Femoral Bone Mineral Density Shows Stronger Correlation With Pedicle Screw Insertional Torque than Lumbar Bone Mineral Density or Hounsfield Units: A Retrospective in Vivo Study

Objectives Instrumentation failure remains a significant complication in spinal surgery. Preoperative bone health assessment is critical prior to spinal fusion surgery. Currently, bone mineral density (BMD) and Hounsfield Unit (HU) are common preoperative assessments, although it remains unclear which is more predictive of screw fixation strength. We aimed to identify the most reliable preoperative evaluation method for predicting screw insertional torque in patients undergoing lumbar fusion surgery. Methods Patients who underwent lumbar fusion surgery utilizing pedicle screws between 2021 and 2023, were prospectively registered in our database. All participants underwent preoperative lumbar CT and Dual-Energy X-ray Absorptiometry (DEXA) scans. We analyzed data from 109 patients who underwent lumbar fusion surgery with 6.5 mm pedicle screws. Preoperative BMD was measured via DEXA (lumbar spine and femur), and HU values were obtained from preoperative lumbar CT scans. Insertional torque of the screws was measured intraoperatively using a calibrated torque wrench. Correlations between insertional torque and BMD/HU as well as patients’ demographic/lab data were analyzed. Results A total of 335 pedicle screws were analyzed. Femoral BMD exhibited the strongest correlation with insertional torque (r = 0.557, P < 0.001), compared with lumbar BMD and HU. Age, ASA grade, BMI, serum calcium, and albumin showed weak correlations. Conclusions Femoral BMD demonstrated the strongest, although still moderate, association with intraoperative insertional torque among all preoperative bone quality measures evaluated, suggesting that it may offer a more informative estimate of underlying bone strength in patients undergoing lumbar fusion.