Does loss of spondylolisthesis reduction impact clinical and radiographic outcomes after minimally invasive transforaminal lumbar interbody fusion.

BACKGROUND CONTEXT Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is the workhorse minimally invasive treatment for patients with degenerative lumbar stenosis and spondylolisthesis refractory to nonoperative care. While the basic tenets of surgical treatment do not differ between minimally invasive and open techniques, surgeons performing MI-TLIF are more likely to attempt reduction of spondylolisthesis in order to optimize restoration of canal dimensions due to a greater reliance on indirect decompression, which has been shown to be effective. While intraoperative reduction is often successful, postoperative loss of reduction and slip recurrence can be seen. PURPOSE To determine the rate and clinical impact of slip recurrence after MI-TLIF with expandable cage technology. STUDY DESIGN/SETTING Retrospective cohort study. PATIENT SAMPLE Patients undergoing MI-TLIF for degenerative spondylolisthesis using an articulating, expandable cage OUTCOME MEASURES Patient-reported outcome measures (PROMs), including the Oswestry Disability Index (ODI), visual analog scale (VAS) for back/leg pain, Short Form-12 (SF-12) and PROMIS Physical Function (PF) METHODS Patients undergoing MI-TLIF for degenerative spondylolisthesis using articulating, expandable cages from 2017-2019 were retrospectively studied. Lateral radiographs were reviewed and evaluated for the presence or absence of spondylolisthesis preoperatively, intraoperatively, and at follow-up times including 2 weeks, 6 weeks, 12 weeks, 6 months and 1-year postoperatively. Spondylolisthesis was measured from the posterior inferior corner of the cephalad vertebra to the posterior superior corner of the caudal vertebral, with any measurement >1mm classified as spondylolisthesis, and Meyerding grade was noted. Intraoperative reduction was measured and loss of reduction was defined as >1mm increase in spondylolisthesis comparing follow-up imaging to intraoperative films. PROMs were recorded at the preoperative and follow-up time points. Fusion was assessed 1-year postoperatively via CT. RESULTS A total of 63 patients and 70 levels were included, with mean age 59.8 years (SD,13.8). Nineteen levels (27.1%) had complete reduction intraoperatively, 40 (57.1%) had partial reduction and 11 (15.7%) had no reduction. Of the 30 levels with loss of reduction (50.8%), 20 (66.7%) occurred by 2 weeks postoperatively and 28 (93.3%) occurred by 12 weeks postoperatively. At 6 months, there were significant differences between those who had loss of reduction and those who did not in VAS back pain (3.0 vs 0.9, p=0.017) and SF-12 PCS (41.5 vs 50.0, p=0.035), but no differences were found between the groups for any instruments at any other time points. The overall fusion rate was 89.5% (34/38) at 1 year postoperatively. There was no significant difference in fusion rate between the loss of reduction (16/18) and no loss of reduction (18/20) groups. Patients with loss of reduction had no difference in reoperation rate (1/28) compared to those without loss of reduction (2/24). CONCLUSIONS While a majority of patients demonstrated reduction intraoperatively, 51% had loss of reduction, most commonly in the acute postoperative period. There were few differences in PROMs between patients who had loss of reduction and those who did not, suggesting that radiographic loss of reduction after MI-TLIF in the setting of degenerative spondylolisthesis may not be clinically meaningful. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.