INTRODUCTION: This study aimed to assess the impact of midline lumbar fusion with cortical bone trajectory screws (MIDLF/CBT) on the multifidus muscles, focusing on the evaluation of their postoperative atrophy. CLINICAL RATIONALE FOR THE STUDY: MIDLF/CBT is a relatively new technique increasingly used to treat spinal instability. Despite its reduced invasiveness compared to traditional posterior lumbar interbody fusion with traditional pedicle screws (PLIF/TP), concerns remain about potential damage to the multifidus muscles that are crucial for spinal stability. Understanding the extent of muscular atrophy post-MIDLF/CBT is vital for improving surgical outcomes, and potentially patient rehabilitation strategies. MATERIAL AND METHODS: This study retrospectively analysed preoperative and postoperative MRI scans of patients who underwent MIDLF/CBT for degenerative segmental spondylolisthesis. The bilateral width of the multifidus muscles at the operated segment and adjacent segments was measured using axial T2-weighted MRI scans. Statistical comparisons were made using a paired t test, with significance set at p < 0.05. RESULTS: The study included 16 patients with an average age of 57 ± 10 years, 10 of whom (62.5%) were women, and featured a mean follow-up period of 37 ± 25 months. Postoperative measurements showed a significant reduction in the width of the multifidus muscles at the operated segment (mean difference -3.3mm, p = 0.02) and the inferior adjacent segment (-7.4 mm, p < 0.01). A decrease in muscle width at the superior adjacent segment was also observed, although this was not statistically significant. CONCLUSIONS AND CLINICAL IMPLICATIONS: Our study concluded that MIDLF/CBT results in significant multifidus muscle atrophy at and below the operated segment, potentially impacting postoperative rehabilitation and recovery. These findings highlight the need for further research comparing MIDLF/CBT to other spinal stabilisation techniques. Additionally, incorporating functional electromyographic assessments of paraspinal muscles could provide deeper insights into the long-term consequences of spinal surgeries and helpdevelop new approaches and strategies to mitigate paravertebral muscles atrophy, thus enhancing patient outcomes.

3rd Faculty of Medicine Charles University Prague Czech Republic

Clinic of Anaesthesiology and Resuscitation University Hospital Kralovske Vinohrady Prague Czech Republic

Department of Neurosurgery Tomas Bata Regional Hospital Zlin Czech Republic

Department of Rehabilitation and Sports Medicine Faculty of Medicine University of Ostrava Ostrava Czech Republic

Neurosurgical Clinic University Hospital Kralovske Vinohrady Prague Czech Republic

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