Fig. 1

Example graph depicting relative rotation in motion segments in the lower cervical spine during extension movement in C4-C7, in an asymptomatic subject. Sagittal rotation (‘Rotation’, y-axis) of the individual motion segments of the lower cervical spine, set against cumulative sagittal rotation in the segment C4-C7 (i.e. the amount of extension in block C4-C7). The y-axis represents sagittal rotation (in degrees) of the individual motion segments of the lower cervical spine, while on the x-axis the cumulative sagittal rotation (in degrees) in C4-C7 is displayed. Peaks in the graphs depict maximum contributions of that motion segment. During the end of the extension movement the peak of C4-C5 (1) is followed by a peak in C5-C6 (2), and then C6-C7 (3) again. This last phase [1] is commonly found in extension in asymptomatic individuals (85%). Only the order of the peaks is important, not the height of the peaks on itself, except for very small peaks with a rotation lower than 0.3, which are deemed insignificant. In many cases there is a peak in C4-C5 at the end of extension, which is much smaller than the peak at (1), this is considered normal