Measuring multifidus muscles atrophy after midline lumbar fusion with cortical bone trajectory screws due to spinal instability and spondylolisthesis: a retrospective case series

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.