Static mechanical analysis of the vertebral body after modified anterior cervical discectomy and fusion (partial vertebral osteotomy): a finite element model

BACKGROUND: Modified anterior cervical discectomy and fusion (Mod ACDF) can effectively address ossification of the posterior longitudinal ligament (OPLL), which is difficult to remove directly from the posterior edge of the vertebral body, with considerably lesser damage as compared to anterior cervical corpectomy and fusion (ACCF). We compared the static mechanics of different anterior approaches by using an ideal finite element model. METHODS: A complete finite element model was established and classified into the following three surgical models according to different model cutting operations: ACDF, ACCF, and Mod ACDF. Three different bone volume situations (normal bone mineral density, osteopenia, and osteoporosis) were simulated. After fixing the lower surface of C5 or C6, a load was applied to the upper surface of C4, and the stress distribution and displacement of the upper surface of C5 or C6 were observed and the related values were recorded. RESULTS: The average Von Mises Stress and displacement levels of Mod ACDF were between those of ACDF and ACCF; with the peak Von Mises Stress occurring on the posterior side of the vertebral body (Points 1–4). The change in Von Mises Stress of the vertebral body is not significant during bone loss. However, the degree of displacement of the vertebral body surface and risk of vertebral collapse are increased (100 N: 13.91 vs. 19.47 vs. 21.62 μm; 150 N: 19.60 vs. 29.30 vs. 31.64 μm; 200 N: 28.53 vs. 38.65 vs. 44.83 μm). CONCLUSIONS: The static biomechanical effects caused by Mod ACDF are intermediate between ACDF and ACCF, and the risk of vertebral body collapse is lower than that by ACCF. Therefore, Mod ACDF may be an effective solution when targeting OPLL with poorly positioned posterior vertebral body edges.