STUDY DESIGN: In vitro biomechanical study.
OBJECTIVES: This biomechanical study was designed to evaluate the loss of endplate integrity with incremental removal of the endplate.
SUMMARY OF BACKGROUND DATA: The position of the anterior cervical motion preserving prosthesis is very important. Unlike interbody bone graft, where a certain amount of settling is tolerable and potentially advantageous with respect to the fusion rate, a settled total disc replacement will not function properly and may dislodge. Partial or aggressive endplate removal may be a factor resulting in subsidence of an interbody device. This study was designed to precisely examine the change of endplate strength following precise burring of the surface.
METHODS: Eight human cadaver cervical spines (C3-C7) were dissected and 6 locations on the endplates from each vertebra were biomechanically tested using an indentation test protocol. Pairs of locations were randomly assigned to be burred to the depth of 0 mm (intact), 1 mm, or 2 mm before the testing using a flat 3-mm end mill. Strength of the endplate was statistically analyzed to examine the effect of the depth of the burr and any regional variations.
RESULTS: Significant differences (P < 0.0001) in endplate strength was noted between the intact endplate (106 +/- 86 N) and burred endplates (1 mm depth, 59 +/- 49 N; 2 mm depth, 51 +/- 46 N). No significant differences existed between the burr depths of 1 and 2 mm (P = 0.21). The posterior endplate was significantly stronger than the anterior endplate irrespective of depth of burr.
CONCLUSION: There is a significant loss of endplate integrity when 1 mm of endplate (44% loss) or 2 mm of endplate (52% loss) is removed. Although the implant interface plays an important role in the magnitude of the subsidence of a device, this study in general shows that the endplate is important in terms of maximizing the strength of a construct.
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