V sign reliable landmark for identifying S1 pedicle entry point under fluoroscopic guidance

Sacral (S1) pedicle screw misplacement in posterior percutaneous fixation (PPF) can be related to anatomical variability and a lack of reliable radiographic landmarks. It might lead to iatrogenic injuries to adjacent neurovascular structures and sometimes to the need for revision surgery.

Tony Tannoury et al conducted a study to highlight a reproducible anatomical landmark (the “V” sign) for the safe localization of the S1 pedicle entry point under fluoroscopy. Investigation performed at Boston Medical Center, Boston, Massachusetts. The study has been published in “JBJS Open Access.”

Human cadavers (n = 14) were dissected for the anatomical description of the “V” landmark and its relationship with the entry point of the S1 pedicle screw. The “V” landmark was defined medially by the lateral border of the superior articulating process of S1 and laterally by the posterior projection of the sacral ala. The mean distance was measured between the bottom point of the “V” landmark and the anatomical entry point to the S1 pedicle (V-S1 entry point distance). A similar measurement was conducted on computed tomography (CT) scans of 135 patients who underwent PPF using the “V” sign as a landmark for S1 pedicle screw placement (270 screws). These were retrospectively evaluated for appropriateness of S1 screw entry points and for proper S1 screw alignment and breaches.