Presurgical MRI-based assessment of paravertebral muscles in patients with spinal stenosis

Background. The successful surgical management of spinal stenosis depends on a comprehensive preoperative evaluation, including the assessment of paravertebral muscle health. Despite the pivotal role of these muscles in supporting the spine and facilitating post-surgical recovery, their condition is frequently overlooked in standard pre-surgical assessments. This article underscores the importance of utilizing magnetic resonance imaging (MRI) to evaluate the paravertebral muscles’ integrity before surgery. Proposed methods and data could contribute to better surgical prognoses and elevate the quality of life for patients undergoing surgery for spinal stenosis.

Aim. To study the possibilities of using the index of fat replacement developed by us to evaluate condition of the paravertebral muscles and to analyze its objectivity compared to quantitative calculation of fat fraction in the muscles (M. Gloor et al.) per MRI data, to identify the optimal study level to perform the abovementioned evaluation.

Materials and methods. Data were acquired from 16 patients with symptomatic spinal canal stenosis (average age 43 years, an equal number of men and women) who underwent MRI on a Siemens Magnetom Prisma 3T scanner. Special attention was paid to evaluating the area and fatty infiltration of the paravertebral muscles using a three-dimensional axial T1 gradient echo sequence and the Dixon technique for fat suppression. Images assessment was performed using the InobitecPro software, where the muscles signal intensity and area was measured, and the fat fraction index and fat replacement index were calculated. Statistical analysis was performed using Statistica version 8.0 software, allowing for an objective assessment of the degree of fatty infiltration in the paravertebral muscles in patients with spinal canal stenosis.

Results. Qualitative analysis of images showed consistently visible attachment of fascia to the facet joint at the L₄ level, unlike at L₅ and L₃ levels. Additionally, the varying curvature angles of lumbar lordosis affected the complete inclusion of the spinous process on axial plane at L₅ and L₃ levels, complicating standardized data collection. Histograms constructed to determine the optimal measurement level showed the least variation in the fat replacement index at L₄ among patients. Spearman’s correlation analysis revealed a significant positive relationship (ro = 0.74, p <0.05) between proposed fat replacement index and fat fraction values. Linear graphs for these variables clearly demonstrated that with an increase in muscle fat fraction, the accuracy of the fat replacement index improves, being least precise at lower fat fractions.

Conclusion. The obtained data show potential benefit of including axial T1-weighted images parallel to the inferior endplate of the L4 vertebra and calculation of the proposed index of fat replacement into preoperative MRI protocol. However, to determine the possibility of using the index of fat replacement as a prognostic factor, it must be studied dynamically in a large patient sample.

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