Which Modality Best Predicts Pedicle Screw Purchase for Lumbar Degenerative Disorders - DEXA or QCT or MRI?

Abstract Study design: Prospective Observational study Objective To find out which modality best predicts the pedicle screw purchase on bone, measured by intra operative screw insertional torque. Additionally, we obtained biopsy from the vertebral body during surgery and correlated the scores provided by DEXA, QCT and MRI. Methods All patients undergoing lumbar decompression and fixation surgery for degenerative disorders with age more than 50 years were included. Preoperative BMD assessment was done by DEXA, QCT and MRI within 72 hours prior to surgery. During surgery bone biopsy sample were collected before putting the pedicle screw and was sent for histomorphometric assessment and insertional torque of pedicle screw measured with torque measuring device while inserting the screw. These intraoperative parameters were correlated with the preoperative measurements of DEXA, QCT and MRI by using appropriate Pearson’s coefficient. Results A total of 53 patients were included in the study. The mean DEXA BMD was 1.18 ± 0.23 g/cm², mean DEXA T score was (-)0.13 ± 1.87. The mean QCT BMD value was 123.91 ± 44.83 mg/cm³, mean QCT T score was (-)1.54 ± 1.79. The mean MRI VBQ (vertebral bone quality) score was 2.71 ± 0.69. The DEXA, QCT and MRI scores were correlated with screw insertional torque. The correlation scores were 0.27and 0.186 for QCT BMD and T scores and 0.393 and 0.437 for DEXA BMD and T scores and it was (-)0.113 for MRI VBQ – showing that DEXA had better correlation with Torque than the rest. Similar correlation was done with bone biopsy scores, the correlation scores were (-)0.285 and (-)0.261 for QCT, (-)0.121 and (-)0.203 for DEXA and 0.224 for MRI scores. QCT had better correlation with Biopsy like that with MRI. Conclusion Our study is unique in comparing 3 preoperative investigations prior to surgery and attempting to correlate their efficacy in the diagnosis of Osteoporosis in the surgical context of a good pedicle screw purchase. We found that the correlation between DEXA and Pedicle Screw Insertional Torque to be higher than that of either QCT and MRI. QCT has better correlation with Biopsy similar to that with MRI.