Spinal Sarcopenia: A Narrative Review of the Current Limitations in Its Application in Spinal Deformity

Introduction: Sarcopenia, characterized by the age-related decline in skeletal muscle mass and strength, is variably associated with adverse outcomes in adult spinal deformity (ASD). This condition complicates ASD management due to risks of postoperative complications. As sarcopenia becomes a more prominent prognostic tool, its application in ASD is limited by variability in its definition and measurement. Recent studies have further separated classification of sarcopenia into two main categories within spine surgery: 1) general sarcopenia assessing systemic muscle degeneration and 2) spine-specific sarcopenia assessing muscle degeneration within localized paraspinal musculature. In 2023, the Scoliosis Research Society (SRS) established a task force to address these challenges and optimize outcomes for ASD patients with sarcopenia. This task force also sought to evaluate the effectiveness of using general and spine-specific sarcopenia metrics for prognostication.

Methods: The SRS task force evaluated the relationship between sarcopenia and surgical outcomes in ASD, explored methods for assessing sarcopenia, and provided recommendations for managing ASD patients with consideration of sarcopenia based on literature review. Global and spine-specific sarcopenia assessment approaches were compared, emphasizing the impact of diagnostic methods, such as MRI and clinical performance tests, on outcome prediction.

Results: The large variability in sarcopenia measurement methods significantly affected its prognostic utility in ASD treatment. For instance, studies using psoas muscle cross-sectional area to define global sarcopenia revealed mixed results regarding surgical complications. Additionally, assessments focusing on fatty infiltration of paraspinal muscles show stronger correlations with complications like proximal junctional kyphosis (PJK) than generalized sarcopenia markers. Spine-specific sarcopenia metrics, including lumbar multifidus and erector spinae measurements, may better predict outcomes in deformity correction.

Conclusion : Standardizing sarcopenia assessment in ASD is essential to improve its prognostic accuracy and facilitate integration into clinical decision-making. Future studies should refine sarcopenia metrics for spine-specific sarcopenia as opposed to general sarcopenia. Research should also be done to optimize interventions, such as resistance training and nutritional supplementation, to potentially enhance surgical outcomes. Adopting consistent, targeted sarcopenia evaluation can contribute to safer, more effective treatment pathways for ASD patients.