Long-term Functional and Radiographic Outcome of a Mobile Bearing Ankle Prosthesis

Abstract

Total ankle arthroplasty is an accepted alternative to arthrodesis of the ankle. However, complication and failure rates remain high. Long-term results of the Scandinavian Total Ankle Replacement (STAR) are limited, with variable complication and failure rates observed. This prospective study presents the long-term survivorship and postoperative complications of the STAR prosthesis. Between May 1999 and June 2008, 134 primary total ankle arthroplasties were performed using the STAR prosthesis in 124 patients. The survivorship, postoperative complications, and reoperations were recorded, with a minimum follow-up period of 7.5 years. Clinical results were assessed using the Foot Function Index and the Kofoed score. The presence of component migration, cysts, and radiolucency surrounding the prosthesis components, heterotopic ossification, and progression of osteoarthritis in adjacent joints were determined. The cumulative survival was 78% after the 10-year follow-up period. An ankle arthrodesis was performed in 20 ankles (14.9%) that failed. Fourteen polyethylene insert fractures occurred (10.4%). Other complications occurred in 29 ankles (21.6%), requiring secondary procedures in 21 ankles (15.7%). Nevertheless, the postoperative clinical results improved significantly. Osteolytic cysts were observed in 61 ankles (59.8%) and the surface area of these cysts increased during follow-up, without any association with the prosthesis alignment or clinical outcome. Heterotopic ossification at the medial malleolus was present in 58 cases (56.8%) and at the posterior tibia in 73 cases (71.6%), with no effect on clinical outcome. Osteoarthritis of the subtalar and talonavicular joint developed in 9 (8.8%) and 11 cases (10.8%), respectively. The long-term clinical outcomes for the STAR were found to be satisfactory. Although these results are consistent with previous studies, the survival and complication rates are disappointing compared to knee and hip arthroplasty. Higher rates of successful outcomes following ankle arthroplasty are important, and these results highlight the need for further research to clarify the origin and significance of the reported complications. Level II, prospective comparative study.