Advantage of Pedicle Screw Placement Into the Sacral Promontory (Tricortical Purchase) on Lumbosacral Fixation

Abstract

Retrospective clinical study. To evaluate the clinical outcome of the tricortical method for lumbosacral fixation. Despite advances in surgical techniques, failure to achieve solid arthrodesis of the lumbosacral junction continues to be significant clinical problems. To overcome these problems, tricortical purchase fixation has recently been advocated and studied. In this method, a trajectory directly into the medial sacral promontory is used to gain purchase in the dorsal, anterior, and superior cortices. This fixation method has been shown to double the insertional torque of the classic bicortical technique. Patients who had undergone lumbosacral fixation were included in this study. The average area of fusion was 1.7 segments. The patients were divided into a tricortical fixation group (TF, n=98) and a nontricortical fixation group (non-TF, n=33). We examined clinical outcome [Japanese Orthopaedic Association scoring system (JOA score)], fusion status, and the characteristics and safety of pedicle screwing in both groups. To identify risk factors for postoperative loss of lordosis (postoperative loss of >5 degrees in L5/S1 disk angle), risk factor analysis was performed by multivariate logistic regression. In TF and non-TF, the JOA score changed from 13.4 and 13.8 points at surgery to 24.9 and 23.8 points, respectively, at final follow-up, and the recovery rate was 73.7% and 64.2%, respectively. Pseudoarthrosis of the fused L5/S1 occurred in 3 patients in whom the lumbosacral spine had not been fixed by tricortical purchase. The screw angle was 22.0 and 16.1 degrees in TF and non-TF, respectively, that is, a significant difference was shown. Significantly fewer TF cases encountered the risk of injured vascular tissue compared with non-TF. Non-TF (OR, 3.37) and correction of the L5/S1 disk angle (OR, 1.11) were significant risk factors for postoperative loss of lordosis. In patients who underwent short-segment lumbosacral fusion, TF enhanced postoperative stability at the lumbosacral junction. Pseudoarthrosis did not occur in patients who underwent TF, and the risk of vascular injury was less. TF is regarded as a successful technique in short-segment lumbosacral fixation.