The four-eye principle in preoperative indication for lumbar spine surgery: A retrospective cohort analysis with prospective follow-up.

Background: Accurate preoperative indication is crucial for achieving successful outcomes in lumbar spine surgery. The "four-eye principle," requiring consensus between two independent specialists, has been proposed as a quality assurance measure, yet clinical evidence and the potential impact of selection bias remain insufficiently explored. Methods: This monocentric retrospective cohort study with prospective follow-up included patients undergoing single-level TLIF or UD between 2010 and2020 at a DWG-certified spine center. Patients were allocated either to a control group (indication by a single spine surgeon) or a peer group (interdisciplinary four-eye principle involving a surgical and conservative specialist). PROMs (ODI, EQ-5D-5L, VAS back and leg pain) were recorded preoperatively and at 3, 12, and 24 months. Results were interpreted considering potential selection effects and surgeon variability. Results: A total of 166 patients were included (54 TLIF, 112 UD). In the TLIF cohort, the peer group demonstrated significantly greater improvements in ODI, EQ-5D, and VAS back pain at 12 and 24 months (p < 0.05). Differences in leg pain favored the peer group without statistical significance. In the UD cohort, outcomes were broadly comparable between groups. Interpretation is limited by inherent selection differences and potential variability in surgical performance. Conclusion: The four-eye principle was associated with superior functional and pain-related outcomes in patients undergoing lumbar fusion. While these findings suggest that structured, interdisciplinary indication processes may enhance patient selection, stricter thresholds for surgical approval and surgeon heterogeneity must be considered in interpreting the results. Prospective multicenter studies including non-operated patients are needed to validate the four-eye principle as a quality assurance tool.