UW Shoulder and Elbow Academy: Reverse total shoulder failure and the issue of polyethylene wear

Backside Polyethylene Wear in Reverse Shoulder Arthroplasty

These authors point out that the particles from polyethylene wear may result in osteolysis and component loosening in reverse shoulder arthroplasty (RSA) - this wear may occur on either the articular side of the polyethylene (PE) or on the backside of the PE liner.

They sought to characterize the damage to the backside and articular surfaces in 21 explanted RSA components.

The mean time between implantation and extraction was 16 months (10 days–88 months). Diagnoses at the time of revision included dislocation (10), infection (4), mechanical failure (3), loosening (2), and unknown (2).

Damage was noted on the articular surfaces of all 21 liners and on the backside surface of 20 liners. The total damage in all the quadrants was higher on the articular surface than on the backside of the component. The articular side exhibited greater scratching, abrasion, and surface deformation than the backside.The inferior anatomical aspect showed the greatest amount of wear.

It is of interest that dislocation was the most common reason for RSA revision in this series, followed by infection. The length of implantation ranged from 0.3 to 88 months.

The photo below shows pitting, typical of backside wear.

The photo below shows major wear (lower left).

Comment: Polyethylene wear in RSA sheds particles of polyethylene into the shoulder throughout the life of the patient. These particles can lead to inflammation, osteolysis and loosening. While this study did not attempt to measure the amount of polyethylene lost from the surface, it is apparent from examples like the one above that this can be substantial. It is possible that the reported deterioration in RSA function observed over time may be related to polyethylene wear and the effect of the released particles.

This issue is addressed in the paper, which was not referenced in the publication above: Analysis of Polyethylene Wear of Reverse Shoulder Components: A Validated Technique and Initial Clinical Results

These authors used a coordinate measurement machine (CMM) and custom computer algorithms to quantify the volumetric wear of polyethylene humeral bearings. This technique was validated using two

never-implanted polyethylene humeral liners with a controlled amount of wear in clinically relevant locations. The technique was determined to be accurate to within 10% of the known value and within 5mm^3 of the gravimetrically determined values.

Following validation, ten retrieved polyethylene humeral liners were analyzed to determine a baseline for future clinical tests. Four of the ten polyethylene humeral liners showed visible and measureable wear volumes ranging from 40 to 90mm^3 total with a maximum wear rate as high as 470mm^3/year in one short duration and significantly damaged humeral liner.

They found dosages of shed polyethylene were well within the osteolytic thresholds that have been suggested, indicating that osteolysis may be a clinical concern in the shoulder.

Further clinical research is needed to determine whether polyethylene wear in vivo can be minimized by using different types of polyethylene, by RSA design and by component positioning.

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Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link)

The smooth and move for irreparable cuff tears (see this link)

The total shoulder arthroplasty (see this link).

The ream and run technique is shown in this link.

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).

Shoulder rehabilitation exercises (see this link).