Severy et al in 1955.  As a result of this study, we no longer rely on inference or speculation; we have a direct demonstration of the mechanism of injury in whiplash.”7

            This trend in the literature is further reiterated in research published in 2001.  In the June 1, 2001 issue of the journal Spine, comes another study corroborating the results of the findings in the previous studies.  Cusick et al.8 used high-resolution digital video to track the motions of individual facet joints as intact human cadaver head-neck complexes underwent inertia-type rear-end impacts.  Localized angular motion changes at each vertebral segment were analyzed to quantify the abnormal curvature changes.  The spine initially assumed an S-curve, with the upper spinal levels in flexion and the lower spinal levels in extension (Figure 2).

In Whiplash, the neck forms an "s"

            The authors concluded that these dynamic alterations of the upper level (occiput to C2) could impart potentially adverse forces to related neural structures, with subsequent development of a neuropathic pain process. The pinching of the lower facet joints may lead to potential for local tissue injury and nociceptive pain.

            Also in 2001, Eck et al.9 also recently stated in the American Journal of Medicine, “The most common radiographic findings include either preexisting degenerative changes or a slight flattening of the normal lordotic curvature of the cervical spine. Biomechanics studies have determined that after rear impact C6 is rotated back into extension before movement of the upper cervical vertebrae. Thus, the lower cervical vertebrae were in extension while the upper vertebrae were in a position of relative flexion, producing an S shape in the cervical spine. It is believed that this abnormal motion pattern might play a role in the development of whiplash injuries.”

            Lastly, as recent as the October 1, 2001 issue of Spine, another bioengineering article appears that demonstrates zygapophyseal joint injuries during whiplash.  Discussing their results, Siegmund et al.10 state, “The cervical facet capsular ligaments may be injured under whiplash-like loads of combined shear, bending, and compression. The results provide a mechanical basis for injury caused by whiplash loading. 

            The results of the present study provide a biomechanical basis for suggesting that facet capsular ligament injury plays a role in the pathoanatomy of the whiplash syndrome.”

            In the May, 2001 issue of the journal, Clinical Biomechanics, Bogduk & Yoganandan4 summarize this body of knowledge in regard to the latest evidence that we have available today coordinating injury mechanisms with patient clinical status. They state, “During this deformation, lower cervical segments undergo posterior rotation around an abnormally high axis of rotation, resulting in abnormal separation of the anterior elements of the cervical spine, and impaction of the zygapophyseal joints.                                        The demonstration of a mechanism for injury of the zygapophyseal joints complements postmortem studies that reveal lesions in these joints, and clinical studies that have demonstrated that zyga-pophysial joint pain is the single most common basis for chronic neck pain after injury.”4

Clinical Relevance

            As I end this article, I’d like to leave you with clinically relevant points to be gleaned from this important and exciting new research.

            • Whiplash injuries injure joints, discoligamenous structures, who’s avascular nature make them inherently slow to heal.

            • Stimulation of nociceptive afferents from the injury, the resultant inflammation, and/or abnormal loads placed upon the joints is the most likely pain generator.  Appropriate treatment, therefore should target the cause, the joints.

            • These injury mechanism provides an explanation why a significant portion of whiplash victims suffer prolonged and/or residual symptoms.11-13

References

1.         Spitzer WO, Skovron ML, Salmi LR et al. Scientific monograph of the Quebec Task Force on Whiplash-Associated Disorders: redefining “whiplash” and its management. Spine 1995;20:1S-73S.

2.         Lord SM, Barnsley L, Wallis BJ, Bogduk N. Chronic cervical zygapophyseal joint pain after whiplash. A placebo- controlled prevalence study. Spine 1996;21:1737-44.

3.         Barnsley L, Lord SM, Wallis BJ, Bogduk N. The prevalence of chronic cervical zygapophyseal joint pain after whiplash. Spine 1995;20:20-5.

4.         Bogduk N, Yoganandan N. Biomechanics of the cervical spine Part 3: minor injuries. Clin Biomech 2001;16:267-75.

5.         Grauer JN, Panjabi MM, Cholewicki J, Nibu K, Dvorak J. Whiplash produces an S-shaped curvature of the neck with hyperextension at lower levels. Spine 1997;22:2489-94.

6.         Kaneoka K, Ono K, Inami S, Hayashi K. Motion analysis of cervical vertebrae during whiplash loading. Spine 1999;24:763-9.

7.         Bogduk N. Point of View. Spine 1999;24:771.

8.         Cusick JF, Pintar FA, Yoganandan N. Whiplash syndrome: kinematic factors influencing pain patterns. Spine 2001;26:1252-8.

9.         Eck JC, Hodges SD, Humphreys SC. Whiplash: a review of a commonly misunderstood injury. Am J Med 2001;110:651-6.

10.       Siegmund GP, et al. Mechanical Evidence of Cervical Facet Capsule Injury During Whiplash: A Cadaveric Study Using Combined Shear, Compression, and Extension Loading. Spine 2001;26:2095-101.

11.       Suissa S, Harder S, Veilleux M. The relation between initial symptoms and signs and the prognosis of whiplash. Eur Spine J 2001;10:44-9.

12.       Carette S. Whiplash injury and chronic neck pain. N Engl J Med 1994;330:1083-4.

13.       Watkinson A, Gargan MF, Bannister GC. Prognostic factors in soft tissue injuries of the cervical spine. Injury 1991;22:307-9.