Cut-off values of and factors associated with a negative influence on Neck Disability Index

The Neck Disability Index (NDI) is used to evaluate patients with cervical spine disease. However, few reports have defined the cut-off values of the NDI. The purpose of this study was to identify the cut-off values of and factors with a negative impact on NDI.

A total of 487 volunteers were divided into three groups based on disability: none, mild, and disabled. The cut-off values of the NDI were determined using receiver-operating characteristic curves. After these groups were divided based on sex and age adjustment was performed, the factors with a negative impact on NDI were investigated using multiple logistic regression analysis.

Groups none, mild, and disabled included 207, 186, and 94 volunteers, respectively. The cut-off values of the NDI in each group were 0-5, 6-17, and ≥ 18%, respectively. After adjusting for age, groups none, mild, and disabled had 65, 56, and 23 males, respectively, and 92, 103, and 56 females, respectively. In multiple logistic regression analysis, the factors with a negative impact on NDI in males were manual work (odds ratio [OR] 1.924), higher T1 slope minus cervical lordosis (OR 1.043), and higher C2-7 sagittal vertical axis (OR 1.029, P < 0.05). Among females, the factors were hand-grip strength (OR 0.936), body fat percentage (OR 0.942), and sporting activity (OR 0.456, P < 0.05).

Deterioration in NDI was associated with cervical spinal malalignment and manual labor in males and lack of physical activity and sarcopenia in females. These slides can be retrieved under Electronic Supplementary Material.