Characteristics of the psoas minor muscle in modeling lateral interbody spondylodesis of the lumbar spine

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ВACKGROUND: For the treatment of degenerative diseases of the spine, various deformities, a minimally invasive technique of lateral lumbar interbody fusion is used, which minimizes the risks of spinal cord injury. In the development of these pathologies, the most important role is assigned to the paraspinal muscles, the histological features of which are insufficiently elucidated in the relevant literature when modeling spondylodesis.
 АIM: To investigate the effect of lateral interbody vertebral fusion (spondylodesis) when introducing titanium implants on the histostructure of the psoas minor muscle.
 МATERIALS AND METHODS: Experiments were performed in 14 mongrel dogs, 3 individuals the control group (norm). The аnimals underwent discectomy at the level of L45, L56 vertebrae through the lateral approach on the right, and interbody titanium implants were installed. The lumbar spine was stabilized with an external fixator for 30 days. Paraffin muscle sections were stained with hematoxylin-eosin, according to Masson.
 RESULTS: During the experiment, an increased variety of myosymplast diameters, loss of polygonality of their profiles, fibrosis of the interstitial space, and sclerotization of the vascular membranes were observed in the psoas minor muscle. The volume density of endomysium in both muscles increased 1.5 times relative to the norm after 6 months Other parameters decreased: the volume of myosymplasts was 95%, that of microvessels 73% on the left, 83% on the right. On the other hand, the degree of fatty infiltration increased, amounting to 276% on the left and 394% on the right of the normal parameters. After 18 months, the bulk density of muscle fibers on the left was restored to the value in the control, on the right it was only 95%. The degree of sclerotization in the muscle on the left is 133%, on the right 161% of the norm; the index of fatty infiltration was 146% on the left and 339% on the right of the normal parameter.
 CONCLUSION: pathohistological changes in the psoas minor during lateral interbody fusion are more pronounced on the side of the operative approach, which necessitates minimizing trauma to the paravertebral muscles during operations in order to prevent sclerotization and fatty involution of muscle tissue.