Cervical facet joint kinematics during bilateral facet dislocation

Abstract

Previous biomechanical models of cervical bilateral facet dislocation (BFD) are limited to quasi-static loading or manual ligament transection. The goal of the present study was to determine the facet joint kinematics during high-speed BFD. Dislocation was simulated using ten cervical functional spinal units with muscle force replication by frontal impact of the lower vertebra, tilted posteriorly by 42.5°. Average peak rotations and anterior sliding (displacement of upper articulating facet surface along the lower), separation and compression (displacement of upper facet away from and towards the lower), and lateral shear were determined at the anterior and posterior edges of the right and left facets and statistically compared (P < 0.05). First, peak facet separation occurred, and was significantly greater at the left posterior facet edge, as compared to the anterior edges. Next, peak flexion rotation and anterior facet sliding occurred, followed by peak facet compression. The highest average facet translation peaks were 22.0 mm for anterior sliding, 7.9 mm for separation, 9.9 mm for compression and 3.6 mm for lateral shear. The highest average rotation of 63°occurred in flexion, significantly greater than all other directions. These events occurred, on average, within 0.29 s following impact. During BFD, the main sagittal motions included facet separation, flexion rotation, anterior sliding, followed by compression, however, non-sagittal motions also existed. These motions indicated that unilateral dislocation may precede bilateral dislocation.

The effect of axial compression and distraction on cervical facet mechanics during anterior shear, flexion, axial rotation, and lateral bending motions

“…However, motion segments do not exhibit physiological kinematics during cervical trauma (Ivancic et al, 2008;Nightingale et al, 1996;Nightingale et al, 2016;Panjabi et al, 2007), and it is important to obtain quantitative information about the mechanical response of cervical FSUs and the facets during constrained intervertebral motions to develop improved injury tolerance levels. When extrapolating these results beyond physiological limits it is important to recognize that the quasi-static rates applied in this study were substantially slower than the ~3 m/s associated with head-impact loading causing cervical injury (McElhaney et al, 1979;Nightingale et al, 1996;Van Toen et al, 2014).…”

“…Such muscle forces may impose an additional intervertebral compressive load during injury that restricts traumatic flexion and intervertebral separation, causing increased loading of the facets. In contrast, superimposed intervertebral distraction during traumatic cervical motion, such as that observed during inertially-produced CFD (Ivancic et al, 2008;Panjabi et al, 2007), may reduce loading of the facets, thereby reducing the likelihood of concomitant facet fracture.…”

Mechanisms of cervical spine injury in rugby union: is it premature to abandon hyperflexion as the main mechanism underpinning injury?

“…Hyperflexion is characterised by forward motion of the head, beyond normal craniocervical range (often with the jaw contacting the torso) as shown in figure 1A during scrum engagement and in figure 2A, and is caused by posterior to anterior forces on the head. This mechanism has been shown, in ex vivo spine investigations to result in facet joint contact and ramping of the superior facet up the inferior facet which results in distraction and flexion of the intervertebral joint and, ultimately, facet dislocation38–40 and it is clearly present for forward players in the scrum.…”

“…Ivancic et al 38 39 and Panjabi et al 40 have shown that flexion moments combined with axial compression and anterior shear forces (like those during scrum and causing hyperflexion) can result in facet dislocations in the lower cervical spine. In fact, several factors like the angle of head impact, initial neck posture and head constraint are all relevant to cervical spine injury from head-first impact.…”

Three-dimensional motion analysis of the cervical spine for comparison of anterior cervical decompression and fusion versus artificial disc replacement in 17 patients

“…In recent years, articular facet biomechanics has become a topic of interest, [29][30][31][32]44,52 as significant changes in relative facet motion following trauma or surgery have been suggested to induce degenerative changes in the articular cartilage. 55,65 Although studies have investigated in vivo facet kinematics at the lumbar spine, 40,44 there are no known in vivo studies that have compared different surgical techniques on facet kinematics in the cervical spine.…”