The quantitative measurements of the intervertebral angulation and translation during cervical flexion and extension

The insufficient exploration of intervertebral translation during flexion and extension prevents the further understanding of the cervical biomechanics and treating the cervical related dysfunction. The objective of this study was to quantitatively measure the continuous intervertebral translation of healthy cervical spine during flexion and extension by videofluoroscopic technique. A total of 1,120 image sequences were analyzed for 56 healthy adult subjects by a precise image protocol during cervical flexion and extension. Our results showed there were no statistical angular differences among five spinal levels in either flexion or extension, except for the comparison between C2/3 (13.5 degrees) and C4/5 (22.6 degrees) angles. During cervical flexion, the smallest anterior translations were 0.7 mm at C2/3 level, followed by 0.9 mm at C6/7, 1.0 mm at C3/4, 1.1 mm at C5/6, and the largest 1.2 mm at C4/5 levels. The significantly greater translations were measured in the posterior direction at C3/4 (1.1 mm, P = 0.037), C4/5 (1.3 mm, P = 0.039), and C5/6 (1.2 mm, P = 0.005) levels than in the anterior one. The relatively fluctuant and small average posterior translation fashion at C6/7 level (0.4 mm) possibly originated from the variations in the direction of translation during cervical extension among subjects. Normalization with respect to the widths of individual vertebrae showed the total translation percentages relative to the adjacent vertebrae were 9.5, 13.7, 16.6, 15.0, and 8.6% for C2/3 to C6/7 levels, respectively, and appeared to be within the clinical-accepted ranges of translation in cervical spine. The intervertebral translations of cervical spine during flexion and extension movements were first described in quality and quantity based on the validated radiographic protocol. This analysis of the continuous intervertebral translations may be further employed to diagnose translation abnormalities like hypomobility or hypermobility and to monitor the treatment effect on cervical spines.