# Polyethylene wear rates in reverse total shoulder arthroplasty: a systematic review of biomechanical studies

## TL;DR

This paper reviews how different materials and implant designs affect polyethylene wear in shoulder replacements, finding that highly cross-linked polyethylene reduces wear compared to conventional materials.

## Contribution

The study is the first systematic review of biomechanical factors affecting polyethylene wear rates in reverse total shoulder arthroplasty.

## Key findings

- Highly cross-linked polyethylene (HXLPE) significantly reduces wear rates compared to conventional polyethylene in reverse total shoulder arthroplasty.
- Larger glenospheres are associated with higher polyethylene wear rates in laboratory settings.

## Abstract

Reverse total shoulder arthroplasty (rTSA) was classically indicated in rotator cuff deficient shoulders with osteoarthritis, although its indications and usage worldwide has grown in recent years. Loosening due to polyethylene wear is a significant concern, especially with increasing use of rTSA in younger patients, and as life expectancy increases. In the context of a lack of clinical data on polyethylene wear rates in rTSA, this study aimed to systematically review the biomechanical literature on factors affecting wear rates in rTSA, with comparison between highly cross-linked polyethylene (HXLPE) and non-HXLPE being of particular interest given the clinical differences shown in total hip arthroplasty.

The PubMed, EMBASE, and Scopus databases were searched for biomechanical studies involving rTSA measuring polyethylene wear rates from April 4, 2024, to inception in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

The search returned 1,211 results, of which 380 were duplicates. Of the remaining 831 records, 773 were excluded based on title and 41 based on abstract, leaving 17 studies for full-text review. Nine biomechanical studies were included. One study showed that the wear rates were significantly lower in HXLPE humeral liners as compared to conventional polyethylene liners (36 mm glenosphere: HXLPE 36.5 ± 10 mm3/million cycles (MC) vs. ultra-high molecular weight polyethylene 83.6 ± 20.6 mm3/MC, P < .001). Wear rates were significantly higher in larger glenospheres (40 mm glenosphere 81.7 ± 23.9 mm3/MC vs. 32 mm glenosphere 68 ± 18.9 mm3/MC, P < .001) than in smaller glenospheres. There were no statistical differences in polyethylene wear rates between implants with vs. without a glenosphere with a central hole, rim damage to the humeral liner, inverse tribological pairing in the liner, and between retentive and nonretentive liners.

HXLPE use in rTSA significantly decreases wear rate as compared to conventional polyethylene in a laboratory-controlled environment. Although this supports the superiority of the biomechanical properties of HXLPE, whether this translates to an improvement in clinical outcomes is undetermined, and limited by the lack of commercially available options despite the ubiquity of HXLPE in prostheses for other joints. Other factors associated with increased wear include larger glenospheres.