• Masayuki Miyagi, Gen Inoue, Yusuke Hori, Kazuhide Inage, Kosuke Murata, Ayumu Kawakubo, Hisako Fujimaki, Tomohisa Koyama, Yuji Yokozeki, Yusuke Mimura, Shinji Takahashi, Shoichiro Ohyama, Hidetomi Terai, Masatoshi Hoshino, Akinobu Suzuki, Tadao Tsujio, Sho Dohzono, Ryuichi Sasaoka, Hiromitsu Toyoda, Sumihisa Orita, Yawara Eguchi, Yasuhiro Shiga, Takeo Furuya, Satoshi Maki, Eiki Shirasawa, Wataru Saito, Takayuki Imura, Toshiyuki Nakazawa, Kentaro Uchida, Seiji Ohtori, Hiroaki Nakamura, and Masashi Takaso.
• Department of Orthopaedic Surgery, School of Medicine, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa, 252-0375, Japan. masayuki008@aol.com.
• Eur Spine J. 2022 Jun 1; 31 (6): 1431-1437.

PurposeCorrection surgeries for spinal malalignment showed good clinical outcomes; however, there were concerns including increased invasiveness, complications, and impact on medico-economics. Ideally, an early intervention is needed. To better understand the patho-mechanism and natural course of spinal alignment, the effect of factors such as muscle mass and strength on spinal sagittal imbalance were determined in a multicenter cross-sectional study.MethodsAfter excluding metal implant recipients, 1823 of 2551 patients (mean age: 69.2 ± 13.8 years; men 768, women 1055) were enrolled. Age, sex, past medical history (Charlson comorbidity index), body mass index (BMI), grip strength (GS), and trunk muscle mass (TM) were reviewed. Spinal sagittal imbalance was determined by the SRS-Schwab classification. Multiple comparison analysis among four groups (Normal, Mild, Moderate, Severe) and multinomial logistic regression analysis were performed.ResultsOn multiple comparison analysis, with progressing spinal malalignment, age in both sexes tended to be higher; further, TM in women and GS in both sexes tended to be low. On multinomial logistic regression analysis, age and BMI were positively associated with spinal sagittal malalignment in Mild, Moderate, and Severe groups. TM in Moderate and Severe groups and GS in the Moderate group were negatively associated with spinal sagittal malalignment.ConclusionAging, obesity, low TM, and low GS are potential risk factors for spinal sagittal malalignment. Especially, low TM and low GS are potentially associated with more progressed spinal sagittal malalignment. Thus, early intervention for muscles, such as exercise therapy, is needed, while the spinal sagittal alignment is normal or mildly affected.© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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