Range of global motion of the cervical spine: intraindividual reliability and the influence of measurement device.

Range of motion tests are often employed in the quantification of musculoskeletal impairment and in the assessment of the efficacy of therapeutic interventions. The aim of the present study was to compare the absolute values for, and the day-to-day reliability of, measures of cervical spinal mobility made with two computerised motion analysis devices. The ranges of cervical flexion, extension, lateral bending, axial rotation, and axial rotation in flexion and extension were determined for 19 volunteers using both the CA6000 Spine Motion Analyser and the Zebris CMS system; all measures were repeated on a second occasion 1-3 days later. The test-retest reliability was good for each instrument: there was no significant difference between the mean values derived on the two separate days (P>0.05), and the corresponding intraclass correlation coefficients were 0.75-0.93 for all pri-O mary movements and 0.57-0.93 for axial rotation in flexion or in extension. For each primary movement, a small but significant difference (1-10%; P<0.05) between the values derived from the two instruments was observed, the systematic nature of which was revealed by the excellent correlation coefficients between them. For the measures of axial rotation in flexion or in extension, however, there was not only a poor correlation between the data obtained from the two devices, but the mean values also differed significantly. Each device is highly reliable in itself and can be used with confidence in longitudinal studies. The establishment of 'normal' values for the primary motions should take account of the slight differences observed between devices. Normal values for rotation in flexion or extension cannot be established until the source of the device-dependent difference is identified.