VAS and NRS, Same or Different? Are Visual Analog Scale Values and Numerical Rating Scale Equally Viable Tools for Assessing Patients after Microdiscectomy?

Abstract

Objectives. To compare the viability of the numerical rating scale (NRS) and the visual analogue scale (VAS) as a pain assessment tools among a large cohort of patients who underwent microdiscectomy. Summary of Background Data. The pain intensity (PI) reduction is a parameter of surgical treatment efficacy. The two most commonly used scales of PI are NRS and VAS. Many studies have shown strong similarities between those two scales, but the direct interchange is difficult. Methods. Patients, who underwent microdiscectomy, were prospectively enrolled into the study and assessed using VAS and NRS for the back (NRS-B) and the leg (NRS-L), Short Form of McGill Pain Questionnaire (SF-MPQ) included Pain Rating Index (PRI) and Oswestry Disability Index (ODI) 1 day before and 1 month and 3 months after the procedure. Results. 131 patients were included in the study. NRS-L, NRS-B, VAS, and ODI were significantly lower ( $p<0.001$ ) 1 month after microdiscectomy. NRS-L and NRS-B ratings remained at a similar level while VAS and ODI decreased after 3 months. The rate of decline of PI measured by NRS-L correlated statistically significant (rs = 0.366; $p<0.001$ ) with ODI 1 month after surgery. Before surgery, the most significant correlation was found between ODI and NRS-L (rs = 0.494; $p<0.001$ ), the lowest with NRS-B (rs = 0.319; $p<0.001$ ). 3 months after surgery, there was higher correlations between ODI and VAS (rs = 0.634) than NRS-L (rs = 0.265). PRI correlated significantly ( $p<0.001$ ) and more stronger with VAS than with NRS-L and NRS-B in every points of assessment. Conclusion. The results showed that PI measurements by NRS-L/NRS-B and VAS mutually correlate and impair functionality evaluated by ODI (convergent validity) but in different modes (differential validity). NRS and VAS are not parallel scales and assess different aspects of pain. The measurement of NRS-L 1 month after microdiscectomy seems to give quick insight into the effectiveness of the procedure.