Biomechanics of dynamic cervical plates may influence clinical results.

Abstract

Authors should be congratulated for their effort in reviewing the usefulness of dynamic plate use in their paper ‘‘Dynamic cervical plate versus static cervical plate in the anterior cervical discectomy and fusion: a systematic review’’ [1], and the contribution in the conclusion of ‘‘similar clinical results with fewer hardware complications for one-level and better similar results for multiple level ACDF’’ is quite clarifying; nevertheless, we would like to point out some issues. The main limitation of the study is the global approach of considering all types of dynamic plates as working identically; no distinction is made among several types of dynamic plates mentioned in the papers (CTEK in Nunleýs [2], Atlantis in DuBois’ [3], and ABC in Pitzens [4]); they are different not only from static plates but also among them, depending on the dynamism based on either rotational (Atlantis) or translational = axial (uni -DOCor bidirectional -ABC-, the latter also has some degree of combined dynamism). This is important because, of the three RCT studies for two-level ACDF, while one study shows no difference in clinical outcome or fusion speed with rotational type (Atlantis, unidirectional) [3], contrarily others favor dynamic for both C-TEK (better clinical outcomes for multilevel ACCF even with higher nonunion rate which—as stated in the paper—may be the consequence of the increased motion and toggling at the graft–bone interface) [2], or ABC (faster fusion, including not only two but also at one level, with fewer hardware complications, which is the reason for progression in the plate design) [4]; on the other hand, even dynamic plates obtain same or superior fusion results with fibular allograft compared to using autologous crest plus static [5]. So the affirmation that ‘‘whether the dynamic plate is advantageous over the static plate in multilevel ACDF is still debated’’ has no longer enough strength, and dynamic (translational) plates should be considered superior not only biomechanically but also in the clinical arena even for one-level ACDF, as the hardware failure rate was higher in ACDF with static plates.