Relationships Between Global Shear Vector Components and Paraspinal Muscle Area

Introduction: Degeneration of the paraspinal musculature has been linked to back pain, impaired postural stability, and development of kyphotic deformity. Characterizing the complex interplay between paraspinal muscles and the forces acting on the spine is therefore critical for analyzing and predicting pathologic spinal conditions. The force generated by muscles is a function of the physiological cross-sectional area (pCSA). To this end, the purpose of this study is to explore the correlation between the Global Shear Vector (GSV) force, paraspinal muscle pCSA, and global sagittal alignment.

Methods: This is a retrospective review of adult patients at a single institution with available weight-bearing full spine X-rays and lumbar spine T2-weighted magnetic resonance imaging (MRI). The physiological cross-sectional area (pCSA) of the multifidus (MF), erector spinae (ES), and psoas major were measured individually on the right side of the spine at the L3 level. Analysis of correlation and multiple linear regression between pCSA, GSV force components, and sagittal vertical axis (SVA) was conducted.

Results: A total of 32 patients were included for analysis. Pearson correlation analysis showed significant correlation between Global Shear Vector- Magnitude (GSV-M) and ES pCSA (r=0.442, P = 0.011) and between SVA and ES pCSA (r=0.352, P < 0.048). Multiple linear regression performed with global shear vector- angle (GSV-A) with GSV-M exhibited significant relationships with MF pCSA (R2=0.859, P < 0.001), ES pCSA (R2=0.895, P < 0.001), and PM pCSA (R2=0.820, P < 0.001).

Conclusion : The combination of GSV components (GSV-A and GSV-M), a novel index for measuring the forces experienced by the spine during upright posture, are strongly correlated to the pCSA of paraspinal muscles. Future studies are needed to explore the role of the paraspinal muscles in force management.