The Anteroposterior Positioning of Viscoelastic Cervical Disc Prosthesis Does Not Alter the Outcomes

Background: While first-generation articulated disc prostheses had an ideal positioning schematically as posterior as possible because of their geometrically determined center of rotation, the dogma may change for viscoelastic implants, whose center of rotation is free. Our hypothesis was to assess whether the anteroposterior positioning (APP) of a viscoelastic implant may influence the clinical or radiological outcomes at follow -up. Methods: Twenty -five patients (mean age 47 years) were evaluated, with an average follow -up of 25.9 months. The primary outcome was the implants' APP on lateral radiographs. APP between 0% and 49% meant anterior centering, 50% perfect centering, and 51% to 100% posterior centering. The cohort was divided into 2 groups: anterior positioning and posterior positioning. Measurements were performed blindly to the functional outcomes. Visual analog scale for neck pain and radicular pain and the Neck Disability Index were assessed. Range of motion was measured at the last follow -up. The C2 to C7 Cobb angle and the spinocranial angle were also measured. Results: The median crude offset from the vertebral endplate center was 0.4 mm (mean: 0.3 mm, Q1: -1.5 mm, Q3: 2 mm; range, -2.9 to 4 mm). The mean overall APP was 49%, 45.2% (95% CI, 43.2%-47.1%) in the anterior group, and 54.1% (95% CI, 51.4%-55.3%) in the posterior group. Fifteen patients were in the group anterior positioning and 10 in the group posterior positioning. The mean spinocranial angle was 79 degrees preoperatively and 74 degrees preoperatively (P = 0.04). Functional outcomes were significantly improved at the last follow -up (P < 10-4). There was no significant correlation between the APP, functional outcomes, and range of motion. Conclusion: The APP of the CP -ESP viscoelastic disc arthroplasty does not significantly influence the clinical or radiological outcomes at follow -up. This study suggests that this type of implant tolerates greater variability in its implantation technique.Level of Evidence: 4.