Engineering and clinical analysis of 3D-printed implants for hip arthroplasty

Orthopaedics is on the verge of a revolution with a shift from conventional to three-dimensional (3D) printing manufacture for the mass production of millions of ‘off-the-shelf’ implants, specifically acetabular components for total hip arthroplasty. There is the expectation that 3D-printed implants will last longer and provide better clinical outcomes than their conventional counterparts, but this has not been demonstrated yet. The overarching aim of this thesis was to better understand the engineering and clinical performance of 3D-printed orthopaedic implants to ensure patient safety is maintained as the transition to 3D-printing is more widely adopted. To achieve this, both pristine and retrieved 3D-printed acetabular components were analysed, for the first time, using established and state-of-the-art methods. The reliability of X-ray microcomputed tomography (micro-CT) to characterize both the solid and porous structures of the implants was demonstrated and the scanning parameters for analysis were optimized. Through application of the micro-CT method, a variability was found in the morphometric properties of the porous structures on the backside surface of different designs of pristine 3D-printed acetabular components. A presence of partially molten titanium beads on the backside surfaces was also revealed, suggesting that the post-manufacture processes currently used are inadequate, particularly as the clinical impact of these beads is still unclear. These findings were confirmed by comparing retrieved 3D-printed and conventionally manufactured components. Investigations using micro-CT at higher resolutions showed the presence of cavities (holes) in the material structure, revealing that one of the major pitfalls of 3D-printing, potentially due to suboptimal manufacturing conditions, may affect also medical devices with an unpredictable impact on their clinical performance. Nonetheless, the outcomes of retrieval analysis performed in this project showed that 3D-printed implants may promote enhanced osseointegration compared to conventional components implanted in similar patient cohorts. The results from this thesis provide evidence that helps inform surgeons, implants manufacturers and regulatory agencies on the engineering and clinical properties of 3D-printed orthopaedic implants