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Cadaver study.To evaluate with direct observation the errors made when novice resident surgeons place thoracic pedicle screws. To determine how many specimens need to be instrumented to assure an improvement in accuracy to currently published levels.Thoracic pedicle screw instrumentation has been shown to provide numerous benefits in spinal deformity surgery including 3 column fixation of the spinal elements, decreased need for thoracoplasty or anterior thoracic release and decreased operative time and blood loss.Three orthopaedic residents inexperienced in pedicle screw placement received an introductory teaching session. Intact thoracic vertebral body specimens were harvested from 15 cadaver spines. Each vertebral body was mounted on a clear Plexiglas frame with only the posterior surface anatomy visible to the surgeon. Each resident surgeon instrumented 5 thoracic spines verbalizing all perceived pedicle wall violations as they occurred. An observer recorded the accuracy of the gearshift probe, flexible probe, tap, and screw placement. Critically perforated screws were defined as a greater than 2 mm breach of the pedicle wall.Two hundred ninety-seven pedicles in 149 intact vertebral body specimens were instrumented. Eighty-five (29%) screws were not fully within the pedicle. Sixty-three (74%) were noncritical violations and 22 (26%) were critical violations. There were 18 (21%) screw violations not perceived by the surgeon to be outside the pedicle. There was a decrease in the proportion of total screw violations by the third cadaver (P < 0.001) and in critical screw violations by the fourth cadaver (P = 0.01).Novice resident surgeons placing thoracic pedicle screws in cadavers were able to significantly improve by the fourth cadaver to accuracy levels documented in the literature. Surgeons in training shouldpractice these skills in the laboratory before proceeding to the operating room.