Biomechanical evaluation of a novel cervical interfacet self-locking cage versus ACDF: a goat cadaveric study combined with human CT-based finite element analysis

BACKGROUND: Anterior cervical discectomy and fusion (ACDF) is a well-established treatment for cervical degenerative disease (CDD). Nevertheless, its anterior approach carries inherent risks to critical neck structures, prompting the exploration of posterior fusion alternatives for selected patients. Traditional anterior cervical discectomy and fusion (ACDF) for cervical degenerative disease involves navigating complex anterior neck anatomy with potential risks to critical neurovascular structures, motivating the development of safer posterior fusion alternatives. METHODS: Twenty-four fresh C5-C6 segments from adult goats were randomly assigned to the intact, ACDF, and CILC groups (n = 8 per group). After confirming the anatomical similarity between goat and human cervical spines via three-dimensional reconstruction, corresponding surgical procedures were performed at the C5-C6 level. Range of motions (ROMs) in flexion-extension, lateral bending, and axial rotation were measured under a pure moment of 1.5 N·m using a material testing machine. A finite element model of C3-C7 was developed based on computed tomography data from healthy adults. ACDF and CILC procedures were simulated, with a 1 N·m moment and 73.6 N pre-load applied to analyse the stress distribution in adjacent segment discs, facet cartilage, and implants. RESULTS: Anatomical measurements confirmed a high similarity between goat and human C5-C6 segments (P > 0.05), validating its use as an experimental model. In biomechanical tests, both CILC and ACDF significantly reduced segmental motion (P < 0.001). Compared with ACDF, CILC demonstrated greater ROM in flexion (3.31° vs. 1.52°, P < 0.05), but superior stability in extension (1.86° vs. 3.86°) and axial rotation (left: 5.89° vs. 8.19°; right: 6.11° vs. 8.89°) (P < 0.05). Finite element analysis confirmed model reliability, demonstrating close alignment between predicted and reported ROM values. CILC generated lower or comparable stress in C3/4 and C4/5 discs compared with ACDF, but higher stress at C5/6. Moreover, CILC resulted in higher facet joint contact forces and implant stress than ACDF, particularly during flexion and extension. CONCLUSION: Although CILC demonstrates biomechanical performance comparable to ACDF with specific advantages in controlling extension and axial rotation without significant advantages, its posterior minimally invasive approach effectively avoids neurovascular risks associated with anterior surgery. The device provides a safer alternative for cervical fusion, particularly in cases with complex anterior anatomy or those requiring revision surgery. However, the observed higher facet and implant stresses underscore the need for careful patient selection, particularly regarding pre-existing facet joint condition and bone quality.