Responsiveness of Commonly Used Patient-Reported Outcome Instruments in Lumbar Microdiscectomy

STUDY DESIGN: Prospective observational cohort study. PURPOSE: To evaluate the comparative responsiveness of Oswestry Disability Index (ODI, version 2.0), 24-item Roland-Morris Disability Questionnaire (RMDQ), 12-item Short-Form Health Survey (SF-12) physical component score (PCS), and SF-12 mental component score (MCS) in patients that underwent micro-discectomy for lumbar disc herniation. OVERVIEW OF LITERATURE: Responsiveness is a context specific term and no study has reported the responsiveness of ODI version 2.0, RMDQ, SF-12 PCS, or SF-12 MCS in discectomy patients. METHODS: Responsiveness was assessed using distribution-based methods (effect size [ES], standardized response means [SRM ], SRM difference between patients who improved and those who did not show improvement [SRM difference]), and the anchor-based method (area under the curve [AUC] of receiver operating characteristic curves). Values of ES and SRM higher than 0.8, and AUC value higher than 0.7 suggest adequate responsiveness. Outcome instrument demonstrating the highest value of SRM difference and AUC was considered the most responsive. RESULTS: Responsiveness was assessed in 98 participants at a mean follow-up time of 12 weeks postoperatively. The overall ES of RMDQ, ODI, SF-12 PCS, and SF-12 MCS was 2.15, 2.11, 2.08, and 0.86, respectively. The overall SRM of ODI, RMDQ, SF-12 PCS, and SF-12 MCS was 1.36, 1.43, 1.24, and 0.65, respectively. The SRM difference in RMDQ, ODI, SF-12 PCS, and SF-12 MCS was 2.64, 2.26, 1.32, and 1.29, respectively. The AUC of ODI, RMDQ, SF-12 PCS, and SF-12 MCS was 0.96, 0.96, 0.83, and 0.83, respectively. CONCLUSIONS: ODI, RMDQ, SF-12 PCS, and SF-12 MCS demonstrated adequate responsiveness in a homogenous cohort of patients who underwent lumbar micro-discectomy. ODI and RMDQ are equally responsive and, thus, are interchangeable instruments for region specific outcomes. Both the SF-12 PCS and SF-12 MCS can assess the quality of life following lumbar micro-discectomy.