Comparison of radiographic parameters after anterior cervical discectomy and fusion with semiconstrained translational versus rotational plate systems

Objective: A plate is commonly applied after anterior cervical discectomy and fusion (ACDF); particularly in cases of multilevel fusion. Recent comparative studies have focused on constrained versus semiconstrained plates, however little data is available to assess differences between semiconstrained plates. Patients and Methods: A retrospective review of 60 consecutive adult patients undergoing a 1, 2 or 3 level ACDF with a lordotic allograft for treatment of symptomatic cervical spondylosis was conducted at a single center. The cohort was separated into two groups depending on the cervical plating system used. Patients in the first group had a semiconstrained translational plate and those in the second group had a semiconstrained rotational plate. Plain neutral radiographs were assessed preoperatively, immediately after surgery and at most recent follow-up. The measured radiographic parameters focused on sagittal alignment, adjacent segment pathology, fusion rate and implant failure. Results: There were 30 patients in each group. There were no significant differences in demographic characteristics or distribution of levels fused between groups. All patients had at least 6 months of follow-up and mean follow-up was 14.8 +/- 6.2 months in the translational plate group and 13.1 +/- 4.8 months in the rotational plate group (p = 0.227). Significant improvement in sagittal segmental alignment was noted in both groups following surgery. The translational plate group improved from 1.0 +/- 7.5 degrees to 4.8 +/- 7.6 degrees (p = 0.03) and the rotational group improved from 2.7 +/- 9.1 degrees to 8.4 +/- 7.8 degrees (p = 0.001). This significant sagittal correction was maintained through follow-up for those in the rotational plate group; 5.5 +/- 9.1 degrees (p = 0.002). However, a partial loss of segmental lordosis was observed in the translational plate group leading to a failure to maintain significance of the lordotic correction; 1.7 +/- 8.3 degrees (p = 0.280) over the follow-up period. Segmental fusion rates were not significantly different between groups. However, there was a higher rate of screw breakage within the rotational plate group (4 instances versus 0 instances in the translational plate group). Conclusion: This comparative cohort series suggests that performing an ACDF with a lordotic allograft using either semiconstrained translational or rotational plate system allows for correction and maintenance of cervical alignment, however the rotational plate appears more effective at maintaining segmental lordotic correction. Further prospective controlled study will be needed to determine if this may come at the expense of greater rates of instrumentation failure in the rotational plate group.