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.

Objective
Our study aimed to compare the posterior interposition technique against the posterolateral transosseous technique in the same cadaver specimens.
Methods
Computer and cadaver models of 2 fixation techniques were developed. The computer model was constructed to analyze bone volume removed during implant placement and the bony surface area available for fusion. The cadaver model included quasi-static multidirectional bending flexibility and dynamic fatigue loading. Relative motions between the sacrum and ilium were measured intact, after joint destabilization, after fixation with direct-posterior and posterolateral techniques, and after 18,500 cycles of fatigue loading. Relative positions between each implant and the sacrum and ilium were measured after fixation and fatigue loading to ascertain the quality of the bone-implant interface. The 2 techniques were randomized to the left and right sacroiliac joints of the same cadavers.
Results
The posterior interposition technique removed less bone volume and facilitated a larger surface area available for bony fusion. Posterior interposition significantly reduced the nutation/counternutation motion of the sacroiliac joint (42% ± 8%) and reduced it more than the posterolateral transosseous technique (14% ± 4%). Upon fatigue loading, the posterior interposition implant maintained the bone-implant interface across all specimens, while the posterolateral transosseous implant migrated or subsided in 20%–50% of specimens.
Conclusion
Posterior interposition fixation of the sacroiliac joint reduces joint motion. The amount of fixation from the posterior technique is superior and more durable than the amount of fixation achieved by the posterolateral technique.