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.
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.