Abstract
Introduction
The use of Additive Manufacturing (AM) to 3D print titanium implants is becoming widespread in orthopaedics, particularly in producing cementless porous acetabular components that are either custom-made or off-the-shelf; the primary design rationale for this is enhanced bony fixation by matching the porosity of bone. Analysis of these retrieved components can help us understand their performance; in this study we introduce a non-destructive method of the retrieval analysis of 3D printed implants.
Material and methods
We examined 11 retrieved 3D printed acetabular cups divided into two groups: “custom-made” (n = 4) and “off-the-shelf” (n = 7). A macroscopic visual analysis was initially performed to measure the area of tissue ongrowth. High resolution imaging of each component was captured using a micro-CT scanner and 3D reconstructed models were used to assess clinically relevant morphometric features of the porous structure: porosity, porous structure thickness, pore size and strut thickness. Optical microscopy was also used as a comparison with microCT results. Surface morphology and elemental composition of the implants were investigated with a Scanning Electron Microscope (SEM) coupled with an Energy Dispersive X-ray Spectroscope (EDS). Statistical analysis was performed to evaluate possible differences between the two groups.
Results
We found a spread of tissue coverage, median of 81% (23 – 95), with a trend with time in situ. Custom implants showed a higher spread of porosity, with median value of 74.11% (67.94 – 81.01), due to the presence of differently designed porous areas. Off-the-shelf cups had median porosity of 72.49% (66.67 – 73.07), but there was no significant difference between the two groups (p = 0.164). There was a significant difference in the thickness of the porous structure of the two groups, which were 3.918 mm (3.688 – 4.102) and 1.289 mm (1.235 – 1.364), respectively (p = 0.006). SEM output showed specific morphological features of 3D printed object; EDS analysis suggested that no chemical modifications occurred in vivo, with elemental ratios (Ti/Al = 14; Ti/V = 21; Al/V = 1.51) comparable to previously published results.
Conclusion
This is one of the first retrieval studies of 3D printed orthopaedic implants. We introduced a method for the investigation of these components and micro-CT scanning enabled the non-destructive assessment of the porous structure. This work represents the first step in understanding the performance of 3D printed implants.
