Biomechanical effects of cervical arthroplasty with U-shaped disc implant on segmental range of motion and loading of surrounding soft tissue

Abstract

Purpose Various design concepts have been adopted in cervical disc prostheses, including sliding articulation and standalone configuration. This study aimed to evaluate the biomechanical effects of the standalone U-shaped configuration on the cervical spine. Methods Based on an intact finite element model of C3-C7, a standalone U-shaped implant (DCI) was installed at C5-C6 and compared with a sliding articulation design (Prodisc-C) and an anterior fusion system. The range of motion (ROM), adjacent intradiscal pressure (IDP) and capsular ligament strain were calculated under different spinal motions. Results Compared to the intact configuration, the ROM at C5-C6 was reduced by 90 % after fusion, but increased by 70 % in the Prodisc-C model, while the maximum percentage change in the DCI model was 30 % decrease. At the adjacent segments, up to 32 % increase in ROM happened after fusion, while up to 34 % decrease occurred in Prodisc-C model and 17 % decrease in DCI model. The IDP increased by 11.6 % after fusion, but decreased by 5.6 and 6.3 % in the DCI and Prodisc-C model, respectively. The capsular ligament strain increased by 147 % in Prodisc-C and by 13 % in the DCI model. The DCI implant exhibited a high stress distribution. Conclusions Spinal fusion resulted in compensatory increase of ROM at the adjacent sites, thereby elevating the IDP. Prodisc-C resulted in hyper-mobility at the operative site that led to an increase of ligament force and strain. The U-shaped implant could maintain the spinal kinematics and impose minimum influence on the adjacent soft tissues, despite the standalone configuration encountering the disadvantages of high stress distribution.

Can an Endplate‐conformed Cervical Cage Provide a Better Biomechanical Environment than a Typical Non‐conformed Cage?

“…The images were then imported into medical image processing software (Mimics 10.1, Materialise to reconstruct the vertebrae geometry volume of C 3 –C 7 (five vertebrae and four intervertebral discs). The finite element model was then created as a reference. Briefly, ABAQUS 6.10 (Simulia, Indianapolis, IN, USA) was used to build and mesh the cervical spine components and implant.…”

Dynamic Cervical Implant versus Anterior Cervical Diskectomy and Fusion: A Prospective Study of Clinical and Radiologic Outcome

“…Mo et al compared the DCI implanted at the segment C5-C6 with the Prodsic-C, ACDF (plate), and the intact spine in a finite element model. 10 ROM in flexion/extension increased by only 7% after DCI implantation but decreased by 30% and 20% in axial rotation and lateral bending, respectively. ACDF decreased ROM by 90% in all motions.…”

“…By contrast, it has been suggested that CDA preserves motion within the total physiologic ROM 22 and, moreover, extends the ROM of the involved segment. 5,10 This may exacerbate the stress on the index facet joints, 5,6,10 particularly in patients with preexisting cervical DDD. 23 The long-term effects of facet joint degeneration after CDA remain to be established, which may have a great impact on the physiologic decrease in ROM with aging.…”

“…Although there have been some conference and industrial reports, [19][20][21]27 only three peer-reviewed reports have been recently published regarding the biomechanical properties 10 and clinical and radiologic results 11,12 of the DCI.…”

“…implantation 8,9 suggested that the contribution to total cervical ROM in flexion/extension and in lateral bending is less than that of the intact cervical spine in ovine specimens. Finite element model analysis 10 revealed better maintenance of spinal kinematic motion than CDA when compared with the intact model. Recently published reports demonstrated the safety and efficiency of DCIs in the treatment of singlesegment cervical DDD.…”