NDI

Abstract

Retrospective review of prospectively collected data. To determine the Neck Disability Index (NDI) cut-off for achieving patient acceptable symptom state (PASS) at six months following degenerative cervical spine surgery. An absolute score denoting PASS might be a better marker to assess clinical outcomes than a change score denoting minimal clinically important difference. Patients who underwent primary anterior cervical decompression and fusion, cervical disk replacement, or laminectomy were included. The outcome measure was NDI. The anchor used to assess PASS achievement at six months was the response on the Global Rating Change: "Compared with preoperative, you feel (1) much better, (2) slightly better, (3) same, (4) slightly worse, or (5) much worse." It was converted to a dichotomous outcome variable (acceptable=response of 1 or 2, unacceptable=response of 3, 4, or 5) for analyses. The overall cohort and subgroups based on age (65yr and below, above 65yr), sex, myelopathy, and preoperative NDI (≤40, >40) were analyzed for the proportion of patients achieving PASS and the NDI cut-off using receiver operator curve. Seventy-five patients (42 anterior cervical decompression and fusion, 23 cervical disc replacement, 10 laminectomy) were included. 79% of patients achieved PASS. Males, patients with age 65 years and below, preoperative NDI ≤40, and absence of myelopathy were more likely to achieve PASS. The receiver operator curve analysis revealed an Oswestry Disability Index cut-off of 21 to achieve PASS (area under the curve, AUC: 0.829, sensitivity: 81%, specificity: 80%). The subgroup analyses based on age, sex, myelopathy, and preoperative NDI revealed AUCs >0.7 and NDI threshold values consistent between 17 and 23. With an AUC of 0.829, NDI showed an excellent discriminative ability. Patients with NDI ≤21 are expected to achieve PASS following degenerative cervical spine surgery.