A Modified Delphi Consensus Study to Quantify Surgical Burden of Degenerative Lumbar Spinal Procedures: The Minimally Invasive Spine Surgery Invasiveness Classification “MISS-INC (L)”

Study Design Consensus-based classification development utilizing a modified Delphi process. Objectives To develop a practical, standardized classification system to quantify surgical invasiveness in minimally invasive degenerative lumbar spine procedures. Methods An international panel of 45 spine surgeons from the AO Spine Knowledge Forum – Degenerative participated in a three-stage, modified Delphi consensus process. First, candidate determinants of invasiveness were identified through evaluation of existing indices and literature review, then refined through iterative expert rounds. The scale was applied to standardized case scenarios, with internal review by the AO Spine Knowledge Forum – Degenerative and external review by the AO Spine MISS Task Force. Finally, a consensus survey reached ≥75% agreement on all final factors for inclusion in the grading scale. Results The final classification system included nine factors: operative time, number of approaches, blood loss, instrumentation, muscle dissection/access, anesthesia, number of levels, fusion technique, and revision status. Consensus was achieved on all components of the scale following iterative refinement. Each factor was scored from 0 (least invasive) to 2 (most invasive), generating a cumulative invasiveness score. Application of the scale across representative procedures demonstrated a spectrum ranging from least invasive (endoscopic 1-level discectomy) to most invasive (thoracic-to-pelvis fixation). Procedures were stratified into minimally invasive, less invasive, and more invasive categories. Conclusions MISS-INC (L) is a proposed, consensus-based classification that quantifies surgical invasiveness among minimally invasive lumbar spine procedures. It offers a user-friendly framework for communication, research, and patient counseling, with further validation against clinical outcomes representing an important next step.