General Session: MIS - Hall F
Presented by: E. Marigi
E. Marigi(1), S. Yson(1), J. Sembrano(1)
(1) University of Minnesota, Orthopaedics, Minneapolis, MN, United States
Purpose: To date, it is not quantifiably known whether the volume of disc removed correlates with endplate surface prepared, and more importantly there have been no clinical studies to validate the relationship between amount of disc removed and fusion success rates or clinical outcomes. Therefore, the goal of this study was to identify a correlation between disc volume removed (DVR) during MIS lateral lumbar interbody fusion (LLIF), clinical outcomes (Oswestry Disability Index or ODI), and successful arthrodesis rates.
Methods: Single institution, single surgeon retrospective study from 2008 to 2016. During surgery, volume of disc material removed per level was measured and recorded. Patients were followed at post-operative intervals of 6 weeks, 3 months, 6 months, 1 year and 2 years where patients filled out clinical outcome questionnaires: Visual analog scale (VAS) pain scores and ODI. At 1 year post-op a lumbar CT for fusion assessment was obtained, repeat scans were later obtained if fusion was not yet deemed solid at that time. Fusion status per level was graded using the system: A = definitely fused; B = probably fused / maturing; C = probably not fused / locked pseudarthrosis; D = not fused without loose fixation; E = not fused with loose fixation. Statistical analyses were performed in order to assess relationships between: (a) fusion rate and ODI at 1 year; (b) fusion rate and ODI change (baseline to 1 year); (c) DVR and fusion rate; (d) DVR and ODI at 1 year; and (e) DVR and ODI change.
Results: 94 patients (86 males and 8 females) at a total of 140 levels. The average age was 64 years (37 - 88). Baseline back pain VAS = 6.85 ± 1.34, leg pain VAS = 6.18 ± 1.92, and ODI = 58 ± 14.36. Fusion grades were mostly A (63) or B (41), with 1 C, 0 D, and 1 E. The mean DVR per level was 9.5 ml (3.2 - 27.0). The mean DVR among fusion grades were: grade A = 9.7 mL, grade B = 8.8 mL, and Gr C/E = 8.3 mL. For the analysis, we considered grade A vs. all other grades (B, C, E). There were no statistically significant correlations found for all relationships analyzed: a (p = 0.13), b (p = 0.14), c (p = 0.21), d (r = -0.17) and e (r = 0.013). There was a considerably worsened 1 year ODI among patients with Grade A fusion status (42%) vs Grade C (53%), but this did not reach statistical significance (p=.06).
Conclusion: Our study was unable to demonstrate a significant correlation between the volume of disc removed intraoperatively with either fusion success rate or patient-reported surgical outcomes. This may be due to disc volume removal only being one important step in the overall process of obtaining a solid fusion. Study limitations include its retrospective nature, a relatively small sample size leading to a low number of pseudarthrosis, and other factors that may affect outcome such as sagittal alignment parameters. The next step in our analysis includes expressing disc volume removed as a percentage of the preoperative disc volume, a more representative measurement.