Psychological factors and domains of neck pain disability.

OBJECTIVE: This study evaluated the relationship between psychological distress and disability associated with neck pain, analyzed the Neck Disability Index (NDI) for disability factors, and assessed the impact of psychological distress on those domains of disability.
DESIGN: Prospective cross-sectional analytic survey.
SETTING: Outpatient physical therapy clinic. PATIENTS: Sixty-one consecutive adult subjects with dominant neck pain participated. OUTCOME MEASURES: Each subject completed the NDI, psychometric measures for the Distress Risk Assessment Method, and a numeric pain rating scale.
RESULTS: Measures of depression, somatization, and pain intensity explained 60% of the variance of disability due to neck pain. Factor analysis revealed two disability factors in the NDI dealing with physical activity/participation limitations and nonphysical activity-related impairments in bodily function. Psychological distress and pain intensity explained 25.6% of the variance of the factor dealing with activity/participation limitations, and 53.5% of the variance for the factor associated with impairments in bodily functions.
CONCLUSION: Nondistressed adults reported significantly less disability due to neck pain than psychologically distressed subjects. The NDI was found to contain two factors that pertain to three domains of the disability. Five items relating to impairments in bodily function strongly correlated with depression and somatization. Presence of psychological distress has a confounding effect on NDI scores. An outcome measure containing items related only to activity limitations and participation restrictions might give a truer picture of disability associated with neck pain for patients with psychological distress.