Segmental lordosis and bone fusion rate at L5/S1 after lumbosacral intervertebral fusion

<p>Purpose: We investigated the bone fusion rate, segmental lordosis, and risk factors for bone union failure at L5/S1 in multi-level lumbosacral interbody fusion.</p><p>Methods: This retrospective study included 35 patients who underwent lumbosacral interbody fusion at our hospital and were followed up for more than 2 years after surgery.Bone fusion rate according to number of interbody fusion, the cage material, and the number of cages, and segmental lordosis (SL) at L5/S1 for each cage lordotic angle were examined. Various parameters were compared between the group with bone fusion group at L5/S1 (U group) and the group without non-union at L5/S1 (N group).</p><p>Results: The bone fusion rate at L5/S1 was 87% for 2 intervertebral fusion, 73% for 3 intervertebral fusion, and 62% for 4 intervertebral fusion. The bone union rate was the lowest in 4 intervertebral fusions. Preoperative PI, postoperative PI-LL, and postoperative SVA were significantly larger in the N group. Multivariate analysis detected preoperative PI as the risk factor of fusion failure at L5/S1, with a cutoff value of 51° and an area under the curve of 0.807. Mean SL improved from 5° preoperatively to 10° postoperatively. SL increased according to the lordotic angle of the cage, and the correlation coefficient was 0.73 (p<0.001), indicating a significant correlation.</p><p>Conclusion: The results show that the higher the number of interbody fusion, the lower the rate of bone union. PI was a risk factor for bone fusion failure, with a cut-off value of 51°. Postoperateve SL was correlated with cage lordosis angle, but bone union rate was not correlated with cage material and cage number.</p>