Three-dimensional movements of the upper cervical spine.

Knowledge of the normal movements of the occipito-atlanto-axial joint complex is important for evaluating clinical cases that may be potentially unstable. The purpose of this in vitro study was to quantitatively determine three dimensional movements of the occiput-C1 and C1-C2 joints. Ten fresh cadaveric whole cervical spine specimens (occiput to C7) were studied, using well-established techniques to document the movements in flexion, extension, left and right lateral bending, and left and right axial rotation. Pure moments of a maximum of 1.5 N-m were applied incrementally, and three-dimensional movements of the bones were recorded using stereophotogrammetry. Each moment was applied individually and in three load/unload cycles. The motion measurements were made on the third load cycle. Parameters of neutral zone, elastic zone, and range of motion were computed. Neutral zones for flexion/extension, right/left lateral bending, and right/left axial rotation were, respectively: 1.1, 1.5, and 1.6 (occiput-C1); and 3.2, 1.2, and 29.6 degrees (C1-C2). Ranges of motion for flexion, extension, lateral bending (one side), and axial rotation (one side) were, respectively: 3.5, 21.0, 5.5, and 7.2 degrees (occiput-C1 joint) and 11.5, 10.9, 6.7, and 38.9 degrees (C1-C2 joint). The greatest intervertebral motion in the spine was axial rotation at the C1-C2 joint, with the neutral zone constituting 75% of this motion.