Morphometric analysis of patient-specific 3D-printed acetabular cups: a comparative study of commercially available implants from 6 manufacturers.BACKGROUND
 3D printed patient-specific titanium acetabular cups are used to treat patients with massive acetabular defects.  These have highly porous surfaces, with the design intent of enhancing bony fixation.  Our aim was to characterise these porous structures in commercially available designs.


 We obtained 12 final-production, patient-specific 3D printed acetabular cups that had been produced by 6 manufacturers.  High resolution micro-CT imaging was used to characterise morphometric features of their porous structures: (1) strut thickness,  Additionally, we computed the surface area of each component to quantify how much titanium may be in contact with patient tissue.  Statistical comparisons were made between the designs.


 We found a variability between designs in relation to the thickness of the struts (0.28 to 0.65 mm), how deep the porous layers are (0.57 to 11.51 mm), the pore size (0.74 to 1.87 mm) and the level of porosity (34 to 85%).  One manufacturer printed structures with different porosities between the body and flange; another manufacturer had two differing porous regions within the body of the cups.  The cups had a median (range) surface area of 756.5 mm2 (348 - 1724).


 CONCLUSIONS
 There is a wide variability between manufacturers in the porous titanium structures they 3D print.  We do not currently know whether there is an optimal porosity and how this variability will impact clinically on the integrity of bony fixation; this will become clearer as post market surveillance data is generated.
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