European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society
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We investigated a new metric for assessing the quality of motion of the cervical segments over the arc of extension-to-flexion motion after cervical disc arthroplasty (CDA). We quantified: (1) the amount of motion contributed by individual spinal segments to the total cervical spine motion, termed segmental motion fraction, and its variation throughout the arc of extension-to-flexion motion and (2) how cervical disc arthroplasty using two distinct prosthesis designs may influence the segmental motion contributions. ⋯ The designs of the cervical disc prostheses tested significantly influenced the variation in segmental motion fraction as the spine underwent motion between the endpoints of extension and flexion. While the mean segmental motion contribution to the total cervical motion was not influenced by prosthesis design, the way the motion took place between the extension and flexion endpoints was significantly influenced. The M6-C artificial disc restored physiologic motion quality such that implanted segments continued to function in harmony with other segments of the cervical spine as measured before arthroplasty. Conversely, the Mobi-C prosthesis, while maintaining average motion contributions similar to the pre-implantation values, demonstrated large deviations in motion contribution over the extension-to-flexion arc motion in ten of 16 implanted segments. Such non-physiologic implant kinematics could cause excessive prosthesis wear and motion and stress shielding at adjacent segments. These slides can be retrieved under Electronic Supplementary Material.
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Total disc replacements, comprising all-metal articulations, are compromised by wear and particle production. Metallic wear debris and ions trigger a range of biological responses including inflammation, genotoxicity, cytotoxicity, hypersensitivity and pseudotumour formation, therefore we hypothesise that, due to proximity to the spinal cord, glial cells may be adversely affected. ⋯ The results from this study suggest that microglia influence the effects that metal particles have on astrocytes, that SS ions and particles play a role in the adverse effects observed and that SS is a less toxic biomaterial than CoCr alloy for use in spinal devices. These slides can be retrieved under Electronic Supplementary Material.
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Meta-analyses on the comparison between fusion and prosthesis in the treatment of cervical radiculopathy mainly analyse studies including mixed patient populations: patients with radiculopathy with and without myelopathy. The outcome for patients with myelopathy is different compared to those without. Furthermore, apart from decompression of the spinal cord, restriction of motion is one of the cornerstones of the surgical treatment of spondylotic myelopathy. From this point of view, the results for arthroplasty might be suboptimal for this category of patients. Comparing clinical outcome in patients exclusively suffering from radiculopathy is therefore a more valid method to compare the true clinical effect of the prosthesis to that of fusion surgery. ⋯ ACDF and ACDA are comparably effective in treating cervical radiculopathy due to a herniated disc in radiculopathy patients. Comparing the 8 radiculopathy with the 29 mixed population studies demonstrated that no clinically relevant differences were present in clinical outcome between the two types of patients. These slides can be retrieved under Electronic Supplementary Material.
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Unfortunately, figures 1 and 2 have been incorrectly published in the original publication. The complete correct figures are given below with the captions.