• Scott L Parker and Matthew J McGirt.
• Department of Neurosurgery, Vanderbilt University Medical Center, and Vanderbilt Spinal Column Surgical Quality and Outcomes Research Laboratory, Nashville, Tennessee.
• Neurosurgery. 2015 Mar 1; 76 Suppl 1: S64-70.

BackgroundMinimum clinical important difference (MCID) has been adopted as the smallest improvement in patient-reported outcome needed to achieve a level of improvement thought to be meaningful to patients.ObjectiveTo use a common MCID calculation method with a cost-utility threshold anchor to introduce the concept of minimum cost-effective difference (MCED).MethodsForty-five patients undergoing transforaminal lumbar interbody fusion for degenerative spondylolisthesis were included. Outcome questionnaires were administered before and 2 years after surgery. Total cost per quality-adjusted life-year (QALY) gained was calculated for each patient. MCED was determined from receiver-operating characteristic curve analysis with a cost-effective anchor of < $50,000/QALY and < $75,000/QALY. MCID was determined with the health transition item as the anchor.ResultsSignificant improvement was observed 2 years after transforaminal lumbar interbody fusion for all outcome measures. Mean total cost per QALY gained at 2 years was $42,854. MCED was greater than MCID for each outcome measure, meaning that a greater improvement was required to represent cost-effectiveness than a clinically meaningful improvement to patients. The area under the receiver-operating characteristic curve was consistently ≥ 0.70 with both cost-effective anchors, suggesting that outcome change scores were accurate predictors of cost-effectiveness. Mean cost per QALY gained was significantly lower for patients achieving compared with those not achieving an MCED in visual analog scale for leg pain ($43,560 vs $112,087), visual analog scale for back pain ($41,280 vs $129440), Oswestry Disability Index ($30,954 vs $121,750), and EuroQol 5D ($35800 vs $189412).ConclusionMCED serves as the smallest improvement in an outcome instrument that is associated with a cost-effective response to surgery. With the use of cost-effective anchor of < $50,000/QALY, MCED after transforaminal lumbar interbody fusion was 4 points for visual analog scale for low back pain, 3 points for visual analog scale for leg pain, 22 points for Oswestry Disability Index, and 0.31 QALYs for EuroQol 5D.

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