Comparative analysis of conventionally and additively manufactured acetabular shells from a single manufacturer.

Background: The Trident II Tritanium acetabular shell is additively manufactured (3D printed), based on the established Trident 'I' Tritanium shell, produced using conventional methods; this study characterised their differences.

Methods: We obtained 5 Trident I (T1) and 5 Trident II (T2) shells sized 52 mm, 54 mm (n = 3) and 60 mm. We measured their: mass, shell-liner engaging surface roughness, roundness, wall thickness, the depth of the bone-facing porous layer, porosity, and the number, volume and location of structural voids.

Results: The mass varied by up to 13.44 g. The T1 and T2 shells had a median internal roughness of 0.18 μm and 0.43 μm, (p < 0.001) and the median departure from roundness was 6.9 μm and 8.9 μm, (p < 0.001). The 54 mm and 60 mm T2 shell walls were 37% and 29% thinner than their T1 counterparts (p < 0.01). The T2 shells had irregular porous structures, shallower in depth by 11-27% (p < 0.001) than T1 shells, which had repeating mesh units; the overall porosity was comparable (54%). All T2 shells had between 115 and 3415 structural voids, compared with two T1 shells containing 21 and 31 voids. There was no difference in the depth of the porous layer for the 54 mm T2 shells (p = 0.068), whilst T1 shells did show variability (p < 0.01). Both groups showed a variability in surface roughness and roundness (p < 0.01).

Conclusion: This is the first study to compare shells from a single manufacturer, produced using conventional and additive methods. This data will help interpret the performance of the 3D printed Trident II as longer-term clinical data is generated.