Supine and Dynamic Extension Radiographs as the Strongest Predictors of Post-operative Alignment in Minimally Invasive Lumbar Spine Surgery

Abstract

Study Design: Institutional review board-approved retrospective cohort study. Objectives: Failure to achieve alignment goals may result in accelerated adjacent segment degeneration and poorer outcomes. In “open” spine surgery, intraoperative tools can fine tune alignment; minimally invasive spine surgery techniques may not allow for this type of intraoperative adjustment. The aim of this study was to identify pre-operative radiographic parameters that accurately predict post-operative alignment after minimally invasive lumbar spine surgery. We hypothesized that pre-operative supine and extension sagittal alignment would predict post-operative standing alignment. Methods: 50 consecutive patients underwent lateral or anterior lumbar interbody fusion with or without percutaneous posterior instrumentation by a single-surgeon. Sagittal alignment parameters were evaluated on pre-operative standing scoliosis radiographs, dynamic radiographs, supine CT scout, and 6-week post-operative standing radiographs. Demographic and perioperative data were analyzed. Results: The mean age was 67.8 years. The mean BMI was 29.7. On average, 3 levels were instrumented (range, 2–6). Surgical time was 4.5 ± 1.8 hours. Following surgery, global lordosis increased from 44.7 ± 17° to 48.6 ± 16° (P =.001). However, there was no significant difference between the pre-operative supine (48.5 ± 15°), pre-operative extension (49.2 ± 18°), or 6-week post-operative standing radiographs (48.6 ± 16°). There were strong correlations between post-operative alignment and pre-operative supine (r =.825) and extension (r =.851) alignment. Conclusions: Our results suggest that pre-operative supine and extension radiographs could be a gold standard for minimally invasive lumbar spine surgery alignment correction as they predict post-operative alignment. The extension alignment was the strongest predictor of post-operative alignment.