Saturday, September 11, 2021

Trabecular metal-backed glenoid component - does this innovation add value for the patient with shoulder arthritis?

Two-year results of a multi-centre, randomized controlled trial comparing a second-generation uncemented trabecular metal-backed versus cemented polyethylene glenoid component in total shoulder arthroplasty 

These authors report two-year postoperative findings from a randomized controlled trial (RCT) comparing  disease-specific quality of life (QOL), clinical, patient-reported, and radiological outcomes in patients undergoing a total shoulder arthroplasty (TSA) with a Zimmer/Biomet cemented polyethylene glenoid (POLY) component to those receiving a second-generation Zimmer/Biomet uncemented trabecular metal (TM) glenoid shown below

A total of 93 patients were randomized (46 TM; 47 POLY). 

No significant or clinically important differences were found with patient-reported outcomes at 24-month follow-up.  Grade 1 metal debris was observed in three (6.5%) patients with TM glenoids.

There was no radiological evidence of glenoid component migration in either group.  Radiolucent lines around the glenoid implant were observed in eight patients (17%) in the POLY group but the severity was minor in most patients (6 = 1 mm; 1 = 2 mm; 1 = 6 mm). In the TM group, ‘possible’ lucency around the glenoid was reported in one patient.

With respect to the humeral stem, subsidence was observed in four (8.5%) patients in the POLY group and seven (15.2%) in the TM group.  Radiolucent lines  were observed in three (6.4%) and five (10.9%) patients in the POLY and TM groups, respectively.

Comment: This is a well-done randomized controlled trial. The two year data do not demonstrate an advantage of the metal-backed component over an all polyethylene component. The authors noted metal debris in three patients, but this did not appear to be associated with inferior outcomes. 

In their discussion they pointed out that an issue with this metal backed component is that should revision, for example to a reverse total shoulder because of cuff failure, is difficult because of the large glenoid bone defect left after removal of the metal-backed ingrowth glenoid component.

While metal backed glenoid components tend to have low rates of radiolucent lines and loosening, they have been found to have higher revision rates in large population studies such as that of the Australian Registry

Metal back glenoid components have also been found to have failure modes that differ from those of all-polyethylene components, see: Metal-Backed Glenoid Components Have a Higher Rate of Failure and Fail by Different Modes in Comparison with All-Polyethylene Components: A Systematic Review

By contrast, long-term revision rates for all-polyethylene glenoid components using modern materials and techniques appear to be low, as shown by these data from the Australian Registry

At present, evidence is lacking to support the view that metal-backed glenoids offer increased value to the patient with glenohumeral arthritis in comparison to an all-polyethylene component. 

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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).