Early and long-term changes in adjacent vertebral body bone mineral density determined by quantitative computed tomography after posterolateral fusion with transpedicular screw fixation

The aim of this study is to investigate vertebral body bone mineral density (BMD) changes following posterolateral fusion with transpedicular screw fixation using quantitative computerized tomography (QCT) in short and relatively long-term periods.A retrospective study was performed to investigate vertebral body BMD changes in the patients who underwent posterolateral fusion with transpedicular screw fixation at thoracic and lumbar spine. A total of 160 patients were enrolled into the study. According to the follow-up period, patients were divided into two subgroups (group 1, early follow-up, mean follow-up period, 279.3±162.3 days and group 2, later follow-up, mean follow-up period, 969.1±274.2 days). The trabecular BMDs (mg/cm³) were measured from T12 to L5 as screw free levels by using QCT measurement software. Comparisons between preoperative and postoperative BMD values were assessed using paired t-test.The mean postoperative BMD values of both group 1 and 2 weresignificantly lower, compared with the preoperative values (79.2±31.3mg/cm³ vs. 91.5±31.4mg/cm(3), 76.1±25.5mg/cm(3) vs. 89.3±30.4mg/cm(3), p<0.001 and p<0.001, respectively). There was no significant correlation between BMD loss and number of fused segments. Vertebral BMD loss was significantly higher in the L3 vertebra when located caudally to the operation site than when located cranially (-27.7±19.8% vs. -12.8±27.1%; p<0.01).The vertebral body BMD values are decreased at the adjacent of the posterolateral fusion with transpedicular screw fixation levels in both cephalad and caudad sides at an average of 9-months-follow-up postoperatively. This BMD loss persisted, but not worsened at an average of 32-months-follow-up. Vertebral BMD loss was significantly higher in the L3 vertebra when located caudally versus cranially to the surgery site.