Comparison of Survivorship and Failure Modes Between Anatomic and Reverse Total Shoulder Arthroplasty Across Multiple Government Joint Registries for a Single Platform Shoulder System.

INTRODUCTION

We analyzed two different government joint registries for survivorship associated with one platform shoulder system and compared reasons for revision and trends in usage of anatomic total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (rTSA) over a period of more than 10 years to elucidate reasons for any changes in market trends.

METHODS

A review of the United Kingdom (UK) and Aus- tralian national joint registries was performed for a single platform shoulder prosthesis (Equinoxe; Exactech, Inc, Gainesville, Florida, USA) from 2011 to 2022 to investigate changes in annual usage rates of primary aTSA and primary rTSA relative to differences in survivorship and reasons for revision for each prosthesis type.

RESULTS

Between June 2011 and July 2022, 633 primary aTSA and 4,048 primary rTSA were performed in Australia, and 1,371 primary aTSA and 3,659 primary rTSA were per- formed in the UK with the same platform shoulder prosthesis. Over this period of use, rTSA utilization increased annually at a greater rate than aTSA for this platform shoulder pros- thesis. Specifically in Australia, primary aTSA use increased annually by an average of 38.3% while primary rTSA use increased annually by an average of 148.9%. Similarly, in the UK, primary aTSA use increased annually by an aver- age of 14.0%, while primary rTSA use increased annually by an average of 32.4%. Additionally, the overall incidence of aTSA and rTSA revisions was low; 99 of 2,004 primary aTSA (4.9%) patients and 216 of 7,707 primary rTSA (2.8%) patients with this specific platform shoulder prosthesis were revised. The average 8-year cumulative revision rate for primary aTSA patients was higher than that for primary rTSA patients; 7.7% of aTSA patients were revised at 8 years (0.96% revised/year), but only 4.4% of primary rTSA patients were revised at 8 years (0.55% revised/year). No difference in hazard ratio for all-cause revisions was ob- served for the Equinoxe aTSA or rTSA as compared to all other aTSA systems in either registry. Some differences in the reasons for revision were observed between aTSA and rTSA, where most importantly, rTSA patients experienced only one case of revision due to rotator cuff tears or sub- scapularis failure as compared to the 34 cases of rotator cuff tears or subscapularis failure with aTSA, which accounted for more than one-third of all aTSA revisions. Furthermore, soft-tissue related failure modes were the most common reasons for aTSA failure and were responsible for 56.5% (34.3% rotator cuff tears or subscapularis failure and 22.2% instability or dislocation) of all aTSA revisions; in contrast, soft-tissue related failure modes were responsible for only 26.9% (26.4% instability or dislocation and 0.5% rotator cuff failure) of all rTSA revisions.

CONCLUSIONS

This multi-country registry analysis utiliz- ing independent and unbiased data of 2,004 aTSA and 7,707 rTSA of the same platform shoulder prosthesis demonstrated high aTSA and rTSA survivorship in two different markets over a period of more than 10 years of clinical use. A dra- matic increase in rTSA utilization was observed in each country. Reverse total shoulder arthroplasty patients were demonstrated to have a lower revision rate at 8 years and were not as susceptible to the most common failure mode associated with aTSA: rotator cuff tears or subscapularis failure. The reduction in soft-tissue related failure modes with rTSA may explain why so many more patients are now being treated with rTSA in each market.