Retropharyngeal Reduction Plate for Atlantoaxial Dislocation: A Cadaveric Test and Morphometric Trajectory Analysis

Abstract

Objective: To evaluate the placement feasibility and safety of the newly designed retropharyngeal reduction plate by cadaveric test and to perform morphometric trajectory analysis. Methods:The five cadaveric specimens with intact atlantoaxial joint were enrolled in this study. They were used for simulating the placement process and evaluating the placement feasibility of the retropharyngeal reduction plate. The atlantoaxial dislocation (AAD) of five cadaveric specimens were obtained by proper external force after dissecting ligaments. The retropharyngeal reduction plate was placed on atlantoaxial joint of cadaveric specimens. The X-ray and three-dimensional (3D) spiral CT were used for evaluating the placement safety of retropharyngeal reduction plate. The DICOM data was obtained after 3D spiral CT scanning for the morphometric trajectory analysis. Results:The reduction plates were successfully placed on the atlantoaxial joint of five cadaveric specimens through the retropharyngeal approach, respectively. The X-ray and 3D spiral CT showed the accurate screw implantation and satisfying plate placement. The length of the left/right atlas screw trajectory (L/RAT) was, respectively, 1.73 AE 0.01 cm (LAT) and 1.71 AE 0.02 cm (RAT). The length of odontoid screw trajectory (OST) was 1.38 AE 0.02 cm. The length of the left/right axis screw trajectory (L/RAXT) was, respectively, 1.67 AE 0.02 cm (LAXT) and 1.67 AE 0.01 cm (RAXT). There was no statistical significance between left side and right side in terms of AT and AXT (P > 0.05). The angles of atlas screw trajectory angle (ASTA), axis screw trajectory angle (AXSTA), and odontoid screw trajectory angle (OSTA) were 38.04

The retropharyngeal reduction plate for atlantoaxial dislocation: a finite element analysis

“…Inspired by the TARP, we newly designed the retropharyngeal reduction plate system based on clinical experience. The retropharyngeal reduction plate system can achieve one-stage reduction and fixation after the anterior release ( Li et al, 2022 ). However, the difference in internal fixation strength and stress distribution between the retropharyngeal reduction plate and posterior pedicle screw fixation under different movements is still unknown.…”

“…In this study, we designed the retropharyngeal reduction plate based on a large number of previous clinical experiences to achieve atlantoaxial reduction and fixation in one stage ( Ren et al, 2019 ; Guo et al, 2020 ; Zou et al, 2020 ). The previous cadaveric simulation experiments proved that the retropharyngeal reduction plate could be successfully fixed in front of the atlantoaxial joint through the retropharyngeal approach ( Li et al, 2022 ). Aiming to analyze the fixation strength and stress distribution of the retropharyngeal reduction plate, compared with the posterior pedicle screw fixation, the three-dimensional finite element analysis was conducted.…”

“…The retropharyngeal reduction plate system is characteristic of T-type titanium plates, which includes the screws and different sizes of plates (GB4Z180193509, WEGO ORTHO Co., Ltd.) ( Li et al, 2022 ). The specific plate angle (30°–35°) of horizontal and vertical parts can be conducive to the placement onto the atlantoaxial joint.…”

“…At the same time, we innovatively designed the retropharyngeal reduction plate system inspired by the transoral atlantoaxial reduction plate (TARP). The previous cadaveric simulation experiments showed that the retropharyngeal reduction plate was suitable for placement on the atlantoaxial joint ( Li et al, 2022 ). However, compared with posterior atlantoaxial fixation, there is still a lack of research on the biomechanical properties of the retropharyngeal reduction plate system.…”