Thoracic Pedicle Screw Placement Using the Outside-In Technique: An Analysis Of Screw Placement Using Anatomic Landmarks Without Image Guidance

PURPOSE: To evaluate the safety of the “outside-in” technique utilizing only standard anatomic landmarks without image guidance.

MATERIALS & METHODS: 80 pedicle screws were placed from T4-T11 in 5 fresh cadaveric specimens. No imaging was utilized. All screws were placed using anatomic landmarks. Pedicles were dissected to determine breakout, and location of anatomic structures. Breakout was described as Grade 1 <1mm ,Grade II <2m, Grade III 2-4mm of screw penetration

RESULTS: 3 screws (3.75%) perforated the medial cortex: 2 Grade I, 1 Grade II. 4 screws (5%) violated the pedicle directly lateral: 2 Grade I, 1 Grade II, 1 Grade III. The rib laterally covered all screws. There were no pedicle violations superior or inferior.

CONCLUSIONS: The “outside-in” technique for thoracic pedicle screw placement is safe and utilizes the same anatomic landmarks at all levels. Our results are comparable to other published studies where image guidance was utilized.