Cervical spine joint loading with neck flexion.

Cervical spine flexion is a common posture for those using computers, tablets, and smartphones; the latter being dubbed 'text-neck' in recent years. Coincidentally, flexion has been flagged as a significant mechanical risk factor for the development of chronic neck pain. Unfortunately, few modelling endeavours have attempted to quantify the intervertebral joint loads throughout the cervical spine in flexion, while still accounting for muscular activation. Eight healthy male subjects undertook five trials beginning in a neutral posture, flexed to 45 degrees, and returned to a neutral posture. 3 D head-trunk angles and surface electromyography from 10 neck muscles (5 bilaterally) were used as inputs into an inverse dynamic cervical spine model based on a 50th percentile male to compute the compression and anteroposterior (AP) shear forces for this flexion task. In general, compression increases cranially to caudally throughout the cervical spine, but levels off at the C5-C6 level. Conversely, in a neutral posture, there is a constant 18 N of anterior shear at each joint level. Compression increased twofold throughout the cervical spine with flexion, whereas anterior shear increased fourfold in the upper cervical spine and dramatically decreased caudally. The dramatic change in joint kinetics provides some mechanical evidence for the role of posture and interplay with muscle activity in the development of chronic neck pain. Results from this study can reinforce the need for appropriate workstation and monitor configurations and support the increased loading hypothesised to occur in 'text neck' postures. Practitioner summary: The purpose of this investigation was to quantify the compression and shear forces in the neck in 45 degrees of flexion compared to neutral. Flexion increased compression throughout the cervical spine 1.6-fold compared to a neutral posture. In the upper cervical spine, AP-shear increased four-fold compared to neutral. Abbreviation: AP: anteroposterior.