35. How many screws are necessary to be considered an experienced surgeon for freehand placement of thoracolumbar pedicle screws? Analysis of the learning curve using the cumulative summation test for learning curve (LC-CUSUM)

Abstract

BACKGROUND CONTEXT Several studies have demonstrated the learning curve for freehand pedicle screw placement (PSP) in residents, spinal fellows, and young surgeons. Also, the authors have suggested the numbers of required screws for PSP. Despite advances in statistical analysis for the learning curve, there is no study investigating how many screws are required to reach an adequate performance level in freehand PSP. PURPOSE The purpose of this study was to determine the amount of screws needed to achieve an adequate skill level for PSP via the freehand technique in the nondeformed thoracolumbar spine using the cumulative summation for learning curve (LC-CUSUM) analysis. STUDY DESIGN/SETTING A retrospective case series. PATIENT SAMPLE The first 85 patients who underwent thoracolumbar PSP using the freehand technique with postoperative computed tomography (CT) were included in the analysis. OUTCOME MEASURES The accuracy of PSP was evaluated using postoperative CT by an independent observer who was unaware of the purpose of this study. The accuracy of pedicle screw position was determined using a 5-grade system: Grade A, the screw was completely within the pedicle; Grade B, the screw breaches the pedicle's cortex by less than 2 mm; Grade C, pedicle cortical breach was less than 4 mm; Grade D, pedicle cortical breach was less than 6 mm; and Grade E, pedicle cortical breach of 6 mm or more. METHODS The surgeon had one year's experience of fellowship training in the tertiary teaching hospital. The learning curve of freehand PSP was investigated using LC-CUSUM analysis. Procedure success was defined as an acceptable accuracy of pedicle screw, which is divided into two groups (group 1: the screw breaches the pedicle's cortex by less than 2 mm, group 2: the screw is completely within the pedicle). RESULTS Total 52 cases and 313 pedicle screws were included and analyzed in this study. In group 1 accuracy, the LC-CUSUM signaled competency for freehand PSP at the 115th pedicle screw (17th case). In group 2 accuracy, the LC-CUSUM signaled competency for freehand PSP at the 312th pedicle screw (52nd case). This means that a trainee with no experience with freehand PSP reached adequate accuracy level of pedicle screw with less than 2 mm pedicle breaches at 115th screw, and with completely within the pedicle at 312th screw. The rate of pedicle screw breached the pedicle less than 2 mm (group 1) was 88.5% and the rate of accuracy of pedicle screw completely within the pedicle (group 2) was 70%. There were no major complications, such as neurovascular injury, and life-threatening complications. CONCLUSIONS In this study, the learning curve analysis demonstrated that a substantial learning period may be necessary before an adequate level of performance is achieved for freehand PSP in the non-deformed thoracolumbar spine. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.