SAP Principle Guided Free Hand Technique: A Secret for T1 to S1 Pedicle Screw Placement

Existing freehand techniques of screw placement mainly emphasized on various entry points and complex trajectory reference. The aim of this study is to illustrate a standardized and reliable freehand technique of pedicle screw insertion for open pedicle screw fixation with a universal entry point and a stereoscopic trajectory reference system and report the results from a single surgeon's clinical experience with the technique.

In this study, the author respectively reviewed a total of 200 consecutive patients who had undergone open freehand pedicle screw fixation with Superior Articular Process (SAP) technique from January 2019 to May 2020. For accuracy and safety, all 200 cases had undergone postoperative X-ray while 33 cases including spinal deformity, infection, and tumor had received additional CT-scan. Screw accuracy was analyzed via a CT-based classification system with Student's t test.

A total of 1126 screws had been placed from T1-S1 with SAP-guided freehand technique and the majority had been confirmed safe in X-ray without the need of CT scan. A total of 316 screws in deformity or infectious or tumor cases had undergone additional CT scan with 95.5% (189 of 198 screws) accuracy in thoracic group and 94.9% (112 of 118 screws) in lumbar group. The accuracy had been 90.5% (114 of 126 screws) in deformity group and 95.8% (182 of 190 screws) in non-deformity group. All perforation cases had been rated Grade B (<2 mm) without significant difference between the medial and the lateral (p < 0.05). No cases had been detected with significant neurological deficiencies. The mean intraoperative X-ray shots were 0.73 per screw.

SAP-guidance is a reliable freehand technique for thoracic and lumbar pedicle screw instrument. It allows accurate and safe screw insertion in both non-deformity and deformity cases with less radiation exposure.