A minimum clinically important difference (MCID) has been increasingly well known in the current era of patient-centered care because it reflects a smallest change that is meaningful for patients following a clinical intervention. Previous studies suggested MCID values are disease and/or procedure dependent. No MCID values have been reported on the lumbar spinal stenosis (LSS) following decompression surgery despite LSS is the most common spinal disease and the main treatment is decompression surgery. Therefore, this study aimed to determine the MCID values as major outcome measures including the Numeric Rating Scale (NRS) of back pain, leg pain and numbness, Roland-Morris Disability Questionnaire (RMDQ), and Physical Component Summary (PCS) and Mental Component Summary (MCS) of Short Form 8 (SF-8) for patients with LSS undergoing decompression surgery.
This is a retrospective cohort study using prospectively collected data from consecutive patients who underwent lumbar decompression without fusion for LSS at a single institution between May 2014 and March 2016. Inclusion criteria were 1) minimum 1-year follow-up 2) a complete set of preoperative and final follow-up questionnaires available, including the NRS, RMDQ, and SF-8. Revision surgery or non-degenerative etiology such as infection or tumor was excluded. MCIDs of each outcome measure were determined using two major approaches, distribution- and anchor-based methods. The distribution-based method uses the distributional characteristics of the sample. This method expresses the observed degree of variation to obtain a standardized metric such as the standard deviation or standard error of measurement. The anchor-based method uses an external criterion known as anchor to determine the factors that should be considered by patients for an important improvement. Anchor-based methods assess how much changes in the measurement instrument correspond with a minimal important change defined on the anchor. We used symptom severity, physical function, and satisfaction scores from Zurich Claudication Questionnaire as anchors for NRS and RMDQ, PCS, and MCS, respectively.
A total of 126 patients were included. From the anchor-based method, MCIDs were determined to be 2 points for back pain, 4 points for leg pain and numbness, 5 points for RMDQ, 5 points for PCS, and 2 points for MCS. From the distribution-based method, MCIDs were determined to be 2 points for back pain, leg pain and numbness, 3-4 points for RMDQ, 6 points for PCS, and 5 points for MCS.
We first identified the MCIDs of the NRS, RMDQ, and SF-8 specific to patients undergoing decompression surgery for LSS.

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