Uncinate processes and Luschka joints influence the biomechanics of the cervical spine: Quantification using a finite element model of the C5‐C6 segment

Abstract

Summary: A fully three-dimensional finite element model of a C 5 X 6 motion segment of the human spine was developed and validated for the purpose of investigating the biomechanical significance of uncinate processes and Luschka joints. The original intact cervical model was modified to create two additional models. The first simulated the absence of Luschka joints by replacing the fissures with continuous annulus fibrosus and leaving the uncinate processes intact. The second model simulated a surgical resection of the uncinate processes, while leaving the Luschka joints intact. The results of these two models were compared with the intact model, which served as a baseline; thus, the relative contributions of these two structures to cervical motion were established. With use of our model, it was possible, for the first time, to provide quantitative data concerning the source of coupled motions in the lower cervical spine. In principle, the results from this model support the hypothesis of Penning and Wilmink. Our results indicate that the facet joints and Luschka joints are the major contributors to coupled motion in the lower cervical spine and that the uncinate processes effectively reduce motion coupling and primary cervical motion (motion in the same direction as load application), especially in response to axial rotation and lateral bending loads. Luschka joints appear to increase primary cervical motion, showing an effect on cervical motion opposite to that of the uncinate processes. Surgeons should be aware of the increase in motion accompanied by resection of the uncinate processes.The function of uncinate processes and Luschka joints in passive control of lower cervical motion has not been definitively clarified. Frykholm (9) suggested that the uncinate processes provide a means for the cervical spine to protect the brachial plexus, whereas Hall (13) theorized that they allow for rotational movement. Penning and Wilmink (20) hypothesized that the coupling motion observed in the cervical spine is not determined solely by the orientation of the facets. Rather, they suggested that the location and orientation of the uncinate processes are such that coupled motions in the lower cervical spine could be explained by their presence.The uncinate processes are bony protuberances that extend cranially from the lateral margins of the superior endplates in the lower cervical spine (Fig. 1). A unique feature of the cervical intervertebral disc is the presence of a fissure or cleft that runs along the uncinate process toward the nucleus pulposus. This fissure, called a Luschka or uncovertebral joint, appears in the Received October 28,1996; accepted March 15,1997. Address correspondence and reprint requests to V. K. Goel at Department of Biomedical Engineering, EB 1208, University of Iowa, Iowa City, 1A 52242, U.S.A. E-mail: Vijay-Goel@uiowa.edu annular lamellae, and the adjacent collagenous fibers reorient and run parallel with the fissure (9,13,14). Luschka joints appear in the latter part of the first decade of li...

Validation of a Finite Element Model of the Young Normal Lower Cervical Spine

“…Not all finite element models (FEMs) of the human cervical spine have been subjected to rigorous validation and therefore have limited application to the study of normal and abnormal cervical conditions. Detailed static models of the cervical spine have been developed by Saito et al, 42 Bozic et al, 2 Teo et al, 48 Voo et al, 51 Clausen et al, [5][6][7] Maurel et al, 35 Goel and Clausen, 18 Kumaresan et al,27,28,32 and Ng et al 38 Each of these models is limited by the degree of its conformity to appropriate geometry, material properties, boundary conditions, loading, and validation.…”

“…2,42,48 Other models used validation data that included degenerated specimens with normal specimens. [5][6][7]35,38 To study disc degeneration at a single spinal level it is important to have a model that includes three motion segments: the degenerated disc and normal discs above and below. The three-motion segment model allows the effects of single level degeneration on upper and lower segments to be measured.…”

Uncovertebral joint injury in cervical facet dislocation: the headphones sign

“…The importance of these uncovertebral joints in the stability of the cervical spine has been highlighted by Clausen and colleagues as major contributors in coupled motion along with the facet joints in response to axial rotation and lateral bending loads [10]. The joint allows an increase in the range of motion, while the uncinate processes act as stabilizers with respect to the motion of the cervical spinal segment [10].…”

“…The joint allows an increase in the range of motion, while the uncinate processes act as stabilizers with respect to the motion of the cervical spinal segment [10]. The close association of the facet joint and uncovertebral joint in cervical spine motion probably explains the association of uncovertebral dislocation with CFJD and thereby the positive uni-or bilateral headphones sign.…”

Posterior cervical fixation following laminectomy: a stress analysis of three techniques

“…Their insertion points were chosen to mimic anatomic observations as closely as possible [16,17]. Material and mechanical properties shown in Table 1 for each spinal component represented the most commonly used values obtained from the literature [18][19][20][21].…”