1. INTRODUCTION A major limitation of C-arm fluoroscopy is the inability to capture radiographic images in more than one anatomical plane at a time. The G-arm (Whale Imaging, Waltham, MA, Figure 2) is a novel imaging device with the capability of obtaining simultaneous AP and lateral images. This ability allows an intuitive representation of anatomic structures to the surgeon and eliminates the need to adjust the fluoroscope configuration for multi-plane images. MATERIALS AND METHODS A fellowship trained spine surgeon without previous experience using G-arm fluoroscopy performed 32 consecutive percutaneous pedicle screw insertions on 2 cadavers from T10 to L5 (8 total screws with C-arm, 24 total screws with G-arm) utilizing a randomized insertion protocol. Screw placement accuracy was assessed postoperatively utilizing high-resolution spiral CT imaging (Figure 1). An ideally placed pedicle screw received 10 points Total implantation time was recorded by an independent observer for each chronologically inserted screw RESULTS The total procedure time stabilized at approximately 6 minutes after the fourth chronologic C-arm guided procedure Procedure time stabilized at approximately 4 minutes without loss of screw accuracy when G-arm guidance was used C-arm guided screws were inserted with an average accuracy score of 8.5/10 for chronologic screw #1-4 and 7.5/10 for chronologic screw # 5-8 G-arm guided chronologic screws 1-5 had a mean accuracy score of 7.8/10 and a mean insertion time of 6.4 minutes. Chronologic screws 20 through 24 had a mean accuracy score of 9.4/10 and a mean insertion time of 3.5 minutes, which were both significantly better than the C-arm group (p<0.05). CONCLUSIONS This study demonstrates that overall accuracy and procedure time were significantly improved with simultaneous bi-plane image guidance Accuracy is adversely affected as pedicle screws are inserted more rapidly with use of C-arm image guidance whereas accuracy is not affected by more rapid insertion of screws under G-arm guidance The learning curve of the G-arm imaging technology was overcome after approximately 10 consecutive procedures Future investigation is underway to determine radiation dose delivery to the patient and OR staff. We hypothesize that the G- arm will lower overall radiation exposure since the need for multiple test shots when changing imaging plane configuration is eliminated Assessment of the Initial Learning Curve Experienced with Portable, Multi-Plane Image Guided Percutaneous Pedicle Screw Insertion Joseph A. Sclafani MD 1, Kevin Liang PhD 1, Yu-Po Lee MD 2 1 Milestone Research Organization, San Diego, CA 2 University of California, San Diego, CA, USA Figure 4. The screw accuracy score suffered with faster insertion times when the C-arm was used. In contrast, screw accuracy did not suffer with faster insertion times with G-arm image guidance. Figure 2. G-arm multi-plane imaging technology displays simultaneous AP and lateral intraoperative views Figure 1. Parameters of screw accuracy scoring system. Axial computed tomography scan showing parameters of length, medial and lateral containment, and trajectory (A). Sagittal computed tomography scan showing sagittal containment and sagittal trajectory parameters (B). The clinically relevant parameters (medial and lateral containment, axial trajectory) are weighted for greater impact on the scoring scheme. Figure 3. Mean accuracy score from the initial and final series of screws inserted with each imaging technology. Points awarded 210 Length ¾ through vertebral body ± 5% ¾ through vertebral body > 5% Axial trajectory Parallel to pedicle axis ± 5˚ 5-10˚ angle to pedicle axis >10˚ angle to pedicle axis Sagittal trajectory Parallel to endplate ± 5˚ 5-10˚ angle to endplate >10˚ angle to endplate Medial/Sag containment Complete containment Breached screw thread Breached screw body Lateral containment Complete containment Breached screw thread G-ArmC-Arm Screw 1-5 Screw 20-24 Screw 1-4Screw 5-8 C-arm insertion time vs. chronologic screw # G-arm insertion time vs. chronologic screw # C-arm accuracy vs. chronologic screw #G-arm accuracy vs. chronologic screw #