Comparison of Lateral Decubitus versus Prone Lateral Lumbar Interbody Fusion Using Impact Scores: A Method to Quantify Intraoperative Supply Cost and Variability in Surgery.

BACKGROUND CONTEXT: Surgical value metrics report intraoperative supply costs as aggregate institutional dollars, which do not identify which supply categories drive cost.

PURPOSE: To introduce the Impact Score, each supply category's percentage share of total intraoperative supply cost, as a descriptive framework and, using lateral decubitus (LD-LIF) versus prone lateral (PL-LIF) lateral lumbar interbody fusion as a proof of concept, to determine whether impact scores differ by supply category and align with median-cost rankings, whether exploratory outcome-based value metrics differ between approaches, and whether meaningful inter-surgeon variability exists.

PATIENT SAMPLE: Seventy-eight single-level L4-5 lateral lumbar interbody fusion cases performed from 2021 to 2026 (32 LD-LIF, 46 PL-LIF).

OUTCOME MEASURES: Category-level impact score (percentage of total intraoperative supply cost), supply and total intraoperative cost, exploratory value metrics based on the Oswestry Disability Index and PROMIS-10-derived quality-adjusted life years (including the operative value index and unit price per outcome), and 90-day readmission.

METHODS: Itemized intraoperative supply records were mapped to 33 standardized categories, and each category's impact score was computed as its percentage of total intraoperative supply cost. Time-driven activity-based costing provided staff costs. Category-level impact scores and costs were compared with unadjusted Wilcoxon rank-sum tests.

RESULTS: Impact-score and median-cost rankings were broadly concordant. LD-LIF showed higher impact for interbody, screw, biologic, and retractor/dilator, and PL-LIF for neuromonitoring and positioning (all p < 0.01). Navigation and rod did not differ. Total intraoperative cost did not differ between approaches (PL-LIF $17,206 vs LD-LIF $16,404, p = 0.462), nor did staff cost (p = 0.607), and exploratory value metrics did not establish a cost-effectiveness difference, whereas the impact score localized the between-approach difference to supply composition. Biologic impact varied most, with a more than two-fold range among the three surgeons (median approximately 5% to 19%) and higher biologic impact in LD-LIF within individual surgeons.

CONCLUSIONS: The impact score describes how intraoperative supply costs are distributed across categories. In this single-center, three-surgeon cohort, it identified a potentially modifiable cost driver that neither total cost nor exploratory value metrics revealed. Its use for cross-institutional benchmarking will require a multicenter study of how impact scores vary between institutions with differing vendor pricing and contracting. Because it reflects only the intraoperative phase, it complements, rather than replaces, episode-of-care and outcome-based value assessment.

STUDY DESIGN/SETTING: Retrospective single-center cohort study at a tertiary center.

LEVEL OF EVIDENCE: Level III, retrospective comparative study.