Backside Wear Analysis of Retrieved Acetabular Liners with a Press-Fit Locking Mechanism in Comparison to Wear Simulation In Vitro

Abstract

Backside wear due to micromotion and poor conformity between the liner and its titanium alloy shell may contribute to the high rates of retroacetabular osteolysis and consequent aseptic loosening. The purpose of our study was to understand the wear process on the backside of polyethylene liners from two acetabular cup systems, whose locking mechanism is based on a press-fit cone in combination with a rough titanium conical inner surface on the fixation area. A direct comparison between in vitro wear simulator tests (equivalent to 3 years of use) and retrieved liners (average 13.1 months in situ) was done in order to evaluate the backside wear characteristics and behavior of these systems. Similar wear scores between in vitro tested and retrieved liners were observed. The results showed that this locking mechanism did not significantly produce wear marks at the backside of the polyethylene liners due to micromotion. In all the analyzed liners, the most common wear modes observed were small scratches at the cranial fixation zone directly below the rough titanium inner surface of the shell. It was concluded that most of the wear marks were produced during the insertion and removal of the liner, rather than during its time in situ.

Articulation and Backside Wear Analysis After Long-Term in Vitro Wear Simulation of Vitamin E Stabilized Polyethylene Acetabular Liners With a Press-Fit Locking Mechanism

“…The observers did not saw a clear change in the type and degree of wear as from the 5 to 10 million cycles analysis, but they did not had the previous results to influence their scoring. Regardless of the scores, the same wear modes and patterns were seen in the current in vitro study and in our previous retrieval study [11]. a previous study from pang et al [33] showed that visual backside damage scoring may not completely correspond with true volumetric wear, as no difference in damage scores were seen between xlpe and cpe liners, but there was three times more penetration in the cpe liners than in the xlpe liners.…”

“…a semi-quantitative method developed by Hood et al [15] and modified for hip implants was used to assess the damage on the backside of the liners. The detailed description of the modified method is given in the previously performed study [11] and will be briefly summarized in the following. On basis of its in situ orientation, the backside section was divided by a superior / inferior line and 7 different sections were determined ( Figure 1).…”

“…a previous retrieval study analyzed the backside wear of acetabular liners with a locking mechanism based on a press-fit cone with a large surface area in combination with a grit blasted rough titanium inner surface along the rim of the acetabular shell [11]. In the study, the backside wear of short-term retrievals made out of conventional standard polyethylene (cpe), highly cross-linked polyethylene (xlpe) and highly crosslinked and vitamin e (0.1%) blended polyethylene was analyzed and compared with their corresponding in vitro tested liners of equivalent life in service, showing similar results among both groups and no significant backside wear due to micro-motion.…”

Comparison of Different Locking Mechanisms in Total Hip Arthroplasty: Relative Motion between Cup and Inlay

“…In addition, Braun et al verified that backside wear particles can occur in clinically established cup systems [15]. Furthermore, Reyna et al was able to detect backside wear caused by micromotion and poor conformity between cup and liner in an in vitro study [25]. As already mentioned, these particles could increase the potential of a resulting inflammatory reaction, which may result in osteolysis.…”

Hip simulator testing of the taper‐trunnion junction and bearing surfaces of contemporary metal‐on‐cross‐linked‐polyethylene hip prostheses

“…These results fit with other studies. Reyna et al compared the wear on the backside of PE (non‐XLPE and XLPE) liners used in a hip simulator test and retrieved liners using a semiquantitative scoring method and reported similar wear scores for both groups . Furthermore, Kurtz et al in 3D finite‐element models showed at least three orders of magnitude less volumetric wear rates from the backside of the liner compared to the volumetric wear rate estimates at the articulating bearing surface …”