The assessment of clinically significant differences in treating spinal deformity using the SRS questionnaire: What is the threshold of change that is meaningful to patients?

Background: The measurement of health-related quality of life is important in spinal deformity surgery. The Scoliosis Research Society questionnaire has allowed disease-specific research in this area, and determining the minimal clinically important difference (MCID) is as important as it is elusive. We seek to further refine our estimations of clinically perceived improvements by the patient. Methods: We used an anchor-based approach for each domain of the SRS questionnaire to compare changes at 1 year after treatment. We set the MCID as the upper 95% boundary of the "no change" group bordering the "improvement" arm, where the patients may start to perceive their own change toward the better. We compared this with the mean change. Results: The threshold value for the MCID was 0.54 for the pain domain, 0.31 for function, 0.62 for self-image, and 0.5 for mental health. The mean changes in our group's pain and self-image exceeded their MCID. Conclusions: Compared with our previous work, we further attempted to refine our assessment of the MCID in spinal deformity. Pain continues to show clinically significant improvement, and self-image also demonstrated mean improvement over its estimated MCID. Level of Evidence: 2 Clinical Relevance: This result in self-image is an important addition to the MCID literature, given its lack of consistency in previous work.