Comparing 3D Printed Titanium Acetabular Cup Implants

In the recently published ‘Comparative analysis of current 3D printed acetabular titanium implants,’ researchers analyzed innovative medical devices in the form of acetabular cups, meant to improve bone fixation and prevent the need for additional procedures to deal with loosening after total hip arthroplasties.

With over 60,000 3D printed acetabular cups produced for patients today via EBM (and clinically evaluated), the research team completed an independent analysis, comparing three different titanium designs:

• Delta TT (Lima Corporate, Italy) – 3D printed with electron beam melting (EBM), starting from Ti6Al4V powder
• Trident II Tritanium (Stryker, USA) – 3D printed with laser rapid manufacturing (LRM), using titanium-aluminium-vanadium alloy (Ti6Al4V) powder
• Mpact 3D Metal (Medacta, Switzerland) – 3D printed with electron beam melting (EBM), starting from Ti6Al4V powder

Flow chart of the study design

Features on the outer surfaces were measured for the following:

• Porosity
• Pore size
• Strut thickness

Image summarizing the measured parameters related to the lattice structure and cup wall: (a) porosity is the volume of void space in the porous region of interest showed in the zoomed area; pore size is the equivalent diameter of the red shape and strut thickness is indicated by the red arrow; (b) lattice thickness, solid thickness and overall thickness of the cup wall are indicated by the solid, dashed and dotted yellow arrows in the zoomed area of the cross-section of the implant, respectively. The volume rendering and the cross-section are of the Delta TT cup.

The walls of the cups were also measured for:

• Solid thickness
• Lattice thickness
• Overall thickness

Summary of the median (interquartile range) measurements of the morphometric parameters for the three cups

The researchers found differences in comparing the outer surfaces of the cups, related to the 3D printing process, whether EBM or LRM. Partially molten beads were discovered, along with variations in the lattice structures, and pore sizes, cup porosity, and cup walls.

“The analysis of the morphology of the outer surface of the cups from SEM images revealed the presence of partially molten beads on the struts of the porous structures. Smaller beads and higher beads density (beads/ mm2 ) were found on the LRM-manufactured cup (Trident II) compared to the EBM-manufactured cups; this may be due to the smaller titanium powder beads used with the former compared to the latter,” stated the researchers.

These types of beads are not uncommon in 3D printing, but the research team did note how unusual it was to find them in ‘final-build acetabular components,’ as well as the critical need to understand the clinical impact due to the potential for release of titanium from the implants. Despite ‘superior biocompatibility’ of titanium, negative effects are possible, with more study required to find out whether titanium beads and acetabular components could be a concern. Osseointegration is possible, especially in connection with the resulting rough surface.

The ‘highly porous structure’ of the cups demonstrated similarity to human bone but also offers potential for stress shielding because of the stiffness mismatch evident when comparing implants and bone tissue.

“The hexagon-shaped porous structure, Trabecular Titanium (TT), has been previously characterized using cubic and cylindrical samples. The values of porosity, pore size and strut thickness were comparable to our findings. Similarly, the values of porosity and pore size of the Trident II and Mpact cup were comparable to the specifications provided by the manufacturers,” stated the researchers. “The design freedom of 3D printing enables thinner cup walls to be manufactured for a specific cup diameter. This means that a smaller cup can be chosen for specific head size, therefore sparing more bone stock. The three cups showed different dimensions both in thickness of the cup wall and depth of the porous structure.

“This comparison of different designs of 3D printed cups provides manufacturers and regulators, such as the Food and Drug Administration (FDA), the Medicine and Healthcare Products Regulatory Agency (MHRA) and the British Standards Institution (BSI) with evidence that may help to build robust investigation methods for this type of components and to monitor the implants that are already present on the market. Further laboratory studies, analysis of retrieved components and long-term clinical outcomes will help to prevent another metal-onmetal experience from happening.”

3D printed implants continue to be a major source of innovation within the medical realm—as well as a way to offer better treatment for patients, from cervical implants to dental implants to cranial implants, and more.

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Box plots showing the distribution of the measurements of (a) porosity, (b) pore size and (c) strut thickness of the lattice structure of the
three cups. Significant differences (*) were found among the cups

Images showing cross-sections of the three cups (a) Delta TT, (b) Mpact 3D Metal and (c) Trident TT Tritanium. Significant differences were found in the solid, lattice and overall thickness of the cup wall