Sarcopenia Among Adults with Spinal Deformity Undergoing Correction

Introduction: A common cause of spinal deformity in older populations is degenerative scoliosis. Psoas index (PSI) has had mixed results as a prognostic tool. Studies have referenced average PSIs of 5.89 +/- 1.51 cm^2/m^2 for healthy males over 60 years and 4.22 +/- 0.98 cm^2/m^2 for healthy females over 60 years. We sought to verify if PSI was related to complications post-operatively.

Methods: We reviewed radiographic/outcome data of 116 thoracolumbar fusion patients over 65 years between 2015 and 2024. Pre-operative PSI was calculated as averaged bilateral surface area of the psoas at L3, visible by axial imaging, divided by height^2.

Results: Our cohort included 79 females (68.1%). Average age and BMI were 70.9 + 4.3 years and 28.9 + 5.4. 12 patients (10.3%) developed proximal junction failure (PJF) and 32 (27.6%) reported persistent back pain.
The average PSI was 6.10 +/- 2.01 cm^2/m^2. Average PSI for males was 7.32 +/- 1.92 cm^2/m^2 (p < 0.001 compared to healthy) and 5.62 +/- 1.70 cm^2/m^2 for females (p < 0.001 compared to healthy).

Among males, no significant differences in PSI were found when grouped by development of PJF (7.38 no-PRF vs 7.04 PRF, p=0.67) or back pain (7.19 no back pain vs 8.15 back pain, p=0.16).

Among females, no significant differences in PSI were found when grouped by back pain (5.73 cm^2/m^2 no back pain vs 5.34 cm^2/m^2 back pain, p=0.32). Significant differences were observed when grouped by PJF (5.72 cm^2/m^2 non-PJF vs 4.28 cm^2/m^2 PJF, p=0.01). Univariate regression revealed a PSI risk ratio of 0.55, but with p=0.07.

Conclusion : PSI was greater in this study than age-matched healthy adults, which is reflective of a strict patient surgical selection criterion. Despite low clinical sarcopenia rates, decreased PSI was correlated to PJF, suggesting general sarcopenia to be predictive of mechanical failure. A similar trend was observed in males, but without sufficient statistical power. More attention should be directed to evaluating spinal sarcopenia in spinal deformity to better classify the connection between global sarcopenia and spinal deformity.