How Patient-Specific Guides Can Ease the Learning Curve of Cortical Bone Trajectory: A Retrospective Study

The objective of the study was to compare operative time, estimated blood loss (EBL), length of stay (LOS), and perioperative complications between lumbar fusions performed with cortical bone trajectory (CBT) screw fixation using patient-specific instrumentation (PSI) versus freehand. Secondary objectives were to quantify the learning curve and economic impact of PSI.  Methodology: We reviewed all CBT lumbar fusions performed by a single surgeon between 2018 and 2025, comparing a freehand approach with CT-guided PSI assistance. Thin-cut CT scans were used to build individualized, 3D-printed guides. Propensity matching for age, sex, and levels fused produced balanced cohorts.  Results: In total, 247 CBT fusions were analyzed: 28 (11.3%) freehand and 219 (88.7%) PSI. After the introduction of PSI, annual CBT volume increased from roughly 7 to 55 cases. Matched comparisons showed that PSI reduced mean operative time by about 33 minutes (149.5 vs. 182.5 minutes, P = 0.003) and lowered EBL by roughly 75 mL (P = 0.026). Reoperation (4 vs. 10) and wound complication (0 vs. 3) rates were lower but not statistically significant. Among two-stage procedures, infection and reoperation rates dropped from 35.7% to 7.5% (P < 0.001). Overall efficiency per fused level improved by 18%-25 % (P = 0.02).

Use of PSI in CBT lumbar fusion shortened operations, reduced blood loss, and maintained safety, while allowing the surgeon to perform more cases with greater consistency. The results suggest PSI smooths the CBT learning curve and may offer practical cost savings through improved operating-room efficiency.