Neuromuscular scoliosis with severe pelvic obliquity: the accuracy of S 2AI screw placement by O-arm three-dimensional CT navigation / 中华骨科杂志

ABSTRACT

Objectives:To investigate the feasibility of second sacral alar-iliac (S 2AI) screw placement and trajectories index in patients with neuromuscular scoliosis with severe pelvic obliquity; and to explore the accuracy of S 2AI screw placement by O-arm three-dimensional (3D) CT navigation (Medtronic, Minneapolis, MN, USA). Methods:All of 28 patients with neuromuscular scoliosis who underwent posterior long fusion with S 2AI between January 2017 and August 2020 were reviewed, with an average age of 22.2 years old (ranged from 10 to 51 years), and the pelvic obliquity angle was 27.54±9.90° (ranged from 16.2° to 53.6°). Based on 3D CT reconstruction of these specimens, virtual S 2AI screw channels were identified and measured. Entry point was determined by 1 mm inferior and 1 mm lateral to the S 1 dorsal foramen, and virtual S 2AI screw trajectories with maximum length and width were explored by rotating 3D pelvis. The parameters of the determined channels were measured including caudal angulation on the sagittal plane (sagittal angle, SA), lateral angulation on the transverse plane (transverse angle, TA) and the maximal length of the channel (maximal length, ML). The accuracy of screw placement was evaluated by postoperative pelvic CT scan. Results:All of the virtual S 2AI screw trajectories can be reconstructed. The screw trajectory parameters were shown as follows SA was 30.20°±21.94° and 50.94°±16.02° on the high and low sides of pelvis, respectively, and the difference was statistically significant ( t=3.990 , P<0.001). SA was 30.14°±21.93° on the anterior side of the pelvis and 51.00°±15.96° on the posterior side, respectively, with statistical significance ( t=4.027, P<0.001). TA was 43.67°±12.86° on the high side of pelvic tilt and 31.95°±13.80° on the low side, with statistical significance ( t=2.834, P=0.009). TA was 42.56°±12.52° on the anterior side of the pelvis and 33.05°±14.94° on the posterior side, respectively, and the differences were statistically significant ( t=2.192, P=0.037). ML was 97.12±12.44 mm and 92.28±11.04 mm on the high and low side of pelvis, and there was no significant difference ( t=0.963 , P=0.060). ML was 97.72±12.41 mm on the anterior sides of the pelvis and 91.68±10.57 mm on the posterior side, and the difference was statistically significant ( t=2.556 , P=0.017). SA tended to be smaller on the high side of pelvic tilt ( r=0.474, P<0.01) and TA tended to be higher on the anterior side of pelvis ( r=-0.419, P<0.01) . Only 2 screws (3.6%) showed screw breaches after surgery, with no clinically notable neurovascular or visceral complications. Conclusion:In patients of neuromuscular scoliosis with severe pelvic obliquity, the virtual S 2AI screw trajectory can be found in 3D CT reconstruction of the pelvis. But the parameters are very discrete at SA and TA. In these patients, the O-arm 3D CT navigation can be used to make sure the direction and length of the S 2AI screw, greatly improving the accuracy of screw placement and effectively descending the ratio of poor screw.