The Impact of Sarcopenic Obesity on Adjacent Segment Disease and Mechanical Complications Following Degenerative Lumbar Fusion

Introduction: Sarcopenia has been associated with morbidity following spine surgery; the majority of past studies focus on frailty through purely volumetric assessment and not muscle composition. Obesity is a known factor for complications, but the relationship between muscle volume and fat composition (sarcopenic obesity) has not been studied. This study aims to study relationship of paraspinal muscle sarcopenia to adjacent segment disease (ASD) and mechanical complications.

Methods: We retrospectively reviewed adult patients who had lumbar fusion for degenerative disease between 2014-2016. At the L3-4 disc space, sarcopenia was assessed using the paraspinal muscle index (PMI) and Goutallier classification (GC) (qualitative assessment of fat content), respectively. Body mass index (BMI), PMI, and GC grading compared adjacent segment disease and mechanical complications at two-year follow-up with CT imaging.

Results: A total of 184 patients were included. Mean age was 66.0 years and 58.2% were female. Mean 3.6 segments were fused, and BMI was 29.1. Across GC grades, similar BMI was observed (p=0.681), but significantly higher GC grades were seen with older age (p < 0.001). PMI was highly associated with BMI with greater BMI having greater PMI, p=0.010). There were no differences in smoking, osteoporosis, interbody use, and BMP among grades for each classification. 14.1% exhibited radiographic mechanical complications: hardware failure (10.8%), pseudoarthrosis (7.6%). Overall, 9.8% needed revision for these mechanical complications. 40.0% demonstrated radiographic ASD and overall, 18.9% required extension of fusion. Higher GC grades was significantly associated with mechanical complications (3.2% to 62.5%, p=0.001) and revision (20.6% to 62.5%, p=0.006). PMI was not a predictor of ASD and complications, but higher BMI was significant associated with higher incidence of ASD (p < 0.001).

Conclusion : Sarcopenic obesity, a measure of muscle content, is a more important measure of long-term outcomes with higher GC grade at risk for complications (compared to PMI or BMI). Additional studies are warranted but preoperative risk assessment should consider sarcopenic obesity.