Neck Disability Index Scores of ≤7 Are Correlated with Patient Satisfaction Following Surgery for Degenerative Cervical Disc Disease

Comments by Ronald H.M.A. Bartels, MD, PhD

Successful senior man looking at reports while sitting on bed in rehab centerA study designed to correlate Neck Disability Index (NDI) score with patient satisfaction following anterior surgery for degenerative cervical disc disease found that an NDI cutoff of ≤7 corresponded to a good outcome as rated by patients, according to a report in PLoS One.

“NDI is an important measurement tool to evaluate the outcome of treatments related to neck-related pain syndromes,” explained senior author Ronald H.M.A. Bartels, MD, PhD, who is Professor and Chair of Department of Neurosurgery at Radboud University Medical Center in Nijmegen, The Netherlands.

“To evaluate the success of a treatment, the difference before and after the treatment is measured, and ideally this difference reaches a minimal clinically important difference,” said Dr. Bartels, who also is President of the Cervical Spine Research Society-Europe (CSRS-E). “However, an overt success does not mean that the patient is satisfied with the result, because the end result can still be an NDI with an unsatisfied patient.”

“A clear cut off value has never been estimated and validated,” Dr. Bartels said. “Therefore, we correlated the outcome after a frequently performed procedure (anterior cervical discectomy without fusion, with fusion by cage stand-alone or with disc prosthesis) with the outcome rated by the patient on a five-point Likert scale. A clear cut-off was established: In NDI ≤7 the patients said they have good to excellent result, otherwise they had a less than good result.”

The study involved 140 patients who underwent anterior surgery for treatment of symptomatic single level degenerative cervical disc disease and completed the NDI. The mean time after surgery to completion of NDI was 9.1 years. One month later, the patients were asked to qualify their clinical situation using a five-item Likert scale varying from excellent to bad. A total of 102 consecutive patients completed the questionnaire and were included in the analysis.

The investigators built a receiver operating characteristic (ROC) curve and calculated the area under the curve to estimate the best dichotomization in qualification of the clinical situation. The results showed that an NDI cutoff of ≤7 corresponded with the best dichotomized outcome, with a sensitivity of 81.08% and specificity of 78.57%.
NDI Score ChartFigure (above). Receiver operating characteristic (ROC) curve illustrating that an NDI of ≤7 is the cutoff value with the highest sensitivity and specificity for a good outcome as rated by patients. Reprinted from Donk et al. doi:10.1371/journal.pone.0161593.g002

NDI May Help Inform Patient Decision Making
“The cutoff value has been calculated based on the information provided by patients. Patients can determine which treatment they prefer after comparing the percentage of good outcome per offered treatment,” Dr. Bartels concluded.

“It is extremely important to emphasize the clinical relevance in each report of a study, but also in meta-analyses,” Dr. Bartels added. “The attention for clinical relevance is increasing, but in literature and at meetings, the focus is still on statistical relevance (P-value hunt).”

Updated on: 10/11/16
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