Failure to Follow-Up in 41% of MCGR Patients: A Multi-Center Analysis of Prolonged Intervals and Associated Institutional Resources

Background: Magnetically controlled growing rods (MCGR) enable clinic-based distractions at prescribed intervals without surgery. No studies to date quantify failure-to-follow-up (FFU) for routine lengthenings or examine center-level characteristics associated with prolonged intervals. We hypothesize that an unrealized proportion of EOS patients will experience FFU and sought to define FFU rates across centers and explore site-level characteristics associated with FFU. Methods: A retrospective review of an international registry of EOS patients with at least 2 years of follow-up after implantation of MCGRs was conducted. FFU was predefined as >180 days between subsequent lengthenings, selected as a conservative, clinically meaningful threshold because routine MCGR distractions are typically performed more frequently (approximately every 2.5-3 months). Institutional variables not present in the base registry were obtained via a separate site-level questionnaire and analyzed among large-volume centers. Associations were interpreted as non-causal. Results: A median of 41% of patients experienced at least one FFU event, with frequency ranging from 0 to 80%. Three centers were determined to be outliers with a relatively high percent FFU (↑ FFU group), and two centers were high-performing outliers with a low FFU (↓ FFU group) rate. Centers that reported holding regular (≥monthly) spine research meetings demonstrated lower FFU rates, while other site-level variables showed mixed associations. Conclusions: FFU events were common in this multicenter cohort. Site-level characteristics showed associations with FFU frequency but do not imply causation. Future work should incorporate patient-level factors and prospective interval protocols to clarify determinants and outcomes of FFU. Key Concepts: (1) Over 40% of patients have at least one failure to follow-up event for magnetically controlled growing rod lengthening. (2) Institutional markers, such as research productivity, may be surrogates for infrastructural factors leading to increased failure to follow-up rates.