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. 2025 Jan 14;6(1):82-92.
doi: 10.1302/2633-1462.61.BJO-2024-0118.R1.

Convertible metal-backed glenoid in total shoulder arthroplasty

Riccardo Ranieri  1   2 , Mario Borroni  2 , Giacomo Delle Rose  2 , Marco Conti  2 , Raffaele Garofalo  2   3 , Alessandro Castagna  1   2
Affiliations

Convertible metal-backed glenoid in total shoulder arthroplasty

Riccardo Ranieri et al. Bone Jt Open. .

Abstract

Aims: The aim of this study was to report long-term clinical outcomes of a modern convertible metal-backed glenoid (MBG) in total shoulder arthroplasty (TSA).

Methods: After a minimum of 15 years, a previously studied cohort of 35 patients who received a modern convertible MBG during the period 1996 to 2005 was contacted for clinical and radiological follow-up. At last follow-up, patients were evaluated radiologically and clinically according to the Constant Score, Simple Shoulder Test, and visual analogue scale for pain. Complications and revisions were recorded, and survival analysis was performed.

Results: At the last follow-up, 20 patients were contacted. Of these, 15 patients had experienced at least one complication, and ten underwent revision surgery. The mean time to revision was 13.8 years (7 to 20). Cuff failure was the most common complication. Conversion to reverse shoulder arthroplasty, while maintaining the baseplate, was possible in five cases, with good results. In patients in whom the baseplate was removed, revision was performed significantly later (18.4 vs 11.1 years; p = 0.016). The general revision-free survival was 73% (95% CI 49.5 to 87.3) at 15 years and 38% (95% CI 11.8% to 64.3%) at 20 years, while MBG revision-free survival was 96.0% (95% CI 74.8% to 99.4%) at 15 years and 54% (95% CI 16.2% to 80.8%) at 20 years. Clinical scores showed a negative trend over time, although not statistically significant. Radiologically, polyethylene wear was observed in all cases and was complete in 12 out of 19 cases, and five glenoids were 'at risk' for loosening.

Conclusion: At long-term follow-up, convertible MBG-TSA revealed a high rate of complications and revision surgery, mainly due to soft-tissue failure and polyethylene wear occurring with time. Prompt conversion to RSA maintaining the baseplate provided good results and a low complication rate. Radiological follow-up at about ten years is strictly recommended and, if metal-to-metal contact is observed, conversion to RSA is advisable. These results emphasize the need for continued research into improving TSA outcomes, especially in cases of MBG usage.

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Conflict of interest statement

A. Castagna reports grants or contracts from Lima Corporate (currently Enovis); royalties or licenses from Lima Corporate and Zimmer Biomet; consulting fees from Lima Corporate, NCS Conmed, and Zimmer Biomet; and stock or stock options from Genextra, all of which are unrelated to this work. M. Conti declares royalties or licenses and co-patents with DualSanitaly; and being on the medical board of DyCare, all of which are unrelated. R. Garofalo discloses consulting fees from Arthrex and Medacta, both of which are also unrelated.

Figures

Fig. 1
Fig. 1
Image of the SMR System glenoid (Lima Corporate, Italy).
Fig. 2
Fig. 2
Evaluation of the radiolucent lines. Numbers represent the zones for measurement of the radiolucent lines.
Fig. 3
Fig. 3
Anteroposterior radiograph views showing a 70-year old female patient who had a traumatic rotator cuff rupture after eight years and underwent conversion to reverse shoulder arthroplasty maintaining the original convertible metal-backed glenoid. After 18 years from the first surgery, the implant is still stable.
Fig. 4
Fig. 4
Anteroposterior radiograph views showing a 34-year-old female patient who developed progressive polyethylene eccentric wear with rotator cuff insufficiency noticed at 13 years' follow-up. Conversion to reverse shoulder arthroplasty (RSA) was initially delayed for personal reasons. After 17 years, metal-to-metal contact led to erosion of metal back with severe osteolysis, metallosis with opacification of the periprosthetic soft-tissue (bubble sign and loosening). Conversion to RSA was not possible, so removal of the baseplate and conversion to hemiarthroplasty was performed. po, postooperative.
Fig. 5
Fig. 5
Intraoperative picture of the same case shown in Figure 4. Note the severe eccentric wear of the polyethylene and the metal-backed glenoid, which led to severe metallosis in the surrounding soft-tissue and progressive glenoid loosening.
Fig. 6
Fig. 6
Graph showing survival, considering any revision procedure as the endpoint. The blue line represents the revision-free survival probability, and the shaded area represents the 95% CI.
Fig. 7
Fig. 7
Graph showing survival, considering revision of the metal-backed glenoid as the endpoint. The blue line represents the metal-backed glenoid revision-free survival probability, the shaded area represents the 95% CI.
Fig. 8
Fig. 8
Anteroposterior radiograph views of a 61-year-old female patient with progressive wear of the polyethylene (PE) with reduced thickness between the components. At last follow-up, mild upward migration of the humeral head is observed with complete wear in the superior part of the PE.
See this image and copyright information in PMC

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