Paraspinal Muscle Parameters Predict Postoperative Sagittal Balance in Cervical Disc Arthroplasty: A Structural Equation Model Analysis.

Study design: Retrospective analysis.

Objective: To identify the associations between preoperative paraspinal muscle parameters and postoperative outcomes following cervical disc arthroplasty (CDA), while screening for predictors.

Summary of background data: Paraspinal muscles play a critical role in maintaining cervical alignment, significantly contributing to cervical mobility and stability. To date, there is limited evidence regarding the impact of paraspinal muscles on CDA.

Methods: This study included 185 patients who underwent single-level CDA. Preoperative paraspinal muscle parameters, including fatty infiltration (FI), cross-sectional area ratio (CSA r), and muscle asymmetry (ASY%), were assessed using MRI. Correlation analysis was employed for preliminary screening. Finally, structural equation modeling (SEM) was employed for comprehensive analysis.

Results: Paraspinal muscle degeneration was prevalent in this cohort, with a higher proportion of moderate to severe FI (Goutallier Grade > 2) from the cranial to caudal levels. According to the correlation analysis, at the final follow-up, cervical lordosis was most strongly correlated with CSA r at C4/5 ( P =0.010); SVA was most related to CSA r at C5/6 ( P =0.030); and the T1 slope was associated with CSA r at C4/5 ( P <0.001), C5/6 ( P <0.001), as well as at the surgical level ( P <0.001). Moreover, a positive correlation was observed between preoperative pain scores and FI ( P =0.035). However, no such correlation was identified in the postoperative period. Comparative analysis of SEMs across different muscle variables revealed variations in predictive factors for postoperative sagittal balance parameters, with CSA r emerging as the significant contributor ( P =0.019, Estimate=0.176), rather than FI or ASY%.

Conclusions: Compared with postoperative clinical outcomes, mobility, and prosthesis stability, preoperative muscle parameters were most correlated with sagittal balance after CDA. Specifically, CSA r outperformed in predicting postoperative sagittal balance. These findings suggest CDA may be associated with an elevated risk of sagittal imbalance when performed on patients with significant preoperative muscle degeneration.

Level of evidence: 3.