Of mousetraps and anatomic glenoid components.

Ralph Waldo Emerson is credited with the saying, "build a better mousetrap and the world will beat a path to your door". 

A similar sentiment may drive the marketing of many different types of glenoid components in anatomic shoulder arthroplasty. Almost all have a polyethylene surface for articulation with the humeral component. The difference lies in the mechanism for fixation to the bone of the glenoid. Below are a few of the many.

One innovation uses porous metal into which bone can grow for fixation. The question is "does this innovation improve outcomes for patients?"  A recently study, A multicenter, randomized controlled trial comparing a second-generation uncemented trabecular metal-backed vs. cemented polyethylene glenoid component in total shoulder arthroplasty: 5-year results compared cemented all polyethylene glenoid components to uncemented trabecular metal glenoid components.

This study found no statistical or clinically relevant advantage of the trabecular metal-backed cementless component over the all polyethylene cemented component. No glenoid implant failures were reported, and complication rates were similar between groups. Metal debris was observed in 11 (23.9%) of the patients receiving trabecular metal components (see circle on x-ray below).

In addition, on the x-ray above it is not clear how much of the original polyethylene remains between the metal backing and the humeral component (red arrows).

The problem of accelerated polyethylene wear with metal backed components was pointed out in Metal-backed glenoid implant with polyethylene insert is not a viable long-term therapeutic option, the authors of which concluded "uncemented MB [metal backed] glenoid resurfacing is not a viable long-term therapeutic option because of accelerated PE [polyethylene]wear leading to early revision surgery". See also

Metal-Backed Glenoid Components Have a Higher Rate of Failure and Fail by Different Modes in Comparison with All-Polyethylene Components: A Systematic Review

The authors of Comparable low revision rates of stemmed and stemless total anatomic shoulder arthroplasties after exclusion of metal backed glenoid components: a collaboration between the Australian and Danish national shoulder arthroplasty registries found that "The adjusted hazard ratio for revision of total shoulder arthroplasties with metal backed glenoid components compared to all-polyethylene glenoid components was 2.54 (95% CI 1.70-3.79, p < 0.001) in the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) and 4.1 (95% CI 1.92-8.58, p<0.001) in the Danish Shoulder Arthroplasty Registry (DSR). The authors concluded "We advocate that metal-backed glenoid components should be used with caution and not on a routine basis."

The Australian Orthopaedic Association National Joint Replacement Registry further studied cumulative percent revision rates by glenoid type including modular metal backed (orange), non-modular metal backed (red), cemented all poly (green), and all poly with a modified central peg (blue). 

An example of an all poly glenoid component with a central peg modified to allow bone ingrowth is shown below.

It is apparent that long term, population-based studies are the key to tracking the outcome of different glenoid component designs. In the meanwhile, we should be prepared for the continued marketing of new glenoid prostheses, such as the 'inset' design shown below.

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link.

Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).