Clinical comparison of fixed bearing versus mobile bearing total ankle replacement

S Bitar, J Davenport, M Karski, J Ring, R Smith, T Clough

Aims: We compared the clinical outcomes of a fixed bearing (Infinity) and a mobile bearing (Zenith) ankle replacement in a demographically similar group of patients, from a single, non designer centre.

Methods: Between December 2010 and May 2016, 118 consecutive mobile bearing prostheses (Zenith) and between September 2017 and November 2019, 118 consecutive fixed bearing (Infinity) prostheses were implanted in a total cohort of 230 patients. Demographic, clinical, and patient reported outcome measures (PROMs) data were collected. The end point of the study was failure of the implant requiring revision of one or more of the components. Kaplan Meier survival tables were generated.

Results: Demographics were similar for both groups (age, pre-operative arthritic diagnosis and co-morbidities). 32 patients (36 ankles) died during follow-up, but none required revision. Of the surviving 198 patients (200 ankles; 93 Zenith, 107 Infinity), mean follow-up was 9.1 years (6.0 - 13.1 years) for Zenith and 5.0 years for Infinity (3.6 €“ 6.8 years). A total of 11 implants (9.3%) failed for Zenith and 1 implant (0.8%) failed for Infinity, requiring revision. Average time to failure for Zenith was 3.4 years (0.4 - 10.5 years) and the time to failure for Infinity was 4.1 years. Implant survival at five years, using revision as an endpoint, was 91.3% for Zenith and 98.7% for Infinity. There was a mean improvement in Manchester-Oxford Foot and Ankle Questionnaire (MOXFQ) from 85.0 to 32.8 for Zenith and 79.3 to 26.4 for Infinity, and visual analogue scale (VAS) scores from 7.0 to 3.2 for Zenith and 6.9 to 2.7 for Infinity. The commonest reason for revision was aseptic loosening for both implants.

Conclusion: Our results show a significantly better survivorship for the fixed bearing over the mobile bearing prosthesis. Whilst the fixed bearing prosthesis had better PROMS scores, this was not significant.