Loss of Mass and Surface Topography in 3-Dimensional-Printed Solid Titanium Cages Upon Impaction: An In Vitro Model.

Objective: There is increased use of 3-dimensional (3D)-printing for manufacturing of interbody cages to create microscale surface features that promote bone formation. Those features may be vulnerable to abrasion and/or delamination during cage impaction. Our objective was to quantify loss of mass and changes in surface topography of 3D-printed titanium interbody cages due to surgical impaction.

Methods: Eight surfaces of four 3D-printed titanium modular interbody fusion cages were tested. The cages were impacted into the Sawbones model with compression preload of either 200N or 400N using a guided 1-lb (0.45 kg) drop weight. Mass and surface roughness parameters of each endplate were recorded and compared for differences.

Results: Significant weight loss was observed for the superior endplate group and for both 200N and 400N preloads. For pooled data comparison, significant postimpaction decreases were observed for mean roughness, root-mean-squared roughness, mean roughness depth, and total height of roughness profile. No significant differences were observed for profile skewness and kurtosis. There were significant changes in almost all roughness parameters in the anterior region of the cage postimpaction with significant changes in 2 out of 6 parameters in the middle, posterior, and central regions postimpaction.

Conclusion: Three-dimensional-printed titanium interbody fusion cages underwent loss of mass and alteration in surface topography during benchtop testing replicating physiologic conditions. There was an endplate- and region-specific postimpaction change in roughness parameters. The anterior surface experienced the largest change in surface parameters postimpaction. Our results have implications for future cage design and pre-approval testing of 3D-printed implants.