• Weishi Li, Shaobai Wang, Qun Xia, Peter Passias, Michal Kozanek, Kirkham Wood, and Guoan Li.
• Bioengineering Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital/Harvard Medical School, Boston, MA, USA.
• Spine. 2011 May 1;36(10):E629-37.

Study DesignControlled laboratory study.ObjectiveTo evaluate the effect of lumbar degenerative disc diseases (DDDs) on motion of the facet joints during functional weight-bearing activities.Summary Of Background DataIt has been suggested that DDD adversely affects the biomechanical behavior of the facet joints. Altered facet joint motion, in turn, has been thought to associate with various types of lumbar spine pathology including facet degeneration, neural impingement, and DDD progression. However, to date, no data have been reported on the motion patterns of the lumbar facet joint in DDD patients.MethodsTen symptomatic patients of DDD at L4-S1 were studied. Each participant underwent magnetic resonance images to obtain three-dimensional models of the lumbar vertebrae (L2-S1) and dual fluoroscopic imaging during three characteristic trunk motions: left-right torsion, left-right bending, and flexion-extension. In vivo positions of the vertebrae were reproduced by matching the three-dimensional models of the vertebrae to their outlines on the fluoroscopic images. The kinematics of the facet joints and the ranges of motion (ROMs) were compared with a group of healthy participants reported in a previous study.ResultsIn facet joints of the DDD patients, there was no predominant axis of rotation and no difference in ROMs was found between the different levels. During left-right torsion, the ROMs were similar between the DDD patients and the healthy participants. During left-right bending, the rotation around mediolateral axis at L4-L5, in the DDD patients, was significantly larger than that of the healthy participants. During flexion-extension, the rotations around anterioposterior axis at L4-L5 and around craniocaudal axis at the adjacent level (L3-L4), in the DDD patients, were also significantly larger, whereas the rotation around mediolateral axis at both L2-L3 and L3-L4 levels in the DDD patients were significantly smaller than those of the healthy participants.ConclusionDDD alters the ROMs of the facet joints. The rotations can increase significantly not only at the DDD levels but also at their adjacent levels when compared to those of the healthy participants. The increase in rotations did not occur around the primary rotation axis of the torso motion but around the coupled axes. This hypermobility in coupled rotations might imply a biomechanical mechanism related to DDD.

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