Evidence of structural cavities in 3D printed acetabular cups for total hip arthroplasty

Abstract

The use of three-dimensional (3D) printing to manufacture off-the-shelf titanium acetabular cups for hip arthroplasty has increased; however, the impact of this manufacturing technology is yet not fully understood. Although several studies have described the presence of structural cavities in 3D printed parts, there has been no analysis of full postproduction acetabular components. The aim of this study was to investigate the effect of 3D printing on the material structure of acetabular implants, first comparing different designs of 3D printed cups, second comparing 3D printed with conventionally manufactured cups. Two of the 3D printed cups were produced using electron beam melting (EBM), one using laser rapid manufacturing (LRM). The investigation was performed using X-ray microcomputed tomography, imaging both the entire cups and samples sectioned from different regions of each cup. All 3D printed cups showed evidence of structural cavities; these were uniformly distributed in the volume of the samples and exhibited a prevalent spherical shape. The LRMmanufactured cup had significantly higher cavity density (p = .0286), with a median of 21 cavities/mm 3 compared to 3.5 cavities/mm 3 for EBM cups. However, the cavity size was similar, with a median of 20 μm (p = .7385). The conventional cups showed a complete absence of distinguishable cavities. The presence of cavities is a known limitation of the 3D printing technology; however, it is noteworthy that we found them in orthopedic implants used in patients. Although this may impact their mechanical properties, to date, 3D printed cups have not been reported to encounter such failures. K E Y W O R D S3D printing, acetabular cups, additive manufacturing, orthopedic implants, structural cavities

Severe Corrosion of Modular Dual Mobility Acetabular Components Identified During Revision Total Hip Arthroplasty

“…This motion leads to the hallmark findings of chromium-rich black surface deposits and serum cobalt levels significantly higher than chromium levels [23,24]. A recent retrieval analysis of modular cobalt-chromium acetabular inserts revealed evidence of corrosion at the titanium shell-cobalt-chromium modular insert interface [23,25]. This is consistent with our case report, where obvious corrosion was identified on the backside of the acetabular insert and inner surface of the titanium shell.…”

“…Micromotion between 2 dissimilar metals is necessary for MACC to occur. This motion leads to the hallmark findings of chromium-rich black surface deposits and serum cobalt levels significantly higher than chromium levels [23,24]. A recent retrieval analysis of modular cobalt-chromium acetabular inserts revealed evidence of corrosion at the titanium shell-cobalt-chromium modular insert interface [23,25].…”

Off-the-shelf 3D printed titanium cups in primary total hip arthroplasty

“…A visual assessment revealed higher percentages of bony attachment and tissue ingrowth for the 3D printed cups, but the differences comparison with the conventional sockets were not significant[ 13 ]. Hothi et al [ 14 ] compared three 3D printed cups with conventional sockets. Two of the 3D-printed acetabular shells were produced by EBM (Delta TT and Mpact 3D) and one by laser rapid melting (Trident II Tritanium).…”

“…Structural cavities were evident in all the 3D-printed cups and in none of the conventional sockets, with a significantly higher density, but no difference in cavity size, in the laser rapid melting socket. The presence of cavities was attributed to suboptimal manufacturing parameters, gas entrapment, or gaps in the starting powder beads[ 14 ].…”

“…The first open question about 3D-printed cups is about manufacturing. The layer-over-layer production and the highly porous structure may predispose to delamination and fatigue fracture, and the findings about cavities are not reassuring[ 14 ]. Another concern is related to the balling effect of metallic droplets on the molten surfaces, potentially causing cracking and undesired roughness on the inner surface that compromises the locking mechanism and the liner seating, wear, and hardness.…”