Cervical spine posteroanterior stiffness differs with neck position

Spinal stiffness is commonly considered when treating patients with neck pain, but there are few studies reporting the objective measurement of cervical spine stiffness or the possible kinesiological factors that may affect its quantification. The aim of this study was to determine if the position of the neck affects cervical spine stiffness.

An instrumented stiffness assessment device measured posteroanterior cervical spine stiffness at C4 of 25 prone-lying asymptomatic subjects in three neck positions in randomised order: maximal flexion, maximal extension, and neutral. The device applied five standardised mechanical oscillatory pressures while measuring the applied force and concurrent displacement, defining stiffness as the slope of the linear portion of the force-displacement curve. Repeated measures analysis of variance with Bonferroni-adjusted post hoc comparisons determined whether stiffness differed between neck positions.

There was a significant difference in cervical spine stiffness between different neck positions (F((1.6,38.0)) = 16.6, P < 0.001). Stiffness was least in extension with a mean of 3.09 N/mm (95% CI 2.59, 3.58) followed by neutral (3.94, 95% CI 3.49, 4.39), and then flexion (4.32, 95% CI 3.96, 4.69).

When assessing cervical spine stiffness, neck position should be standardised to ensure maximal reliability and utility of stiffness judgments.