Variability of angular measurements of head posture within a session, within a day, and over a 7-day period in healthy participants

Head posture (HP) is used as part of the clinical examination of patients with neck pain to inform diagnosis, plan treatment, and monitor progress. For related information to be interpreted correctly, clinicians need to know how much of the variation in HP between measurements can be attributed to a change in the patient condition and how much is due to measurement error and/or biological variation. The aim of this study was to investigate the variability of angular measurements indicative of forward HP, head extension, and side flexion within a session, within a day, and over a 7-day period. Angles were calculated from 27 participants in three sessions over a period of 7 days through digitization of video images. Intraclass correlation coefficients (ICC) and standard error of measurement (SEM) showed that forward HP (ICC between 0.82 and 0.91; SEM between 1.42° and 1.70°) and side flexion (ICC between 0.63 and 0.85; SEM between 0.83° and 1.27°) were stable within a session, within a day, and over a 7-day period. Head extension was found to be less stable (ICC between 0.71 and 0.83; SEM between 2.69° and 3.72°). Time of day did not appear to influence forward HP, side flexion, or head extension.