Relationship between biomechanical changes at adjacent segments and number of fused bone grafts in multilevel cervical fusions: a finite element investigation

Abstract

Object Biomechanical studies have shown that anterior cervical fusion construct stiffness and arthrodesis rates vary with different reconstruction techniques; however, the behavior of the adjacent segments in the setting of different procedures is poorly understood. This study was designed to investigate the adjacent-segment biomechanics after 3 different anterior cervical decompression and fusion techniques, including 3-level discectomy and fusion, 2-level corpectomy and fusion, and a corpectomy-discectomy hybrid technique. The authors hypothesized that biomechanical changes at the segments immediately superior and inferior to the multilevel fusion would be inversely proportional to the number of fused bone grafts and that these changes would be related to the type of fusion technique. Methods A previously validated 3D finite element model of an intact C3–T1 segment was used. Three C4–7 fusion models were built from this intact model by varying the number of bone grafts used to span the decompression: a 1-graft model (2-level corpectomy), a 2-graft model (C-5 corpectomy and C6–7 discectomy), and a 3-graft model (3-level discectomy). The corpectomy and discectomy models were also previously validated and compared well with the literature findings. Range of motion, disc stresses, and posterior facet loads at the segments superior (C3–4) and inferior (C7–T1) to the fusion construct were assessed. Results Motion, disc stresses, and posterior facet loads generally increased at both of the adjacent segments in relation to the intact model. Greater biomechanical changes were noted in the superior C3–4 segment than in the inferior C7–T1 segment. Increasing the number of bone grafts from 1 to 2 and from 2 to 3 was associated with a lower magnitude of biomechanical changes at the adjacent segments. Conclusions At segments adjacent to the fusion level, biomechanical changes are not limited solely to the discs, but also propagate to the posterior facets. These changes in discs and posterior facets were found to be lower for discectomy than for corpectomy, thereby supporting the current study hypothesis of inverse relationship between the adjacent-segment variations and the number of fused bone grafts. Such changes may go on to influence the likelihood of adjacent-segment degeneration accordingly. Further studies are warranted to identify the causes and true impact of these observed changes.

Adjacent-level biomechanics after single-level anterior cervical interbody fusion with anchored zero-profile spacer versus cage-plate construct: a finite element study

“…As indicated in the present finite element study, ACDF impairs normal cervical biomechanics, alters mechanics at adjacent segments, resulting in higher stress and hypermobility in adjacent segments. Our results are in line with the reported data of the biomechanical studies on the behavior of the adjacent segments in the setting of different operation procedures [49][50][51][52][53]. Both the present and all of the reported results suggested that ASD might be related to iatrogenic biomechanics.…”

Clinical adjacent-segment pathology after central corpectomy for cervical spondylotic myelopathy: incidence and risk factors

“…Our study focused on patients undergoing central corpectomy, which is known to produce increased biomechanical stresses on the adjacent segments, 9 as well as reduced cervical lordosis and segmental height, 19,21 as compared with anterior cervical discectomy and fusion. The range of motion of adjacent segments after central corpectomy changes significantly after surgery, particularly at the inferior adjacent segment.…”

Oblique Lateral Interbody Fusion Combined With Different Internal Fixations in The Treatment of Degenerative Lumbar Spine Disease: A Finite Element Analysis

“…[16, [20][21][22][23]. Ligaments were simulated using springs subject to only pullout force [ The number of nodes and elements of the model is re ected in the following gure [Table 4] [Fig.…”