Paraspinal muscle injury, atrophy, and postoperative biomechanical burden after spinal fusion: a systematic review of computational biomechanical evidence

Abstract Background Paraspinal muscles contribute to spinal support, segmental control, and postoperative load transfer after spinal fusion. Although paraspinal muscle injury, atrophy, and degeneration are increasingly recognized after spinal surgery, their biomechanical significance after fusion has not been synthesized in a focused review. Methods A systematic review of biomechanical studies was performed according to PRISMA 2020 guidance. PubMed/MEDLINE, Embase, Scopus, and Web of Science were searched through March 2026, supplemented by citation tracking and manual reference screening. Eligible studies investigated spinal fusion and reported direct biomechanical outcomes related to paraspinal muscle injury, atrophy, preservation, or altered muscle mass using computational biomechanical models or other direct biomechanical approaches. Because of heterogeneity in spinal region, fusion procedure, model framework, muscle-related exposure, and outcomes, qualitative synthesis was performed. Results Eight studies met the inclusion criteria. All were computational biomechanical investigations, including finite element, musculoskeletal, or combined musculoskeletal–finite element models. Most studies evaluated lumbar fusion, while one examined cervical fusion after anterior cervical discectomy and fusion. Across the included studies, compromised paraspinal muscle status was generally associated with a less favorable post-fusion mechanical environment, including greater adjacent-segment loading, increased disc or annular stress, higher facet or ligament force, altered muscle-force distribution, and, in some models, increased implant-related stress. Multifidus preservation or better postoperative muscle quality was generally associated with more physiological load transfer. Several models suggested that the cranial adjacent segment may be particularly vulnerable to muscle-related mechanical disturbance. Conclusions Available computational biomechanical evidence suggests that paraspinal muscle condition is an important modifier of post-fusion mechanics. These findings indicate that the consequences of spinal fusion should not be interpreted solely through construct rigidity or fused-level stability. The surrounding muscular support system should be considered in biomechanical interpretation, operative planning, postoperative rehabilitation, and risk assessment.