The comparative impact of body mass index on outcomes following minimally invasive versus open surgery for grade 1 spondylolisthesis: 2-year follow-up from the Quality Outcomes Database.

Abstract

ObjectiveBoth minimally invasive (MI) and open surgical approaches can be effective for the treatment of degenerative lumbar spondylolisthesis (DLS). However, comparative effectiveness might be influenced by body mass index (BMI). The authors aimed to determine if there is a differential impact of open versus MI approaches on patient outcomes based on BMI.MethodsThe authors performed a retrospective analysis of the prospective Quality Outcomes Database, identifying patients surgically treated for grade 1 DLS between July 2014 and June 2016. BMI was dichotomized into 2 groups: nonobese (BMI < 30 kg/m2) and obese (BMI ≥ 30 kg/m2) in accordance with the Centers for Disease Control and Prevention definition. The primary outcome was a minimal clinically important difference (MCID) in the Oswestry Disability Index (ODI). Secondary outcomes included an MCID in the EQ-5D, the North American Spine Society patient satisfaction index, an MCID in the numeric rating scale for leg pain (NRS-LP) and back pain (NRS-BP), surgical complications, discharge disposition, and reoperation. These variables were compared between surgical approaches and after subgrouping by BMI group. A nonroutine discharge was defined as discharge to any location other than home.ResultsSix hundred eight patients with grade 1 DLS were identified. Five hundred seventeen (85%) had 2-year follow-up for the primary outcome. There were 285 nonobese and 232 obese patients, and 216 patients underwent an MI approach and 301 underwent an open approach. Four hundred two patients (77.8%) underwent instrumented fusion, whereas 115 (22.2%) underwent decompression alone. Instrumented fusion was performed more frequently in the open group (81.7% vs 72.2%, χ2 = 6.03, p = 0.014) and in obese patients (83.6% vs 73.0%, χ2 = 7.76, p < 0.01). Regardless of surgical approach or BMI, 2-year (2Y) ODI (mean difference [MD] -23.4 ± 20.38, p < 0.001), NRS-LP scores (MD -3.81 ± 3.82, p < 0.001), and NRS-BP scores (MD -3.32 ± 3.43, p < 0.0001), and EQ-5D scores (MD 0.21 ± 0.24, p < 0.0001) improved from baseline. Among obese patients, the proportion attaining an MCID in 2Y ODI (73.3% vs 56.34%, χ2 = 6.11, p = 0.013) and EQ-5D (53.33% vs 37.32%, χ2 = 4.32, p = 0.038) was larger after MI than after open surgery; however, no differences were seen between MI and open surgery in the nonobese patients. There were no differences between MI and open approaches in either BMI group for the remaining secondary outcomes.ConclusionsRegardless of approach, patients improved following surgery for grade 1 DLS. Patients with BMI ≥ 30 kg/m2 had better long-term outcomes when treated with an MI surgical approach versus open surgery. This difference in outcomes between MI and open surgery was not observed among patients with BMI < 30 kg/m2.