Trapped in the neutral zone: another symptom of whiplash-associated disorder?

Instability of the cervical spine following whiplash trauma has been demonstrated in a number of studies. We hypothesized that, in patients with whiplash-associated disorder, rotation of the head would be accompanied by an earlier onset of neck muscle activity to compensate for intrinsic instability. The aim of the study was to examine the range of motion (RoM) of the cervical spine and the onset and activity of the sternocleidomastoid (SCM) muscles during axial rotation, in healthy control subjects and in patients with chronic whiplash-associated disorder. Forty-eight control subjects (42% male) and 46 patients (33% male) with chronic whiplash-associated disorder (symptoms lasting longer than 3 months) were examined. Cervical axial RoM differed significantly (P = 0.0001) between the groups, with the whiplash patients showing lower values (83 degrees +/- 30 degrees) than the healthy controls (137 degrees +/- 19 degrees). The whiplash patient group showed no evidence of the predicted earlier activation of SCM muscles. Many patients never reached the point in the RoM where SCM muscle activity rises steeply, as it does in the healthy controls (the 'elastic zone'), and their movements remained mostly within the region of low muscle activity (the 'neutral zone'). The whiplash patients appeared either unable or unwilling to drive the cervical spine into this region of high muscle activity, possibly because they were restricted by existing pain or fear of pain.

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.