Are cervical multifidus muscles active during whiplash and startle? An initial experimental study.
BACKGROUND
The cervical multifidus muscles insert onto the lower cervical facet capsular ligaments and the cervical facet joints are the source of pain in some chronic whiplash patients. Reflex activation of the multifidus muscle during a whiplash exposure could potentially contribute to injuring the facet capsular ligament. Our goal was to determine the onset latency and activation amplitude of the cervical multifidus muscles to a simulated rear-end collision and a loud acoustic stimuli.


METHODS
Wire electromyographic (EMG) electrodes were inserted unilaterally into the cervical multifidus muscles of 9 subjects (6M, 3F) at the C4 and C6 levels. Seated subjects were then exposed to a forward acceleration (peak acceleration 1.55 g, speed change 1.8 km/h) and a loud acoustic tone (124 dB, 40 ms, 1 kHz).


RESULTS
Aside from one female, all subjects exhibited multifidus activity after both stimuli (8 subjects at C4, 6 subjects at C6). Neither onset latencies nor EMG amplitude varied with stimulus type or spine level (p > 0.13). Onset latencies and amplitudes varied widely, with EMG activity appearing within 160 ms of stimulus onset (for at least one of the two stimuli) in 7 subjects.


CONCLUSIONS
These data indicate that the multifidus muscles of some individuals are active early enough to potentially increase the collision-induced loading of the facet capsular ligaments.
MEA Forensic Engineers & Scientists, Richmond, BC, Canada. gunter.siegmund@meaforensic.com
Gunter P
GP
Siegmund
Jean-Sébastien
JS
Blouin
Mark G
MG
Carpenter
John R
JR
Brault
J Timothy
JT
Inglis
D000054:Acceleration; D000161:Acoustic Stimulation; D000328:Adult; D002574:Cervical Vertebrae; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009334:Neck Muscles / Q000502:physiology*; D019547:Neck Pain / Q000209:etiology / Q000503:physiopathology; D012018:Reflex / Q000502:physiology*; D013216:Reflex, Startle / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology; D014911:Whiplash Injuries / Q000209:etiology / Q000503:physiopathology*