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

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.

Biomechanics of adjacent segments after a multilevel cervical corpectomy using anterior, posterior, and combined anterior-posterior instrumentation techniques: a finite element model study.

Background Context: Adjacent segment degeneration (ASD) after cervical fusion is a clinical concern. Despite previous studies documenting the biomechanical effects of multilevel cervical fusion on segments immediately superior and inferior to the operative segments, the pathogenesis of the initiation of degeneration progression in neighboring segments is still poorly understood.

Purpose: To test the hypothesis that changes in range of motion, disc stresses, and facet loads would be highest at the superior adjacent segment (C3-C4) after anterior C4-C7 corpectomy and fusion and that these changes would be the least in anterior fixation and the greatest in posterior or combined anterior-posterior instrumentation techniques.

Posterior facet load changes in adjacent segments due to moderate and severe degeneration in C5-C6 disc: a poroelastic C3-T1 finite element model study.

Study Design: Biomechanics of normal vertebral segments adjacent to a degenerated segment in the cervical spine.

Objective: To test the hypothesis that posterior facet joints of adjacent segments are loaded more when degeneration occurs in the intermediate disc segment.

Summary Of Background Data: Degeneration progression in adjacent segments is a clinical concern.

Corpectomy versus discectomy for the treatment of multilevel cervical spine pathology: a finite element model analysis.

Background Context: After multilevel fusions, construct failure because of pseudoarthrosis and instrumentation complications is a well-recognized clinical problem. Little is known about the biomechanics governing the cervical spine after different anterior reconstruction techniques, specifically the number of bone grafts and screws used and whether discectomies versus corpectomies have been performed. A few research groups have compared the efficacy of corpectomy and discectomy procedures under common testing conditions; however, no quantitative stress measurements at graft-end plate and bone-screw interfaces have been reported to date.

Progressive disc degeneration at C5-C6 segment affects the mechanics between disc heights and posterior facets above and below the degenerated segment: A flexion-extension investigation using a poroelastic C3-T1 finite element model.

Disc degeneration (DD) is often accompanied by a height reduction of the anterior and posterior discs (AD and PD, respectively), and this affect the way in which articulating posterior facets (PFs) come into contact during physiological motions. Any increase in the contact between overlapping articulating facet surfaces increases PF loading. Development of adjacent segment disease is a significant clinical concern.

Biomechanical effects of anterior, posterior, and combined anterior-posterior instrumentation techniques on the stability of a multilevel cervical corpectomy construct: a finite element model analysis.

Background Context: Multilevel corpectomy, with or without anterior instrumentation, has been associated with both graft and anterior screw-plate complications. The addition of posterior instrumentation after anterior fixation has been shown to increase the overall stiffness of fused segments and decrease the likelihood of instrumentation failure. Little biomechanical information exists for providing guidance in the selection of an appropriate instrumentation technique after a multilevel cervical corpectomy.

Patterns of height changes in anterior and posterior cervical disc regions affects the contact loading at posterior facets during moderate and severe disc degeneration: a poroelastic C5-C6 finite element model study.

Study Design: Biomechanical roles of anterior and posterior portions of the disc (AD and PD, respectively) in governing posterior facets (PF) behavior of a C5-C6 motion segment.

Objective: To understand how height patterns (loss and gain) at AD and PD affects the PF contact loading during moderate and severe grades of cervical disc degeneration (DD).

Summary Of Background Data: PF overloading and degeneration after degenerative disc height loss is a clinical concern.

Simulation of inhomogeneous rather than homogeneous poroelastic tissue material properties within disc annulus and nucleus better predicts cervical spine response: a C3-T1 finite element model analysis under compression and moment loadings.

Study Design: A finite element (FE) modeling of homogeneous and inhomogeneous poroelastic tissue material properties within disc anulus fibrosus (AF) and nucleus pulposus (NP).

Objective: To test the hypothesis that simulation of inhomogeneous poroelastic tissue material properties within AF and NP quadrants, rather than homogeneous properties within regions of AF and NP without quadrants, would better predict the cervical spine biomechanics.

Summary Of Background Data: In order to represent tissue swelling and creep deformation behavior more physiologically in FE models, disc poroelastic tissue material properties should be modeled appropriately.

Relative contributions of strain-dependent permeability and fixed charged density of proteoglycans in predicting cervical disc biomechanics: a poroelastic C5-C6 finite element model study.

Disc swelling pressure (P(swell)) facilitated by fixed charged density (FCD) of proteoglycans (P(fcd)) and strain-dependent permeability (P(strain)) are of critical significance in the physiological functioning of discs. FCD of proteoglycans prevents any excessive matrix deformation by tissue stiffening, whereas strain-dependent permeability limits the rate of stress transfer from fluid to solid skeleton. To date, studies involving the modeling of FCD of proteoglycans and strain-dependent permeability have not been reported for the cervical discs.

Reduction in segmental flexibility because of disc degeneration is accompanied by higher changes in facet loads than changes in disc pressure: a poroelastic C5-C6 finite element investigation.

Background Context: Nerve fiber growth inside the degenerative intervertebral discs and facets is thought to be a source of pain, although there may be several other pathological and clinical reasons for the neck pain. It, however, remains difficult to decipher how much disc and facet joints contribute to overall degenerative segmental responses. Although the biomechanical effects of disc degeneration (DD) on segmental flexibility and posterior facets have been reported in the lumbar spine, a clear understanding of the pathways of degenerative progression is still lacking in the cervical spine.

Reduction in disk and fiber stresses by axial distraction is higher in cervical disk with fibers oriented toward the vertical rather than horizontal plane: a finite element model analysis.

Objective: The purpose of this study was to quantify the biomechanical changes that occur in a compressed cervical disk with the application of axial distraction when the annular fiber orientation angles are varied between the horizontal and vertical planes.

Methods: A 3-dimensional finite element (FE) model of a cervical motion segment was developed. From this model, 3 FE models were developed and validated corresponding to 3 different fiber angles relative to the end plate-disk interface: +/-25 degrees (oriented toward the horizontal plane), +/-45 degrees (midway between the horizontal and vertical planes), and +/-65 degrees (oriented toward the vertical plane).

Motion changes in adjacent segments due to moderate and severe degeneration in C5-C6 disc: a poroelastic C3-T1 finite element model study.

Study Design: Biomechanics of normal vertebral segments adjacent to a degenerated segment in the cervical spine.

Objective: To test the hypothesis of higher motion changes in the segment immediately inferior to a degenerated segment.

Summary Of Background Data: Past research has shown how disc degeneration (DD) affects adjacent segments; however, these studies are conducted only on the lumbar spine or the experimental protocols used are characterized by the presence of degeneration in adjacent segments.

Screw angulation affects bone-screw stresses and bone graft load sharing in anterior cervical corpectomy fusion with a rigid screw-plate construct: a finite element model study.

Background Context: Anterior corpectomy and reconstruction with bone graft and a rigid screw-plate construct is an established procedure for treatment of cervical neural compression. Despite its reliability in relieving symptoms, there is a high rate of construct failure, especially in multilevel cases.

Purpose: There has been no study evaluating the biomechanical effects of screw angulation on construct stability; this study investigates the C4-C7 construct stability and load-sharing properties among varying screw angulations in a rigid plate-screw construct.