The Variability of MCID, SCB, and PASS Thresholds in the Adult Spinal Deformity Literature

STUDY DESIGN: Systematic review. OBJECTIVE: We aimed to evaluate the variability in minimal clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptom state (PASS) thresholds utilized in the adult spinal deformity (ASD) literature. SUMMARY OF BACKGROUND DATA: Patient-reported outcome measures (PROMs) are increasingly employed to evaluate the outcomes in ASD patients. To distinguish clinically meaningful changes in numerical PROM values, thresholds such as MCID, SCB, and PASS have been developed. Yet, standardized thresholds for these metrics have not been established in the ASD population, potentially affecting clinical decision-making and outcome comparisons across studies. METHODS: PubMed and Embase were systematically searched for studies published from January 2000 to May 2024 that reported MCID, SCB, or PASS values following ASD surgery. Extracted data included patient demographics, study characteristics, reported threshold values, and threshold calculation methodologies. RESULTS: A total of 87 studies encompassing 23,553 ASD surgery patients were included (mean age: 59.3 y, BMI: 26.6). The most frequently reported PROMs were Oswestry Disability Index (ODI), Scoliosis Research Society-22 (SRS-22), Short Form-36 Physical Component Scale (SF-36 PCS). Overall, 371 MCID thresholds, 57 SCB thresholds, and 10 PASS thresholds were documented. Most studies (73/87) referenced previously established threshold values. Novel MCID thresholds were calculated in 14 studies, yielding 54 novel MCID thresholds for 24 different PROMs. The ranges of MCID thresholds reported were 6.8-36 for ODI, 3.3-7.83 for SF-36 PCS, 0.4-0.85 for SRS-22 Pain, and 0.4-1.6 for SRS-22 Appearance. The standard deviation of the SF-36 PCS SCB threshold (9.64) exceeded its mean value (9.4), underscoring extreme variability. CONCLUSION: MCID, SCB, and PASS threshold values in the ASD literature exhibit considerable variability, particularly among the most commonly used PROMs. Standardization of these thresholds specific to the ASD population is essential to enhance accuracy in outcome assessment, facilitate inter-study comparability, and improve clinical decision-making.