With its high wear and corrosion resistance, CoCrMo alloy has been widely used for metal-on-metal total hip replacements (THRs). However, the use of the metal-on-metal implants has dropped substantially as a result of several alerts issued by the Medicines and Healthcare products Regulatory Agency (MHRA) due to concern on metal ion release [1]. However, some of the first generation of metal-on-metal THRs have lasted for more than 20 years [2]. It is far from clear why some MoM joints have survived, while other failed. It is known that dynamic changes occur at the metal surface during articulation. For example, a nanocrystalline layer has been reported on the topmost surface of both in vivo and in vitro CoCrMo THRs [3, 4] but it is not known whether this layer is beneficial or detrimental.

The current work focuses on the sub-surface damage evolution of explanted MoM hips, which is compared to in vitro tested CoCrMo hip prostheses. Site-specific TEM cross-section of both in vivo and in vitro CoCrMo samples were prepared by focused ion beam (FIB) in situ lift-out method (Quanta 200 3D with Omniprobe, FEI, the Netherlands). TEM of the FIB specimens was performed on various microscopes. Routine bright field imaging was performed on a Tecnai 20 (FEI, the Netherland) operating at 200 kV, while high resolution transmission electron microscopy (HRTEM) of the nanocrystalline layer and other surface species was undertaken on a Jeol 2010F (Jeol, Japan) operating at 200 kV.

A nanocrystalline layer (which was not present on the starting surfaces) was observed on both explanted in vivo and in vitro tested materials. For the explanted joints, the nanocrystalline layer was thin (a few 100 nm) and the extent did not appear to correlate with the local wear rate. For in vitro samples, the nanocrystalline layer was thicker (up to micron). HRTEM from this layer are shown in Fig. 1 and Fig. 2. The nanocrystallite size was ∼5 nm and appeared to be a mixture of face centred cubic and hexagonal close packed phases. The formation of the nanocrystalline layer and its correlation with wear behaviour are discussed.

Particles generated at the non articulating surface (backside) of modular acetabular components have been implicated in the development of periprosthetic osteolysis after total hip arthroplasty. Several design changes have been introduced in modern uncemented acetabular cups in an attempt to reduce backside wear, including the use of so called “non-modular cups”. We compared the backside wear of retrieved cementless non-modular cups, with modular cups of first and second generation designs.

Nine retrieved non-modular cups (Implex) were match paired for time in situ, patient age and weight, with 9 retrieved Trilogy cups, 9 Harris-Galante 1, and 9 Harris-Galante 2. The average time in situ was 2.5 years (1 to 7). The backside was divided in quadrants and each rated utilizing a score with a value from 0 (absence of wear) to 3 (severe backside wear) for a total ranging from 0 to 12. The score was validated for intra and inter observer reproducibility.

Among 36 quadrants in the HG1 group there were 3 rated 1, 23 rated 2, and 10 rated 3. In the HG2 group, there was 1 quadrant rated 0, 16 rated 1, 14 rated 2, and 5 rated 3. In the Trilogy group, there were 6 quadrants rated 0, 27 rated 1, and 3 rated 2. In the Implex group, there were 15 quadrants rated 0, 21 rated 1. The average total backside wear score and 95%CI were 8.4 (7.6–9.3); 7.3 (5.5–9.1); 3.7 (3.2–4.1); and 2.3 (1.3–3.4) respectively. The HG1 and HG2 groups demonstrated similar backside wear scores (p=0.3). The HG1 and HG2 designs demonstrated significantly more backside wear than the Trilogy and Implex (p< 0.01). The differences between the Trilogy and the Implex were not significant in this cohort.

A comparison of the “in vivo” backside wear of first generation and modern acetabular cups has not been published to date. Despite the limitations imposed by the small sample studied, the presence of multiple screw holes in the HG retrievals, and sub-optimal matching for sex, height, and varied indication for revision, we detected significant reduction in the backside wear of modern modular and non-modular acetabular cups when compared to first generation modular designs.

Backside wear is generated at the non-articulating surfaces of modular acetabular cups. We compared the backside wear of retrieved liners from cementless non-modular and modular cups of first and second generation designs. We match paired for time in situ, patient age and weight, 9 retrieved Harris Galante type 1 liners, 9 Harris Galante type 2, 9 Trilogy, and 9 liners from a modern two-piece preassembled cup (Implex). The average time in situ was 2.5 years (1 to 7). The backside was divided in quadrants and each one examined under a 10x binocular loupe and rated with a score from 0 (absence of wear) to 3 (severe backside wear) for a total ranging from 0 to 12. Among 36 quadrants in the HG1 group there were 3 rated 1, 23 rated 2, and 10 rated 3. In the HG2 group, there was 1 quadrant rated 0, 16 rated 1, 14 rated 2, and 5 rated 3. In the Trilogy group, there were 6 quadrants rated 0, 27 rated 1, and 3 rated 2. In the Implex group, there were 15 quadrants rated 0, 21 rated 1. The average total backside wear score was 8.4; 7.3; 3.7; and 2.3 respectively. The HG cups demonstrated more severe backside wear than the Trilogy and Implex (HG1 vs Trilogy and HG1 vs Implex: p< 0.001; HG2 vs Trilogy and HG2 vs Implex: p< 0.02). There was a tendency towards less backside wear in the Implex cup when compared to the Trilogy (p=0.04). The difference between the HG1 and HG2 was not significant. Despite the limitations imposed by the small sample studied, the presence of multiple screw holes in the Harris-Galante retrievals, and sub-optimal matching for sex, height, and varied indication for revision, we detected significant reduction in the backside wear of modern modular and non-modular acetabular cups when compared to first generation modular designs.

Particles generated at the non articulating surface (backside) of modular acetabular components have been implicated in the development of periprosthetic osteolysis after THA. Several design changes have been introduced in modern acetabular cups in an attempt to reduce backside wear, including the use of “non-modular cups”. We compared the backside wear of retrieved cementless non-modular cups, with modular cups of first and second generation designs. Nine retrieved non-modular cups (Implex) were match-paired for time-in-situ, patient age and weight, with 9 retrieved Trilogy cups, 9 Harris-Galante 1, and 9 Harris-Galante 2. The average time in situ was 2.5 years (1–7). The backside was divided in quadrants and each rated with a value from 0 (absence of wear) to 3 (severe backside wear) for a total ranging from 0 to 12. This new score was validated for intra and inter observer reproducibility. Among 36 quadrants in the HG1 group there were 3 rated 1, 23 rated 2, and 10 rated 3. In the HG2 group, 1 quadrant was rated 0, 16 rated 1, 14 rated 2, and 5 rated 3. In the Trilogy group, 6 quadrants were rated 0, 27 rated 1, and 3 rated 2. In the Implex group, 15 quadrants were rated 0, 21 rated 1. The average backside wear score and 95%CI were 8.4 (7.6–9.3); 7.3 (5.5–9.1); 3.7 (3.2–4.1); and 2.3 (1.3–3.4) respectively. The HG cups demonstrated more severe backside wear than the Trilogy and Implex (p< 0.02). There was a tendency towards less backside wear in the Implex cup when compared to the Trilogy (p=0.04). The difference between the HG1 and HG2 was not significant. We detected significant reduction in the backside wear of modern modular and non-modular acetabular cups when compared to first generation modular designs.