The objective of the present study is to determine to the three-dimensional segment-specific coupling factors from healthy, normal, non-degenerated human cervical spinal columns under bending. Using pure moment loading protocols, cadaver subaxial columns were fixed at the two ends, off-axis forces and moments were recorded using a distal six-axis load cell, and primary and secondary rotations were obtained as a function of applied moments, up to 2.0 Nm. Segmental bone mineral densities were determined using quantitated computed tomography (QCT). Coupling factors were the smallest at the cervico-thoracic spinal segment. Cranial and caudal decreases of the coupling factors occurred from the mid-cervical segment at all applied moment levels, from 65 to 72% at the C4-C5 segment and 59 to 75% at the C5-C6 segment. On average, 55% of the primary rotation was coupled with the secondary rotation across the entire column. Peak coupling occurring in these segments may indicate a greater propensity for age-related changes to these vertebral levels, and offer support to the commonly observed lower cervical degeneration in clinical studies.

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