A Structured Ultrasound-Guided Workflow for Level Identification in Lumbar Spine Surgery

Study Design. Cadaveric validation study Objective. To evaluate the accuracy of a structured four-step ultrasound (US)–guided workflow for lumbar spinal level identification (SLI) using cadaveric specimens. Summary of Background Data. Despite the routine use of fluoroscopic verification, wrong-level spinal surgery continues to be a documented and concerning complication. Fluoroscopy exposes patients and staff to ionizing radiation and requires specialized personnel and infrastructure. US has been utilized for SLI in obstetric and anesthetic applications but remains underexplored in surgical workflows. Methods. Ten fresh-frozen cadavers underwent US imaging to identify lumbar levels. A newly developed four-step protocol was employed: (1) Midline localization, (2) Sacral surface tracing, (3) S1-Superior articular process (SAP) recognition, (4) Interlaminar space enumeration. Five spinal needles were placed under US guidance in each specimen (L1-2 through L5-S1), with one needle per level. Fluoroscopic imaging was then used to confirm needle placement accuracy. A level was defined as misidentified if the projected trajectory from the needle tip violated predefined radiographic boundaries. Results. A total of 50 lumbar levels were assessed across ten cadaveric specimens, with 25 procedures performed from the right side and 25 from the left. Fluoroscopic validation demonstrated accurate level identification in 49/50 cases, yielding an accuracy rate of 98%. The single misidentification occurred at the L5-S1 level during the third step of the workflow, where the S1 SAP was erroneously interpreted as the L5 inferior articular process. No systematic error patterns were observed, and the four-step protocol proved reproducible across specimens. Conclusion. This cadaveric feasibility study establishes a high accuracy of US-guided lumbar level identification. A structured and reproducible workflow for level localization was established, integrating a novel four-step protocol. These findings represent a first step toward a radiation-free alternative for preoperative lumbar level verification in spinal surgery. Further investigations are warranted to validate these results in clinical settings.