The learning curve of pedicle screw placement: how many screws are enough?

STUDY DESIGN: A retrospective study. OBJECTIVE: Assess the learning curve of pedicle screw (PS) placement of a Spinal Surgery Fellow (SSF) with no previous experience with the technique. SUMMARY OF BACKGROUND DATA: Recent studies have attempted to identify the learning curve for different surgical procedures to define training requirements. Several authors have described a learning curve for PS placement. However, no one has defined the number of PS necessary to be competent in this skill. METHODS: All patients who had PS inserted by the SSF under the supervision of an Attending Spinal Consultant (ASC) and had adequate postoperative radiographs and computed tomography scans available, were included in this study. PS position was assessed by 2 blinded independent observers using a grading scale. PS placement by the SSF was evaluated by examining the assessed position in chronological groups of 40 screws. RESULTS.: Ninety-four patients underwent internal fixation of the spine with 582 PS. Eight cases (40 screws) were excluded because of lack of imaging studies. Of the 542 screws under evaluation, 320 (59%) were performed by the SSF, 187 (34.5%) by the ASC, and 35 (6.5%) by advanced orthopedic or neurosurgical trainees.The rate of misplaced PS performed by the SSF for the first 80 PS was 12.5% and dropped to 3.4% for the remaining 240 screws, which is a statistically significant difference (P < 0.01). Evaluation of computed tomography of vertebrae with PS placed by the SSF on one side and by the ASC on the other showed that the ASC achieved better placement during the first 80 PS (P < 0.01). However, this difference disappeared in the last 240 (P = 1.00). CONCLUSION: The findings demonstrate a learning curve for PS placement. In this series, the asymptote for this technique for an inexperienced SSF, started after about 80 screws (approximately 25 cases).