Inside-Out Versus Outside-In Transforaminal Endoscopic Lumbar Discectomy: A Structured Debate and International Practice Patterns

Transforaminal endoscopic lumbar discectomy (TELD) is performed by 2 techniques that differ in where the working corridor is first established: inside-out docks within the disc and works outward; outside-in establishes the corridor in the foramen, typically by foraminoplasty, and enters the disc last. This review tested each technique's arguments against the literature and described current expert opinion. The literature component was a narrative, nonsystematic structured debate across 7 domains, with one author arguing each position and a joint reconciliation assigning verdicts from a predefined taxonomy. A single-round structured international expert-opinion survey of 78 endoscopic spine surgeons from 23 countries was analyzed against a prespecified 70% agreement threshold. Seven domains yielded 8 verdicts because clinical outcomes were judged separately at short and long term: 2 resolved as mixed, 2 as context-dependent, 1 conditional on patient phenotype, and 3 unresolved for lack of comparative studies. The panel was imbalanced: 57.1% practiced predominantly outside-in and 6.5% predominantly inside-out. Ten statements met the threshold: acceptance of outside-in (85.9%; inside-out 43.6%), its preference in all 4 case scenarios and for foraminal or bony access, migrated fragments, annulus and nucleus preservation, and exiting-nerve safety, and neutrality on cost-effectiveness. Case 1 reached 70.1% among 77 decided respondents but 69.2% of the full panel of 78. Current evidence does not support a general recommendation for either technique, and the survey describes the preferences of a predominantly outside-in panel rather than establishing superiority. Selection should follow pathology, foraminal anatomy, and surgeon expertise.