The current study aims to evaluate paraspinal muscle morphology in patients with lumbar spinal stenosis (LSS) and degenerative spondylolisthesis (DS) and to create a mathematical model of the spine and determine possible gender and diagnosis-specific characteristics. The analysis included 24 patients who had DS and 27 patients who had a LSS. Transversal sections of conventional MRI T2-weighted images from L3 to S1 were used to measure the cross-sectional area (CSA) and fatty infiltration of the psoas (PS), erector spinae (ES), and multifidus (MF). In the second part, the sagittal spine radiographs of 42 patients with LSS and/or DS and 21 radiologically normal subjects, were obtained. With a mathematical model based on minimizaing the elastic bending energy of the spine, we determined two parameters that characterize the curve of the spine. Comparison of summed muscle CSA at L3-L4, L4-L5, and L5-S1 between genders revealed that male patients had considerably higher normalized CSA of PS and lower normalized CSA of ES, while the difference in MF was not statistically significant. After adjustment, it turned out that the diagnosis of DS was an independent predictor of higher ES CSA, but not of PS or MF. The correspondences of geometric and biomechanical parameters and sagittal balance were tested and, only the cLS and CI model parameters showed a statistically significant correlation with sagittal balance (SVA/SFD). The SVA/SFD parameter was significantly different between the patients and normal subjects. Females with LSS and LSS with DS exhibit hypotrophy of the PS and hypertrophy of the ES muscle in comparison to male patients with the same disease. Patients with LSS and DS have hypertrophy of ES muscle compared to patients with LSS alone. The model provides a possibility to predict changes in the thoracolumbar spine shape in surgery planning and the assessment of different spine pathologies.
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