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The aim of this study was to characterize cervical disc deformation in asymptomatic subjects and single-level arthrodesis patients during in vivo functional motion. A validated model-based tracking technique determined vertebral motion from biplane radiographs collected during dynamic flexion-extension. Level-dependent differences in disc compression-distraction and shear deformation were identified within the anterior and posterior annulus (PA) and the nucleus of 20 asymptomatic subjects and 15 arthrodesis patients using a mixed-model statistical analysis. In asymptomatic subjects, disc compression and shear deformation per degree of flexion-extension progressively decreased from C23 to C67. The anterior and PA experienced compression-distraction deformation of up to 20%, while the nucleus region was compressed between 0% (C67) and 12% (C23). Peak shear deformation ranged from 16% (at C67) to 33% (at C45). In the C5-C6 arthrodesis group, C45 discs were significantly less compressed than in the control group in all disc regions (all p ≤ 0.026). In the C6-C7 arthrodesis group, C56 discs were significantly less compressed than the control group in the nucleus (p = 0.023) and PA (p = 0.014), but not the anterior annulus (AA; p = 0.137). These results indicate in vivo disc deformation is level-dependent, and single-level anterior arthrodesis alters the compression-distraction deformation in the disc immediately superior to the arthrodesis.
Anderst et al. (Wed,) studied this question.