Biomechanics following skip-level cervical disc arthroplasty versus skip-level cervical discectomy and fusion: a finite element-based study

Abstract

BackgroundModerately increased motion at the intermediate segment (IS) after skip-level fusion may accelerate disc degeneration. However, limited biomechanical data are available that examine the effects on the IS following cervical disc arthroplasty (CDA). The purpose of this study is to investigate the biomechanical changes in the IS of the cervical spine after skip-level fusion or skip-level arthroplasty.MethodsA finite element model of a healthy cervical spine (C2-C7) was constructed. Two surgical models were developed: (1) skip-level fusion at C3/4 and C5/6 and (2) skip-level arthroplasty at C3/4 and C5/6. A 75-N follower load and 1.0-N·m moments were applied to the top of the C2 vertebra to produce flexion, extension, lateral bending and axial rotation in the intact model. The end-points in each direction corresponding to the intact model were applied to the surgical models under displacement-control protocols.ResultsThe ranges of motion (ROMs) of the fusion model were markedly decreased at the operated levels, while the corresponding ROMs of the arthroplasty model were similar to those of the intact spine in all directions. In the fusion model, the ROMs of the IS (C4/5) were markedly increased in all directions. The ROMs in the arthroplasty model were similar to those in the intact spine, and the ROMs of untreated segments were evenly increased. In the fusion model, the intradiscal pressure and facet contact force at were C4/5 remarkably increased and unevenly distributed among the unfused segments. In the arthroplasty model, the IS did not experience additive stress.ConclusionThe IS does not experience additive ROM or stress in the intervertebral disc or facet joints after skip-level arthroplasty, which has fewer biomechanical effects on the IS than does skip-level fusion. This study provides a biomechanical rationale for arthroplasty in treating patients with skip-level cervical degenerative disc disease.

Biomechanical comparison of noncontiguous cervical disc arthroplasty and noncontiguous cervical discectomy and fusion in the treatment of noncontinuous cervical degenerative disc disease: a finite element analysis

“…The implants and the cervical vertebra models were assembled in the software mentioned above. Considering the C3/4 and C5/6 were the most frequently discussed levels in previous studies, these two levels were chosen as the implanted levels in our study [1,8,12]. In the arthroplasty group, we inserted Prodisc-C at C3/4 and C5/6 after removing the anterior longitudinal ligament (ALL), the posterior longitudinal ligament (PLL), and intervertebral discs at the corresponding locations.…”

“…ROMs of our FEMs in flexion-extension, lateral bending, and axial rotation were compared with the data from previous studies [8,[18][19][20]. The ROMs of the intact FEMs at C2/3, C3/4, C4/5, C5/6, and C6/7 were 4.11°± 0.75°, 5.22°± 1.10°, 5.74°± 1.08°, 5.70°± 1.11°, and 4.39°± 0.94°, respectively, in flexion; 3.24°± 0.79°, 4.23°± 1.03°, 4.65°± 1.01°, and 4.04°± 1.03°, respectively, in extension; 5.15°± 0.85°, 4.84°± 1.15°, 4.73°± 1.29°, 3.42°± 0.77°, and 2.63°± 0.58°, respectively, in lateral bending; and 2.04°± 0.83°, 2.97°± 0.79°, 3.73°± 0.67°, 3.14°± 0.62°, and 2.20°± 0.93°, respectively, axial rotation (Fig.…”

“…It has been reported that the preservation of IS could ameliorate postoperative outcomes [7]. However, most of the studies preserved the IS with noncontinuous ACDF, which would bring more additive stress from the fused levels and then cause hypermobility on IS; all of these would cause the acceleration of ASD [8].…”

“…Previous studies reported that multilevel CDA could achieve better clinical outcomes compared with one-level CDA, even though the surgical techniques of multilevel CDA were more difficult and the inclusion criteria were stricter [10,11]. Furthermore, Wu et al [8] reported that noncontinuous CDA could reduce the biomechanical impact on the IS compared with noncontinuous fusion. However, they only built a standard set of models for analysis, lacking a statistical comparison of multiple patient models.…”

“…However, they only built a standard set of models for analysis, lacking a statistical comparison of multiple patient models. In addition, most studies have discussed the effectiveness of Prestige LP in noncontinuous CDA, but the use of Prodisc-C in this kind of operation has not been fully discussed [1,8,12,13]. Therefore, the aim of this research is to analyze the biomechanical characteristics of noncontinuous ACDF and noncontinuous CDA based on multiple patient models, comparing the differences between these two kinds of treatment methods, and to verify the effectiveness of Prodisc-C in noncontinuous CDA.…”