Benefits of Steroid Injections into Paraspinous Muscles After Spinal Surgery in a Rat Paraspinal Muscle Retraction Model

Open posterior lumbar surgery involves detaching paraspinal muscles from the spine to decompress neural tissues and to place instruments. While this operation improves the quality of life, it often has adverse effects on skeletal muscles like inflammation, degeneration, and fibrosis. Corticosteroids are well known for their anti-inflammatory function. In this study, we assessed the protective effects of intramuscular injection of corticosteroid on injured paraspinal muscles following surgery on the spine. C2C12 cells were co-exposed to hypoxia and lipopolysaccharide (LPS) to simulate ischemia and inflammatory response after muscle retraction to assess the effect of steroid. In vivo experiment, animals first underwent paraspinous muscle splitting with retractors to induce muscle injury, and later were assessed for neurobehavior, electrophysiology, and protein level related to inflammatory or regeneration following intramuscular (IM) steroid injection. Steroid rescued reduced cell viability caused by hypoxia + LPS, and attenuated induced protein expression of iNOS, COX2, Bad, and Bax. In neurobehavioral assessments (CatWalk, Ethovision, Von Frey test, and open field locomotor), retraction of paraspinous muscles worsened behaviors that were improved by IM steroid injections. The electrophysiology study showed that IM steroid injection lessened the muscle denervation caused by retraction. Similarly, IM steroid injections also attenuated dorsal root ganglion antigenicity of CGRP, Iba-1, and CD68 induced by muscle retraction. Muscle retraction downregulated AChR, desmin, PSD 95, and GAP 43, whereas IM steroid injection attenuated the adverse effects. The restoration of muscle morphology and decreased fibrosis were also facilitated by IM dexamethasone. IM steroid injection appears to protect against retraction damage in paraspinous muscle following spinal surgery. IM steroid paraspinous muscle injection may provide beneficial effects in spinal operations.