A meta-analysis of the outcomes of semi-constrained, unconstrained, and constrained cervical artificial disc designs

Cervical disc arthroplasty (CDA) is a surgical treatment indicated for symptomatic pathologies of the cervical spine. Cervical disc designs fall under one of the three categories: semi-constrained, unconstrained, or constrained. This meta-analysis aims to provide an overview of differences in postoperative outcomes and functional scores among the three types of cervical discs.

A literature search was conducted on PubMed and Embase through June 2025. Comparison studies that included at least two of the disc categories and reported outcomes of interest were included in this study. Review Manager 5.4. was utilized for statistical analyses, and a P-value ≤0.05 was considered statistically significant.

Fifteen studies were included, with a total of 1341 patients. Comparing semi-constrained to unconstrained, a significant difference in operative time was found in favor of semi-constrained, while the incidence of heterotopic ossification (HO) was found in favor of unconstrained. Comparing semi-constrained to constrained, a significant difference in incidence of HO was found in favor of semi-constrained. Lastly, comparing unconstrained to constrained, significant differences were found in the changes of Visual Analog Score-Neck, Neck Disability Index, 12- Item Short Form Survey Physical Component Score, and Functional Spinal Unit (FSU) total range of motion in favor of unconstrained, while the change of FSU angle was found in favor of constrained.

Unconstrained cervical discs seem to provide better functional scores compared to constrained discs, with an advantage in the rate of HO compared to semi-constrained discs. There does not seem to be many significant differences between semi-constrained compared to unconstrained and constrained cervical discs in terms of functional scores and complications. Future studies should be carried out to identify the most effective disc design.

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