Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P41. Agreement of degenerative spondylolisthesis definitions on standing and supine lateral radiographs in consecutive patients

BACKGROUND CONTEXT Clinical guidelines recommend standing lateral radiographs as the most appropriate imaging for detecting degenerative spondylolisthesis. However, direct comparison on definitions of spondylolisthesis on standing and supine lateral radiographs in the same patients are lacking. PURPOSE To determine the extent of agreement on commonly used definitions of degenerative spondylolisthesis on clinically obtained standing and supine lateral radiographs among the same patients. STUDY DESIGN/SETTING Cross-sectional study in new patients presenting to the Oregon Health u0026 Science University Spine Center with chief complaint of back pain or radiculopathy. PATIENT SAMPLE Consecutive new patients from 2010 to 2016, age ≥40years, and without a history of prior spinal surgery, vertebral fracture or scoliosis greater than 30°, who were clinically evaluated for degenerative spondylolisthesis. OUTCOME MEASURES Radiographic degenerative spondylolisthesis defined as anterior displacement of ≥3 mm, ≥5 mm and ≥5%. METHODS New patients received standing AP, standing lateral and supine lateral radiographs as a clinical standard. The presence of spondylolisthesis was assessed from L1 to S1. The anterior slip distance (mm) was obtained by measuring the displacement of the posterior surface the superior vertebral body in relation to the posterior surface of the inferior vertebral body. Vertebral body width (mm) was obtained by measuring the narrowest AP diameter of the inferior vertebral body. Percent slip was calculated by dividing the anterior slip distance by the inferior vertebral body width. Kappa statistics were estimated as the measure of agreement on definitions of spondylolisthesis on the pairs of films. RESULTS This study comprised 516 patients (246 (48%) men; 270 (52%) women; mean (sd) age of 60.0 (11) years). Of these, 206 (40%) patients had 239 vertebrae with any anterior displacement of ≥3mm. Spondylolisthesis was most often observed at L4-L5 (112 vertebrae) or L5S1 (96 vertebrae). Numbers and percentages of patients classified as without spondylolisthesis on standing radiographs but with spondylolisthesis on supine radiographs for the ≥3 mm, ≥5 mm and ≥5% definitions, respectively, were 4 (1.9%), 2 (1.3%), and 3 (1.4%). Conversely, numbers and percentages of patients classified as without spondylolisthesis on supine radiographs but with spondylolisthesis on standing radiographs for ≥3 mm, ≥5 mm and ≥5% definitions, respectively, were 37 (18.0%), 46 (30.3%) and 32 (14.5%). Kappa statistics for agreement on definition of degenerative spondylolisthesis on the standing and supine lateral radiographs for ≥3 mm, ≥5 mm and ≥5% were, respectively, 0.83, 0.75 and 0.86. CONCLUSIONS From 18% to 30% of patients with radiographically detectable spondylolisthesis were misclassified as without spondylolisthesis by supine radiographs, whereas less than 2% of patients were misclassified as without spondylolisthesis on standing radiographs. Agreement between standing and supine radiographs worsened with progressively larger slip required to define spondylolisthesis. These results in a large consecutive series of new patients support clinical guidelines to use standing lateral radiographs for diagnosis of radiographic degenerative spondylolisthesis.