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 (stdß=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.

High bone turnover elevates the risk of denosumab-induced hypocalcemia in women with postmenopausal osteoporosis.

Hypocalcemia is the most common major adverse event in patients with osteoporosis receiving the bone resorption inhibitor denosumab; however, limited information is available regarding risk factors of hypocalcemia. Therefore, this study aimed to identify the risk factors of hypocalcemia induced by denosumab treatment for osteoporosis. We retrospectively reviewed the records of patients who had received initial denosumab supplemented with activated vitamin D for osteoporosis. Serum levels of the following bone turnover markers (BTMs) were measured at baseline: bone-specific alkaline phosphatase (BAP), total N-terminal propeptide of type 1 procollagen (P1NP), tartrate-resistant acid phosphatase 5b (TRACP-5b), and urinary cross-linked N-telopeptide of type 1 collagen (NTX). Of the 85 denosumab-treated patients with osteoporosis studied, 22 (25.9%) developed hypocalcemia. Baseline serum total P1NP, TRACP-5b, and urinary NTX were significantly higher in patients with hypocalcemia than in those with normocalcemia following denosumab administration (all P<0.01). Multivariate logistic regression analysis revealed that patients with total P1NP >76.5 µg/L, TRACP-5b >474 mU/dL, or urinary NTX >49.5 nmol bone collagen equivalent/mmol creatinine had a higher risk of hypocalcemia (P<0.01). Our study suggests that denosumab may have a greater impact on serum calcium levels in patients with postmenopausal osteoporosis with higher baseline bone turnover than in patients with postmenopausal osteoporosis with normal baseline bone turnover, because maintenance of normal serum calcium in this subgroup is more dependent on bone resorption. Close monitoring of serum calcium levels is strongly recommended for denosumab-treated patients with high bone turnover, despite supplementation with activated vitamin D and oral calcium.