174. Cage position effect on subsidence and segment lordosis angle after OLIF operation: a new scoring system for treatment decision

Abstract

<h3>BACKGROUND CONTEXT</h3> Oblique lateral interbody fusion (OLIF), a minimally invasive operation has shown advantages in small trauma, quick recovery and indirect decompression, was commonly used in lumbar degenerative disease and scoliosis. Cage position affects SLA and cage subsidence. The risk factors affecting cage placement were unknown as was which patients could be candidates for OLIF. <h3>PURPOSE</h3> To study the relationship between cage position and segmental lordosis angle (SLA), cage subsidence after OLIF, and to develop a new scoring system for treatment decision according to risk factors affecting cage position. <h3>STUDY DESIGN/SETTING</h3> Retrospective study to study the relationship between cage position and SLA, OLIF, and to develop a new scoring system for treatment decision according to risk factors affecting cage position. <h3>PATIENT SAMPLE</h3> OLIF patients with average of 22 ± 10.7 months follow-up and continuous collection—141 L4-5 OLIF patients. <h3>OUTCOME MEASURES</h3> SLA, intervertebral height index (IHI) and foraminal height (FH), cage subsidence, the shape and position of the iliac crest, endplate morphology and anterior position of psoas. <h3>Methods</h3> A total of 72 patients with 93 segments with average of 22 ± 10.7 months follow-up were enrolled in this study. The SLA, IHI and FH were collected at preoperation, 3 days after operation and the last follow-up. The patients were divided into two groups, group 1 (50% ahead, 55 segments) and group 2 (50% back, 38 segments) according to whether the center point of cage exceeded the middle line of the lower endplate and investigate the relationship between the cage's position, and the recovery and maintenance of SLA, and find risk factors affecting cage position. <h3>Results</h3> The subsidence rate, SLA loss in follow-up in group 1 was significantly lower than group 2, (1.8% vs 28.9%), 0.9 ± 1.2° vs 3.5 ± 2.3°, and the increased of SLA 5.9 ± 3.9° vs 4.2 ± 3.1° was higher in group 1(p<0.05). Logistic regression analysis showed cage subsidence and cage position at the back 50% is the main risk factor for SL loss more than 3° (OR:17.7, 8.0). Further study showed that the shape and position of the iliac crest, endplate morphology and anterior position of psoas was the main factor affecting cage placement in L4-5. Then a new scoring system was designed and the continuously collected 141 L4-5 OLIF patients showed there was significant correlation between cage position and score (r=0.58, p<0.01). Score more than 6 points is the main risk factor for cage placed at the back 50% (OR:5.9). <h3>Conclusions</h3> The cage position affects cage subsidence and the SLA after OLIF operation. And according to the new scoring system, we suggest that the surgical plan should be carefully designed for patients with more than 6 points. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.