The Contribution of Paraspinal Sarcopenia on Sagittal Imbalance in Degenerative Kyphosis.

Objective: To investigate the correlation between paraspinal sarcopenia (PS) and sagittal imbalance (SI) in degenerative kyphosis (DK), and to explore the correlation between paraspinal muscle (PSM) function loss and morphology change in DK.

Methods: One hundred thirty-eight patients with DK and 204 with lumbar spinal stenosis (LSS) were enrolled. The spinopelvic parameters and sagittal vertical axis (SVA) were measured. Patients were divided into the sagittal balance (SB, SVA ≤ 5 cm, n = 61) and SI (SVA > 5 cm, n = 77) groups. Sagittal balanced LSS patients were served as control group. PSM function was evaluated by measuring the maximal voluntary exertion (MVE) and endurance time (ET). Magnetic resonance imaging-derived cross-sectional area (CSA) and fat infiltration rate (FI%) of PSM at T10-L5 were normalized to intervertebral disc CSA. Psoas CSA and FI% were calculated at L3-4 disc level. The correlation assessment using Spearman rank correlation coefficient and multiple linear regression. Logistic regression was used to identify the risk factors of SI.

Results: Significantly lower ET, MVE, relative CSA (rCSA) and higher rFI% was found in the SI group than in the SB and control. The PS were correlated with spinopelvic parameters and regional kyphosis, while lack of correlation was found between the rFI% and MVE. Logistic regression and Youden index analysis showed ET < 15.5 seconds, MVE < 1.3 N/kg, and rCSA (L1-5) atrophy to be potential risk factors for SI in DK.

Conclusion: DK patients with SI demonstrate acerbated PS that indicated by significant PSM dysfunction and morphological alterations. We highlight the significance of PSM combined evaluation and revealed that PS plays an indispensable role in the progression of SI, providing novel insights into the underlying sagittal compensatory mechanisms.