Assessment of maximal insertional torque of cervical and thoracic screws during posterior spinal surgery.

STUDY DESIGN Multicenter intraoperative biomechanical analysis. PURPOSE This study aimed to assess the maximal insertional torque (MIT) of lateral mass screw (LMS) and pedicle screw (PS) in the cervical or thoracic vertebrae during surgery. METHODS During posterior spinal fusion, cervical or thoracic multi-axial screws were placed at different cervical or thoracic levels and the MIT was recorded for each screw revolution using an analogue torque wrench. Screw number was as follows: 11 PS at C7, 134 LMS (C3-6) (Magerl technique, 70; Roy-Camille technique, 64), and 33 PS in the thoracic region. RESULTS Average MIT values (cNm) were as follows: for PS (diameter: 3.5 mm) at C7, 45.3 ± 21.9 in men and 60.0 ± 20.1 in women (p=0.28); for Magerl screws, 69.0 ± 20.5 in men and 58.6 ± 15.7 in women (p=0.13); and for Roy-Camille screws, 51.0 ± 17.9 in men and 42.4 ± 15.9 in women (p=0.52). The average MIT for Magerl screws was significantly higher than that for Roy-Camille screws in men and women (both p<0.01). CONCLUSIONS Intraoperative insertional torque could be a good indicator to evaluate the purchase and help guide decisions on screw type and insertion technique. Further postoperative assessments with sequential X-rays are needed to reveal the significance of MIT during posterior spinal fusion.