Follow-up of degenerative lumbar spine surgery—PROMs stabilize after 1 year: an equivalence study based on Swespine data

Purpose To evaluate the outcome of degenerative lumbar spine surgery in a credible way, patient-reported outcome measures (PROMs) should be assessed after an adequate follow-up period. Most authors/journals consider a follow-up period of less than two years to be too short. The purpose of this study was to explore the possibility of restricting follow-up to one year. Methods Adult patients operated between 1998 and 2017 were retrieved from Swespine (Lumbar Disc Herniation n = 31,314, Lumbar Spinal Stenosis n = 53,043 and Degenerative Disc Disease n = 14,375). The proportion reaching the minimal important change (MIC) in Visual Analogue Scale for pain (VAS BACK/LEG ), Oswestry Disability Index (ODI) and the quality-of-life measure EQ-5D INDEX at 1 and 2 years, respectively, was calculated. The single-item questions such as Global Assessment (GA BACK/LEG ) and Satisfaction were analysed by the McNemar test. Threshold values for a successful outcome based on the final scores of each PROM at 1 and 2 years post-surgery were also defined. Results For all the three diagnostic groups, the differences in proportions reaching MIC of each PROM at 1 and 2 years were below 2%. Global Assessment and Satisfaction with outcome at one year remained at 2 years. There were no important differences of threshold values of treatment success based on final scores Conclusion No clinically important changes in PROMs appeared between 1 and 2 years after surgery for degenerative lumbar conditions, demonstrating that a follow-up period of 1 year as opposed to 2 years is sufficient in effectiveness studies if PROMs are to be used as outcome variables. Graphical abstract These slides can be retrieved under Electronic Supplementary Material.