UNCINATE PROCESSES AND LUSCHKA JOINTS INFLUENCE THE BIOMECHANICS OF THE CERVICAL-SPINE - QUANTIFICATION USING A FINITE-ELEMENT MODEL OF THEC5-C6 SEGMENT

A fully three-dimensional finite element model of a C5-C6 motion segme nt of the human spine was developed and validated for the purpose of i nvestigating the biomechanical significance of uncinate processes and Luschka joints, The original intact cervical model was modified to cre ate 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 su rgical 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 contribut ions of these mio structures to cervical motion were established, With use of our model, it was possible, for the first time, to provide qua ntitative data concerning the source of coupled motions in the lower c ervical spine. Zn principle, the results from this model support the h ypothesis 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 effective ly reduce motion coupling and primary cervical motion (motion in the s ame direction as load application), especially in response to axial ro tation and lateral bending loads. Luschka joints appear to increase pr imary cervical motion, showing an effect on cervical motion opposite t o that of the uncinate processes. Surgeons should be aware of the incr ease in motion accompanied by resection of the uncinate processes.