A Novel Method for the Prediction of the Pedicle Screw Stability: Regional Bone Mineral Density Around the Screw.

STUDY DESIGN: Prospective feasibility study on consecutive patients.

OBJECTIVE: The aim of this study was to investigate the ability of regional BMD around the pedicle screw to predict the screw fixation.

SUMMARY OF BACKGROUND DATA: Pedicle screw fixation is the gold standard technique for spinal fusion. Despite the advantage of biomechanical stability, screw loosening is a common complication. In previous studies, pullout strength and screw insertional torque were correlated, and most importantly, affected by bone mineral density (BMD). Although the density and structure of the vertebral body are not homogeneous, no study has yet evaluated the relationship between screw insertional torque and regional BMD around the pedicle screw in vivo.

METHODS: Consecutive 50 patients, scheduled for transpedicular fixation, were evaluated preoperatively for BMD measured by dual-energy absorptiometry (DXA) and quantitative computed tomography (QCT). Regional volumetric BMD around the pedicle screw (PS-vBMD) using the novel QCT technique was also evaluated. Among all patients, 190 screws (diameter, 7.5 to 8.5 mm; length, 40 to 45 mm, inserted from L1 to L5) were eligible for this study and were analyzed to identify factors contributing to insertional torque. The following factors were investigated: age, body mass index, laboratory data, pedicle diameter, screw diameter, screw length, and 5 types of bone mineral density measures [DXA: spine-areal BMD (aBMD), total hip-aBMD, femoral neck-aBMD, QCT: central-vBMD, PS-vBMD].

RESULTS: Insertional torque was significantly correlated with each BMD measurement and strongest with PS-vBMD (r=0.61, P<0.001). Multiple regression analysis showed PS-vBMD was most strongly correlated with screw insertional torque (stdβ=0.494; P<0.001). A model containing the following 5 predictors was significantly associated with screw insertional torque: age, pedicle diameter, screw diameter, screw length, and PS-vBMD.

CONCLUSIONS: The preoperative measurement of PS-vBMD was technically feasible and reliably predictive of screw insertional torque during transpedicular fixation in a clinical setting.