Variability of MCID and PASS Thresholds in Anterior Cervical Discectomy and Fusion Literature

Study Design. Systematic review Objective. This study aims to evaluate the variability of minimum clinically important difference (MCID) and patient acceptable symptom state (PASS) thresholds in current anterior cervical discectomy and fusion (ACDF) literature. Summary of Background Data. Patient-reported outcome measures (PROMs) are increasingly emphasized in recent studies evaluating outcomes of ACDF. To distinguish clinically meaningful improvements in PROMs, thresholds such as MCID and PASS have been delineated. However, the variability of the MCID/PASS threshold values can significantly influence study outcomes, limit validity of the results, and complicate comparisons between studies. Methods. PubMed and Embase were queried for articles from Jan. 1, 2000 - May 1, 2024 reporting MCID or PASS values for PROMs following ACDF. Patient demographics, study characteristics, MCID/PASS thresholds, and threshold calculation methods were extracted for all PROMs. Results. A total of 55 studies were identified, including 16 unique PROMs reported. There were 231 MCID threshold values and 2 PASS threshold values included Of these, forty-seven studies referenced previously established values, while 6 studies calculated new thresholds. Among these 6 studies, 15 novel MCID thresholds and 1 novel PASS threshold were reported across 8 distinct PROMs. The ranges of MCID thresholds for the most common PROMs were 7.5-20 for NDI, 2.5-3.1 for VAS-neck, 2.5-4.6 for VAS-arm, 4.1-11.1 for SF-12 PCS, 4.7-9.7 for SF-12 MCS, and 4.5-8 for PROMIS-PF. Conclusion. There is a high degree of variability among MCID thresholds in the ACDF literature, especially for NDI, VAS-arm, SF-12 PCS, SF-12 MCS, and PROMIS-PF. Interestingly, threshold values may even vary among papers citing the same studies for their reference MCID thresholds, with previously calculated MCID thresholds being cited incorrectly in some cases. This study emphasizes the need for improved standardization of MCID threshold values in spine literature for more reliable and consistent assessments of surgical outcomes.