Type Id versus type IId three-level hybrid surgery for the treatment of noncontiguous cervical spondylosis: A finite element analysis

The objective of the research is to simulate different forms of three-level hybrid surgeries, aiming to establish a foundational reference for the selection of suitable treatment strategies for multilevel noncontiguous cervical degenerative disease (CDD). For the development of precise finite element models (FEMs), this study utilized computed tomography (CT) data. Two cross-segment surgical approaches were primarily investigated: C3/4 cervical disc arthroplasty (CDA), C5/6 anterior cervical discectomy and fusion (ACDF), and C6/7 ACDF in the type Id model; C3/4 CDA, C5/6 CDA, and C6/7 ACDF in the type IId model. The follower load technique was employed to apply an initial axial load of 73.6 N at the motion center. Subsequently, a moment of 1.0 Nm was introduced at the center of the C2 vertebra to simulate the overall motion of the model. In contrast to type IId, type Id exhibited lower average intervertebral disc pressure in C4/5 across various motions. The average intervertebral disc pressure in C2/3 was higher in type Id compared to type IId in flexion and axial rotation, whereas the reverse was observed in lateral bending. Type IId exhibited notably lower facet joint contact stresses during extension in C2/3 and C4/5 when compared to type Id. Type Id has a better protective effect on IS, and can significantly reduce the average pressure of the intervertebral disc in IS compared with type IId. Type IId has a significant protective effect on the post-column structure of non-fused segments.