Measurement of Intraoperative Insertional Torque: Usefulness for Prediction of the Deviation of Pedicle Screw Insertion in Lumbar Degenerative Diseases.

Background: Measurement of screw insertional torque (SIT) can be valuable to predict rigid pedicle screw (PS) fixation without instrumentation failure. Numerous biomechanical studies support this concept; however, the value of measuring intraoperative SIT has not been well investigated. The aim of this study was to identify the relationship between the SIT values in PS fixation surgery and clinical factors in lumbar degenerative surgery.

Methods: We conducted a retrospective analysis of 492 PSs in 114 patients who underwent lumbar fusion surgery between July 2014 and April 2022. Intraoperative SIT values were measured using an analog torque wrench. Patient characteristics, radiological factors, and the accuracy of PS insertion were analyzed to assess their associations with the strength of the SIT.

Results: Intraoperative SIT showed significant correlations with age (r = -0.196, P < 0.001), bone mineral density (r = 0.399, P < 0.001), and body mass index (r = 0.165, P < 0.001). The torque ratio, reflecting bilateral SIT difference within the same vertebra, was significantly higher in cases with unilateral PS deviation >2 mm compared with ≤2 mm.

Conclusions: The findings suggest that patient-related factors play a role in screw fixation strength, and the torque ratio may serve as a useful indicator for assessing PS placement accuracy.

Clinical relevance: Intraoperative screw insertional torque measurement correlates with bone mineral density, age, and body mass index and may help predict fixation rigidity and prevent instrumentation failure in lumbar fusion surgery.

Level of evidence: 3: