Temporal Observations of Multifidus Muscle Injury and Degeneration Following Posterior Thoracolumbar Spine Surgery: A Clinical Histological Study over a Three-Year Time Period.

INTRODUCTION: To determine the consequences and potential mechanisms of injury to the multifidus muscle associated with surgery using the conventional thoracolumbar posterior approach.

METHODS: Patients were categorized into three groups based on the duration of time since their initial thoracolumbar fracture surgery: a 1-year postoperative group, a 2-year postoperative group, and a 3-year postoperative group. All patients required removal of internal fixation between May 2023 and June 2024. For each group, we performed morphometric analysis of the multifidus muscle using digital images, and muscle samples were subjected to histological analysis.

RESULTS: Digital photography indicated a significant temporal reduction in the proportion of muscle within the multifidus muscle, exhibiting a significant change over time (p<0.0001). Hematoxylin and eosin staining of histological samples revealed varying degrees of steatosis in the postoperative multifidus muscles; prolonged intervals following internal fixation surgery were associated with more pronounced fat infiltration. Analysis of the multifidus fibrosis using Masson's staining demonstrated that muscle fibers subjected to paravertebral muscle dissection surgery exhibited a tendency towards fibrosis, which increased over time. Reduced vessel density, defined by CD31 expression, was observed at all follow-up times, and the number of nerve fibers decreased significantly with increasing time post-surgery.

CONCLUSIONS: Over time, the multifidus muscle exhibited obvious fibrosis and steatosis following traditional posterior thoracolumbar surgery. Our analyses suggest that the mechanism involved could be related to reduced angiogenesis and denervation.