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Comparison Between Gearshift And Drill Techniques For Pedicle Screw Placement By Resident Surgeons

Jonathan Allen, MD,1 Yusuf T. Akpolat, MD,1 Shyam Kishan, MD,2 Tim Peppers, MD,3 Farbod Asgarzadie, MD,4 Wayne K. Cheng, MD1

1Department of Orthopaedic Surgery, Loma Linda University 2Department of Orthopaedic Surgery, Indiana University 3Department of Orthopaedic Surgery, Seaside Spine 4Department of Neurological Surgery, Loma Linda University



Various techniques have been described for pedicle screw placement with established clinical and radiological success. Suboptimal screw trajectories can compromise bony purchase and, worse yet, cause neurological and vascular injuries. Thus, it is of paramount importance to achieve maximum accuracy of screw placement. Our objective is to evaluate the accuracy of pedicle screw placement in the thoracolumbar spine by resident surgeons. Two popular techniques, gearshift versus drill, were compared.


This is a a cadaveric surgical technique comparison study. Six resident surgeons instrumented the spine from T1 to S1 using both gearshift and drill techniques. Each pedicle was randomly assigned to either of the techniques. Pedicle screws were placed freehand without radiographic guidance. Violations (medial, lateral, anterior, superior and inferior) were recorded by studying the computerized tomographic scans of instrumented cadavers by blinded observers. Critical perforations were defined as greater than 2mm breach of the pedicle wall.


A total of 100 vertebrae (200 pedicles) were instrumented in the six cadavers. 103 pedicles were breached (51.5% of total pedicles). Lateral violations were the most encountered (65% of violations, 67 total, 48 critical, 19 noncritical) followed by medial (24%, 25 total, 13 critical, 12 noncritical), and the rest were anterior (3%), superior (4%) and inferior (4%). There was no overall difference in violations comparing the gearshift technique (49.5%, 51 total, 37 critical, 14 noncritical) with drill technique (50.5%, 52 total, 33 critical, 19 noncritical). Analyzing the breaches at individual vertebra indicated most violations at T6 (11), T5 (10), followed by T3 (9) and T4 (9), decreasing towards the lumbosacral vertebrae.


The results of this study suggest that the gearshift and drill techniques for placement of pedicle screws in the thoracolumbar spine fare similarly with regards to risk of breach when applied by resident surgeons.

Pedicle screw instrumentation, resident surgeon, gearshift, drill, pedicle violation, cortical violation, critical violation, noncritical violation, vertebral segment, Accuracy, safety.
Volume 9 Article 23