Impact of different paraspinal muscle mass on the prognosis of ACDF-a finite element analysis.

Introduction: Cervical spondylotic myelopathy (CSM) is a common degenerative disease of the cervical spine, for which anterior cervical discectomy and fusion (ACDF) serves as an effective surgical treatment. Recent studies have suggested that the quality of the paraspinal muscles, particularly the multifidus muscle, is closely related to postoperative outcomes; However, biomechanical evidence remains limited. The aim of this study is to investigate the biomechanical impact of varying paraspinal muscle mass on the cervical spine following ACDF. Methods: A finite element model of the cervical spine, including vertebrae, intervertebral discs, ligaments, and implants (cage and screws), was developed based on CT data from a healthy volunteer. Three models simulating different postoperative states of the multifidus muscle were constructed: a postoperative muscle training model (120% muscle quality), a postoperative muscle atrophy model (80% muscle quality), and a control model (100% muscle quality). Flexion, extension, lateral bending, and rotational loads were applied to each model to analyze changes in adjacent segment disc pressure, implant stress distribution, capsular ligament stress, and range of motion (ROM). Results: In the finite element models of different muscle quality groups after ACDF, the muscle atrophy model (80% muscle quality) showed a general increase in the intervertebral disc pressure of adjacent segments, especially during flexion-extension movements, which indicates an elevated risk of degeneration. Meanwhile, the stress values of implants such as cages and screws were increased, with more significant elevation observed during flexion and rotation. The capsular ligament stress was also elevated in the muscle atrophy model, and load overload was prone to occur during extension and rotation. In addition, muscle atrophy could lead to an increase in the ROM of adjacent segments. In contrast, all biomechanical indices of the muscle exercise model (120% muscle quality) were superior to those of the normal model. Conclusion: Paraspinal muscle quality is a critical factor influencing biomechanical stability after ACDF. Muscle atrophy may increase the risk of adjacent segment degeneration and implant failure, while muscle strengthening contributes to enhancing postoperative stability. These results support that preoperative evaluation of paraspinal muscle status and targeted postoperative muscle strength training hold significant clinical implications for improving surgical prognosis.