Abstract
Background
Ankle arthroplasty is increasingly used to reduce pain and improve or maintain joint mobility in end-stage ankle arthritis. Both treatments show similar results with regard to functional outcome scores and sport related activities. However, the rates of complications and reoperations were higher after ankle replacement. Particularly for the first implant designs, with more promising results for newer designs.
One of these newer designs is the Mobility Total Ankle System. Short term results in recent literature describe an improvement of functional outcomes; however complication rates vary widely, ranging from 9 to 37% and the 4-year survival rates ranging between 84 and 98 percent. Therefore, the aim of this study was to assess the clinical and radiographic short term results of the Mobility prosthesis.
Methods
Between March 2008 and September 2013, 67 primary total ankle arthroplasties with the Mobility prosthesis were performed, in 64 patients, by one experienced foot and ankle surgeon.
Complications, reoperations, failures and the survival rate were retrospectively examined.
Patient reported outcomes were assessed with the use of the FFI score and visual analogue scale (VAS) for pain. Prosthesis alignment was measured on the first weightbearing radiographs of the ankle according to the procedure described by Rippstein et al.1 (Fig. 1).
Results
The mean follow-up period was 40 months (range 12–78 months). There were two intraoperative and 13 postoperative complications, requiring seven reoperations. The reason for reoperation was painful impingement of the medial and/or lateral gutter (n=4), a deep infection (n=1), subsidence of the talus component (n=1) and a cyst located in the tibiofibular joint (n=1).
Failure occurred in three of the 67 cases, with one early deep infection with a loose tibia component, one case of aseptic loosening and one case of chronic ankle pain without an assignable cause. A two-stage revision, ankle arthrodesis and amputation of the lower leg was performed, respectively. The mean cumulative survival after 61.4 months was 95% (CI 84–98) (Fig. 2).
There was a significant decrease in the median FFI pain and disability score. The pain subscore decreased from 56.4 to 22.2 points and the disability score from 61.1 to 33.3 points. The mean VAS pain was 26.5 for the ankle region.
The tibial components were placed in a mean of 1.5° varus relative to the mechanical axis of the tibia in the frontal plane. Malalignment (>5°) was observed in four cases with a mean of 6.0° varus. In the sagittal plane, a mean posterior slope of 1.6° relative to the mechanical axis of the tibia was measured, with one case of 7.5° of anterior slope. The talar component was centred too far posteriorly in five cases, which was considered as malalignment.
Conclusion
Despite few intraoperative complications and satisfactory clinical and radiological outcome, the incidence of postoperative complications, reoperations and failure indicate the importance of further development and research in the field of ankle arthroplasty.
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