Study design: Controlled laboratory study using a cross-sectional, repeated-measures design.
Objectives: To quantify maximal voluntary isometric neck forces in healthy subjects and individuals with whiplash-associated disorder (WAD), using an objective measurement system to evaluate the test-retest properties of these strength measurements and to assess the links between neck strength, pain, kinesiophobia, and catastrophizing in patients with WAD.
Background: The prognosis of WAD is difficult to predict due to a lack of objective measurement methods and to our limited understanding of the role of psychological factors in the development of chronic WAD symptoms.
Methods and measures: Fourteen subjects with chronic WAD grade I or II and an age-matched, healthy group (n = 28) participated in this study. Cervical strength was measured with the Multi-Cervical Unit (MCU) in 6 directions, and pain was measured with a visual analog scale. Individuals in the WAD group completed the Neck Disability Index (NDI), the Tampa Scale for Kinesiophobia (TSK), and the Pain Catastrophizing Scale (PCS).
Results: Significant deficits in strength were observed for the individuals in the WAD group compared to the healthy group, particularly in extension, retraction, and left lateral flexion (P<.05). The MCU demonstrated good intratester reliability for the healthy group (ICC = 0.80-0.92) and the WAD group (ICC = 0.85-0.98), and small standard errors of measurement for both groups. No significant association was found between neck strength and NDI, TSK, and PCS.
Conclusion: The MCU demonstrated good test-retest properties for healthy subjects and individuals with WAD. Cervical strength was lower in individuals with WAD; however, the strength deficits were not clearly linked with psychological factors.