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
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