Friday, September 28, 2018 1:00 PM–2:30 PM abstracts: a new look at imaging: 210. Severe lumbar disability is associated with decreased psoas cross sectional area in degenerative spondylolisthesis

Abstract

BACKGROUND CONTEXT There has been increasing interest in examining the relationship of lumbar paraspinal muscle morphometry and outcomes after lumbar spinal surgery, as well as investigating any association between changes in paraspinal muscle density and low back pain.However, the relationship of the iliopsoas muscle to the posterior paraspinal muscles, and the effect of variation in psoas cross sectional area to lumbar disability in patients with degenerative spondylolisthesis, has not been extensively explored. PURPOSE We set out to compare the absolute psoas and paraspinal CSA in patients with degenerative lumbar spondylolisthesis and corresponding severe disability to similar patients with only mild or moderate disability. STUDY DESIGN/SETTING Retrospective cohort. PATIENT SAMPLE Inclusion criteria were any patient undergoing single level lumbar fusion for degenerative spondylolisthesis greater than 18 years of age at one institution, based on the ICD-9 code 721.42, with a preoperative lumbar spine MRI and completed preoperative patient-reported outcome scores. Patients under the age of 18 years, those lacking a preoperative lumbar spine MRI or completed preoperative patient-reported outcome scores, or those with a diagnosis other than degenerative lumbar spondylolisthesis were excluded from the study. METHODS We retrospectively reviewed the medical records of 101 patients undergoing lumbar fusion for degenerative spondylolisthesis. Patients were divided into Oswestry Disability Index (ODI) score 40 (severe disability, SD) groups. The total CSA of the psoas and paraspinal muscles were measured on preoperative magnetic resonance imaging (MRI). Student's t-test was used to compare continuous variables between groups. Multivariable logistic regression was performed analyzing the effects of ASA class, history of heart disease, smoking status and psoas CSA on lumbar disability. P RESULTS There were 37 patients in the SD group and 64 in the MMD group. Average age and body mass index were similar between groups. For the paraspinal muscles, average iliocostalis CSA was 1093.5mm2 versus 1192.2mm2 for the SD group versus the MMD group, respectively (p=.168). Similarly, the longissimus CSA was 685.8mm2 versus 764.8mm2 (p=.329), respectively, and the multifidus CSA was 499.1mm2 versus 526.0mm2 (p=.125), respectively. Psoas muscle CSA was significantly decreased in the SD group compared to the MMD group (1010.08mm2 vs. 1178.6mm2, p=.041). Multivariable logistic regression demonstrated that active smoking was independently associated with severe disability (OR=12.9, range: 1.19–140.2, p=.035), while psoas size in the upper quartile was significantly protective against severe disability (OR=0.13, range: 0.03–0.66, p=.013). CONCLUSIONS In patients with severe lumbar disability and a diagnosis of degenerative spondylolisthesis, when compared to similar patients with mild or moderate disability, we found significantly decreased absolute cross sectional area of the psoas muscle. In addition, multivariate analysis found that increased psoas CSA was significantly protective against severe lumbar disability. Our findings are suggestive of a potential association between psoas atrophy and worsening severity of lumbar disability.