Biomechanical investigation of spinal cord stress changes following ACAF for different subtypes of cervical OPLL

To investigate the effect of the Anterior Controllable Antedisplacement and Fusion (ACAF) procedure on stress within the spinal cord, nerve roots, and dura mater for different subtypes of cervical ossification of the posterior longitudinal ligament (C-OPLL) during progressive anterior decompression. C2-C7 cervical spine and spinal cord models were constructed based on CT images. Three C-OPLL subtypes (central-plateau, central-beak, and right-beak) were modeled and subjected to simulated ACAF treatment. By simulating the anterior displacement of the vertebral ossification complex, we analyzed the static stress changes in gray matter, white matter, nerve roots and dura mater for different C-OPLL subtypes. During decompression, among the three C-OPLL subtypes, ACAF achieved the most significant spinal cord decompression in the central-plateau type, especially when the encroachment ratio was reduced from 60 to 30%. ACAF produced the greatest reduction in nerve-root and dural stress in the right-beak type of C-OPLL, especially when the encroachment ratio decreased from 60 to 40%. The decompression efficiency for the nerve roots in the right-beak type and for the dura mater in the central-plateau type plateaued when the encroachment ratio was reduced from 60 to 50% and from 40 to 30%, respectively. In the right-beak type of C-OPLL, asymmetric compression generated higher stresses on the ipsilateral side of the spinal cord complex. After continued gradual decompression, the stress values of the spinal complex gradually decreased in all three groups. Our model demonstrates that all three OPLL subtypes achieve effective decompression, although the degree of stress relief varies across anatomical sites (e.g., spinal cord versus nerve roots) in a subtype-specific manner. The model data suggest that as the residual encroachment ratio decreases to approximately 30%, the marginal benefit of further decompression in terms of stress reduction plateaus. It is important to emphasize that this value is solely a biomechanical observation derived from our model, and clinically acceptable thresholds must be determined by integrating the patient’s neurological status and surgical risks.