In vitro experiments using cadaveric cervical spine motion segments to quantify facet capsular ligament strain during whiplash-like loading.
To quantify facet capsule strains during whiplash-like loading with an axial intervertebral prerotation simulating an initial head-turned posture and to then compare these strains to previously-published strains for partial failure and gross failure of the facet capsule for these specimens.
Clinical data have shown that a head-turned posture at impact increases the severity and duration of whiplash-related symptoms.
Thirteen motion segments were used from 7 women donors (50 ± 10 years). Axial pretorques (±1.5 Nm), axial compressive preloads (45, 197, and 325 N), and quasi-static shear loads (posteriorly-directed horizontal forces from 0 to 135 N) were applied to the superior vertebral body to simulate whiplash kinematics with the head turned. Three-dimensional displacements of markers placed on the right facet capsular ligament were used to estimate the strain field in the ligament during loading. The effects of pretorque direction, compression, and posterior shear on motion segment motion and maximum principal strain in the capsule were examined using repeated-measures analyses of variance.
Axial pretorque affected peak capsule strains more than axial compression or posterior shear. Peak strains reached 34% ± 18% and were higher for pretorques toward rather than away from the facet capsule (i.e.—, head rotation to the right caused higher strain in the right facet capsule).
Compared to previously-reported data for these specimens, peak capsule strains with a pretorque were double those without a pretorque (17% ± 6%) and not significantly different from those at partial failure of the ligament (35% ± 21%). Thus a head-turned posture increases facet capsular ligament strain compared to a neutral head posture—a finding consistent with the greater symptom severity and duration observed in whiplash patients who have their head turned at impact.
Cervical motion segments were used to quantify facet capsule strain during simulated whiplash exposures with the head turned. Peak capsule strains with the head-turned were twice those previously reported with the head forward and were not significantly different from those previously reported to cause partial failures in the capsule ligament.
From the *MEA Forensic Engineers & Scientists, Richmond;. †School of Human Kinetics, University of British Columbia, Vancouver, BC, Canada; Departments of ‡Neurosurgery; §Bioengineering, University of Pennsylvania, Philadelphia, PA; ¶Department of Biomedical Engineering, Duke University, Durham, NC; ∥Japan Automobile Research Institute, Tsukuba, Ibaraki; and **Japan Automobile Manufacturers Association, Tokyo, Japan.
Acknowledgment date: August 21, 2007. Revision date: January 2, 2008. Acceptance date: February 4, 2008.
Supported by Japan Automobile Research Institute, US Department of Health and Human Services, Centers for Disease Control Grant R49/CCR402396–12, Catharine Sharpe Foundation, an International Society of Biomechanics Student Travel Grant, the Natural Science and Engineering Research Council, and the Science Council of British Columbia.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Corporate/Industry, Federal and Professional Organizational funds were received in support of this work. One or more of the author(s) has/have received or will receive benefits for personal use from a commercial party related directly or indirectly to the subject of this manuscript: e.g., honoraria, gifts, consultancies, royalties, stocks, stock options, decision making position.
Address correspondence and reprint requests to Dr. Gunter P. Siegmund, MEA Forensic Engineers & Scientists, 11-11151 Horseshoe Way, Richmond, BC, Canada, V7A 4S5; E-mail: firstname.lastname@example.org