Is the Sacral Pedicle Screw Adequate as the Distal Anchor in Multi-level Fixation of the Lumbosacral Spine with Lateral Lumbar Interbody Fusion?

<p>Introduction: We have employed the sacral pedicle screw (S1PS) as the distal anchor in multi-level fixation of the lumbosacral spine combined with lateral lumbar interbody fusion (LLIF). However, S1PS loosening has been frequent. The present study aims to investigate the loosening of S1PS, cage subsidence, and fusion rate in multi-level lumbosacral fixation combined with LLIF.</p><p>Methods: We evaluated fourteen patients diagnosed with lumbar canal stenosis and degenerative scoliosis who underwent multi-level lumbosacral fixation with LLIF. CT images were used to evaluate radiological findings, including radiolucent zones around sacral screws, cage subsidence, loss of correction in lumbosacral lordosis, and bone fusion at L5/S postoperative 1 year.</p><p>Results: S1PS loosening was confirmed in 9 cases (9/14, 64%) at 3 months postoperatively, and in 13 cases (13/14, 92%) at 6 months postoperatively. The mean correction loss of lordosis at L5/S was 4.3° at 1 year postoperatively, and cage subsidence was observed in 10 cases (10/14, 71%). Bone fusion at L5/S was achieved in only 7 cases (7/14, 50%) at 1 year postoperatively. In the cases with no loosening of S1PS, the mean sacral Hounsfield unit was relatively high (215.3, Mean: 149.4), and both S1PS were inserted using a bicortical trajectory. In cases where both S1PS were inserted using a monocortical trajectory, a successful fusion of L5/S was only achieved in one out of six cases (16.6%).</p><p>Conclusions: S1PS loosening occurred in 91% of the patients. Patients with multi-level lumbosacral fixation combined with LLIF have a high risk of S1PS loosening when used as the most distal anchor.</p>