Psychometric evaluation of the Japanese neck disability index by exploratory factor analysis in preoperative patients with cervical spondylotic myelopathy: impact of pain and numbness

Abstract

BACKGROUND CONTEXTThe Neck Disability Index (NDI), a common Patient-Reported Outcome Measure (PROM) for neck pain, lacks sufficient study on its psychometric properties in preoperative patients with cervical spondylotic myelopathy (CSM). PURPOSEThis study aims to address these gaps by conducting an exploratory factor analysis of the Japanese NDI. The objectives are 2-fold: (1) to scrutinize the psychometric properties and internal consistency of the Japanese NDI, and (2) to explore the specific regions of pain and numbness influencing the NDI. STUDY DESIGN/SETTINGA single-center observational study. PATIENT SAMPLEA total of 100 preoperative patients with CSM. OUTCOME MEASURESThe NDI and Numerical Rating Scale (NRS) were employed to assess preoperative neck disability and pain and numbness in various body regions. METHODSDemographic and clinical characteristics were collected, encompassing age, sex, body mass index, American Society of Anesthesiologists classification, smoking status, comorbidities, pain and numbness at various sites using the NRS, and NDI. For evaluating the psychometric properties and internal consistency of the NDI, exploratory factor analysis (EFA) and Cronbach's α coefficient were utilized. Furthermore, the impact of pain and numbness on NDI factors was examined through multivariable regression analysis. RESULTSEFA identified 2 factors—Physical and Mental—highlighting the dual nature of neck-related disability. Physical factors (std.β=0.724, p<.001) exerted a stronger impact on NDI scores compared to Mental factors (std.β=0.409, p<.001). Cronbach's α coefficient was 0.831 for physical factors and 0.723 for mental factors, indicating a high level of internal consistency. Numbness in the hand (std.β=0.338, p<.001) and pain in the neck (std.β=0.202, p=.035) were significant variables influencing Physical factor, while numbness in the hand (std.β=0.485, p<.001) and pain in the head (std.β=0.374, p<.001) impacted Mental factor. CONCLUSIONThis study contributes valuable insights into the psychometric properties of the NDI in preoperative patients with CSM. The identified factors emphasize the importance of addressing both physical and sensory symptoms in preoperative care.