Clinical Outcomes and Finite Element Method Results of Anterior Cervical Discectomy and Fusion Using H-Beam Shaped Allospacer: A Comparison with Rim-Shaped Allospacer

Abstract

The main purpose of this study was to evaluate radiologic outcomes and Finite element method (FEM) results of anterior cervical discectomy and fusion (ACDF) using H-beam shaped allospacer, in comparison with rim-shaped allospacer. Methods: From March 2011 to February 2014, 95 patients underwent ACDF using allospacers (H-beam shaped and rim shaped). Sixty-two patients were divided into 2 groups: H-beam shaped allospacer in group A (n=31); rim shaped allospacer in group B (n=31). We retrospectively estimated clinical outcomes, such as, neck and arm pain, radiographic fusion rate and adverse effects. In the FEM study, we compared the performance of 3 different shaped allospacer; i.e., H-beam shaped, H-hole shaped, rim-shaped. We tested the effectiveness of stress distribution from the 3 types of allospacer, using the evaluation criteria of (a) compression; (b) shear; and (c) torsion, under the same load. Results: Neck and arm pain was reduced similarly by 63% to 73% in 2 groups. Fusion rates after 1 year in group A and B were 100% and 98% retrospectively. The complication rates of breakage and displacement in Group B were 16% and 3%. Group A show no adverse effects. From the FEM study, in the cases of the (a), (b), (c), we found that H-beam shaped allospacer resulted in effectiveness stress distribution and diversification regarding compression, shear and torsion compared with rim shaped allospacer. Conclusion: In ACDF using allospacer, H-beam shaped allospacer shows more stable fusion rates with low incidence of complication compared with rim shaped allospacer.

Biomechanical Analysis of Allograft Spacer Failure as a Function of Cortical-Cancellous Ratio in Anterior Cervical Discectomy/Fusion: Allograft Spacer Alone Model

“…It is commonly accepted that greater stress on the endplate and spacers and less contact with the surface of the cancellous portion could lead to an increased risk of subsidence and delayed fusion [10]. In one clinical study, CO-type allospacers, which have a smaller cancellous fusion bed, exhibited more breakage and displacement with disc height loss causing fixation instability, compared with other spacers [13]. In our study, the smaller cortical portion conversely led to an increased subsidence risk and a relatively higher risk of allograft spacer failure despite the wider fusion bed of cancellous bone, especially upon flexion and extension.…”

“…Graft failure with subsidence and breakage leading to non-union are major concerns in ACDF surgery and have been shown to be associated with the use an autologous bone substitute, stand-alone cages, allospacers, reinforcement with anterior plates and screws, and posterior fixation, as well as age and other factors [13,15,[32][33][34][35]. However, no study has analyzed associations of biomechanical stress with cervical spacer design, length, and the ratio of cortical and cancellous portions of the spacers.…”

“…From a biomechanical point of view, the design and ratio of cortico-cancellous composition of allograft spacers have been shown to be associated with graft-related problems, including subsidence and allograft spacer failure, leading to breakage and dislodging in clinical settings [12,13]. The present study used finite element model (FEM) analysis to investigate the associations of different cortico-cancellous ratios of cervical allograft spacers with physical stress on the spacers and with subsidence risk on the endplate and vertebral body in involved spinal segments.…”