Effect of ACAF and posterior LAMP on the facet joint and adjacent intervertebral disc in the treatment of cervical OPLL: a finite element analysis

Background: Cervical ossification of the posterior longitudinal ligament (OPLL) is a pathological condition where ligament ossification compresses the spinal cord or nerve roots, resulting in sensory, motor, and autonomic dysfunctions. This study aims to clarify the biomechanical distribution of two surgical interventions—the newly proposed Anterior Cervical Corpectomy and Fusion (ACAF) and the traditional Laminoplasty (LAMP)—using three-dimensional finite element analysis. Methods: A high-fidelity, full cervical spine model was reconstructed based on CT scans of a healthy male volunteer. On this foundation, a preoperative OPLL model involving the C4, C5, and C6 segments was established. Subsequently, two postoperative models (ACAF and LAMP) were created. To simulate physiological loading, a 50N axial force and a 1.0N·m moment were applied to the C1 superior surface. The study analyzed the Range of Motion (ROM) and stress distribution on facet joints, adjacent C2/3 intervertebral discs, and endplates under six conditions: flexion, extension, bilateral bending, and bilateral rotation. Results: Postoperative models for both ACAF and LAMP exhibited a decrease in cervical ROM compared to preoperative states, with the reduction being significantly more pronounced in the ACAF model. Biomechanically, ACAF demonstrated lower stress levels on the facet joints, adjacent segment discs, and both upper and lower cartilaginous endplates than the LAMP model. However, specific regional stresses were higher in the ACAF group; notably, the annulus fibrosus experienced greater stress during flexion, extension, right lateral bending, and left rotation. Additionally, stress on the nucleus pulposus in the ACAF model exceeded that of the LAMP model during extension and right lateral bending. Conclusion: This FEA study indicates that while ACAF more substantially limits cervical mobility, it effectively reduces average stress on vertebral bodies, facet joints, and adjacent segments compared to LAMP. These findings suggest that ACAF may offer a biomechanical advantage in reducing long-term postoperative pain or recurrence driven by mechanical stress changes.