Loss of cervical endplate integrity following minimal surface preparation

In vitro biomechanical study.

This biomechanical study was designed to evaluate the loss of endplate integrity with incremental removal of the endplate.

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.

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.

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.

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.