Abstract
BackgroundThe 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.MethodsWire 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).ResultsAside 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.ConclusionThese 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.
Highlights
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
The cervical facet joints are a source of neck pain in about half of chronic whiplash patients [1]
Tendons of the cervical multifidus muscles insert directly onto the capsular ligaments [13,14] and it has been postulated that multifidus activation during the neuromuscular response to a rear-end automobile impact could increase the strain in the capsular ligaments above that imposed passively by the impactinduced head and neck dynamics [7,13]
Summary
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. The cervical facet capsule contains fine, unmyelinated nerves that likely have nociceptive function [11] Distending these ligaments by injection of contrast media has produced whiplash-like pain patterns in normal individuals [12]. Tendons of the cervical multifidus muscles insert directly onto the capsular ligaments [13,14] and it has been postulated that multifidus activation during the neuromuscular response to a rear-end automobile impact could increase the strain in the capsular ligaments above that imposed passively by the impactinduced head and neck dynamics [7,13]. Prior work has shown early multifidus activation during a whiplash response in one of three subjects [15], it remains unclear whether this reflex response will be present in a larger group of subjects
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