Abstract
Introduction Mobile-bearing total ankle arthroplasty has gained more interest in recent years. Clinical results show favourable but varying results, with survival rates between 70% and 90% at 10-year follow-up. Design-specific differences in early migration patterns might explain differences in result and possible modes of failure.
Methods Prospective study of a cementless mobile-bearing total ankle arthroplasty by radiostereometric analysis (RSA). Fifteen total ankle arthroplasties were performed in patients with rheumatoid arthritis. The American Orthopaedic Foot and Ankle Society ankle score and radiostereometric radiographs were evaluated at regular intervals throughout the follow-up period: immediately postoperatively, 6 weeks postoperatively, 3 months, 6 months, and 12 months postoperatively and yearly thereafter.
Results The postoperative clinical results improved. We observed increased migration of the tibial component during the first 3 months, but this stabilized by the 6-months followup. The mean lateral-medial migration was 0.8 mm, distal-proximal migration was 0.9 mm, and posteroanterior migration was −0.5 mm. The latter implicated that the total resultant migration was in anterior and valgus tilting of this tibial component. This resulted in a main mode of migration proximal, anterior and valgus tilting of the tibial component.
Discussion This pilot study showed initial migration of this mobile-bearing ankle prosthesis into upward anterior and valgus tilting. However, migration stabilized at 6 months postoperatively. We think the surgical technique (anterior cortical window for placement) and the method of tibial fixation likely explain this migration.
Correspondence should be addressed to ERASS Office, Schulthess Klinik, Lengghalde 2, CH-8008 ZURICH, Switzerland.
