328 - In-vitro Characterization of an Anterior Cervical Plate Capable of Ext...

Oral Posters: Innovative Technologies

Presented by: C. Ferry - View Audio/Video Presentation (Members Only)

Author(s):

C. Ferry(1), A. Gandhi(1), S. Farmer(1), J. Inzana(1), J. Wanebo(2), R. Panchal(3)

(1) Zimmer Biomet Spine, Broomfield, CO, United States
(2) Barrow Neurological Institute, Phoenix, AZ, United States
(3) UC Davis, Sacramento, CA, United States

Abstract

Introduction: Adjacent level ossification (ALO) following plated anterior cervical discectomy and fusion (ACDF) remains of primary concern when utilizing the technique. Next-generation plate designs allow for greater oblique screw angulation to help diminish plate profile while still averting the index endplates. However, little consideration has been given in the literature to the implications of increased/extreme oblique angulation on construct rigidity. The objective of this study was to biomechanically assess a novel ACDF plate capable of 30deg cephalad and 30deg caudal screw angulation (60deg total sweep) to determine whether a correlation may exist between screw angulation and segmental rigidity (Figure 1 - left).

Methods: Nineteen (n=19) human cervical spine specimens (C3-T1) were tested. Specimen bone quality was confirmed via DEXA scans and radiographs. Any specimens exhibiting previous surgery or excessive degeneration were excluded. The C3 and T1 vertebral bodies were potted. Each spine was first tested in an intact state. A standard anterior discectomy (C5/C6) was then performed, followed by instrumentation with the MaxAn ACDF System (Zimmer Biomet Spine). Plate size selection and screw angulation was at the discretion of the surgeon in accordance with specimen anatomy. Screw insertion was approximately 1.5mm from the index endplates whenever possible, per device surgical technique guide. Lateral and A/P fluoroscopic images were taken following instrumentation. A 2Nm moment was applied in flexion/extension (FE), lateral bending (LB), and axial rotation (AR) using a six degree-of-freedom kinematics testing frame. Segmental range-of-motion (ROM) was tracked using motion analysis software. Mean ROM relative to intact conditions was reported. Screw angle measurements were made using imagine analysis software. Measurements included 1) angle between cephalad and caudal screws (total sweep) and 2) sum of cephalad and cadual screw angulation relative to affected vertebral endplates (Fig.1 - right). A Pearson correlation for each metric was performed across all principle motion directions.

Results: Screw sweep ranged from 6.4deg to 60.0deg (max), with a median of 38.5deg and a mean of 35.6deg. Summed cephalad/caudal angulation relative to index endplates ranged from 17.9deg to 73.2deg, with a median of 45.3deg and a mean of 44.1deg. Analyses indicated no significant correlations between either angulation metric and ROM reduction in all directions. Screw-to-plate Pearson correlations: FE= -0.12; LB= 0.03; AR= 0.004. Screw-to-endplate Pearson correlations: FE= -0.115; LB= 0.066; AR= 0.046.

Conclusions: Study outcomes indicate that the stability of plated ACDF may not be compromised when using extreme oblique screw angulation. The ability to leverage greater angulation to support a smaller stature plate is clinically advantageous when considering the associated risk of ALO in longer profiles.

Fig 1. MaxAn Plate (L); Measured Angles (R)]

Fig 2. Screw-to-Plate Sweep vs. FE ROM