Posteroanterior movements in tender and less tender locations of the cervical spine

In order to determine how posteroanterior movements (PAs) are related to tenderness and thus possibly symptom production, we measured PA movements to a force of 25 N on each side of the cervical spines of asymptomatic subjects. From 10 subjects (six females and four males; mean age 37.2, range 21–50), 10 locations with a difference in tenderness to pressure between sides were used for analysis. The force–displacement and stiffness–force curves for tender and control sides were compared in four ways: simultaneous confidence bands (SCBs) for each side; width of SCBs for each side; SCBs of the difference between pairs of the tender and control curves; and simultaneous prediction bands (SPBs) from the tender side were compared to individual curves of the controls. The tender side demonstrated greater variation of both displacement and stiffness. The tender sides demonstrated greater within-subject stiffness for all force levels above 12 N. All individual stiffness–force curves of the tender sides were significantly different from the control side. Expected differences in single measures of either displacement or stiffness were not detected. The results suggest that the pattern of stiffness is a more effective method of characterizing PA mobility than single measures used in previous studies.