Longitudinal migration and inducible displacement of the Mobility Total Ankle System

Abstract

Background and purpose RSA can be used for early detection of unstable implants. We assessed the micromotion of the Mobility Total Ankle System over 2 years, to evaluate the stability of the bone-implant interface using radiostereometric analysis measurements of longitudinal migration and inducible displacement.Patients and methods 23 patients were implanted with the Mobility system. Median age was 62 (28–75) years and median BMI was 28.8 (26.0–34.5). Supine radiostereometric analysis examinations were done from postoperatively to the 2-year follow-up. Standing examinations were taken from the 3-month to the 2-year follow-up. Migrations and displacements were assessed using model-based RSA software (v. 3.2).Results The median maximum total point motion (MTPM) for the implants at 2 years was 1.19 (0.39–1.95) mm for the talar component and 0.90 (0.17–2.28) mm for the spherical tip of the tibial component. The general pattern for all patients was that the slope of the migration curves decreased over time. The main direction of motion for both components was that of subsidence. The median 2-year MTPM inducible displacement for the talar component was 0.49 (0.27–1.15) mm, and it was 0.07 (0.03–0.68) mm for the tibial component tip.Interpretation The implants subside into the bone over time and under load. This corresponds to the direction of primary loading during standing or walking. This statistically significant motion may become a clinically significant finding that would correspond with premature implant failure.

Bone Microarchitecture of the Talus Changes With Aging

“…By contrast, total ankle replacement, which has become more popular as a comparable degree of pain reduction and even better function than common ankle arthrodesis was shown [24,38], may be affected by the changes we observed to the talar body. The most common complication after ankle replacement is aseptic loosening, with 55% with subsidence of the talar component into the talar body being one of the main reasons for failure [19,41,43]. The age-related changes we observed may help to explain this finding.…”

“…Sufficient bone stock is a prerequisite for durability of total ankle replacements [14]; supporting this idea is the fact that one of the most common reasons for implant failure is talar subsidence resulting from periprosthetic osteolysis from polyethylene wear or direct mechanical insufficiency of the underlying bone stock [19,40]. Therefore, given that the mean patient age at total ankle replacement implantation is between 50 and 60 years, knowledge of a potential age effect on bone quality of the talus is of paramount importance [23,42].…”

The Impact of Obesity on the Outcome of Total Ankle Replacement

“…Dunbar et al 15 radiographically assessed migration and displacement of the Mobility total ankle replacement implant in twenty-three patients. They concluded that implants subside into bone over time and under load, corresponding to the direction of primary loading during standing or walking.…”

Risks to the Blood Supply of the Talus with Four Methods of Total Ankle Arthroplasty

“…Similar results were noted by Anderson et al 11 , after a three to eight-year follow-up of fiftyone patients treated with the STAR prosthesis; five of twelve revisions were performed because of talar component problems. Studies of implant systems that we did not include in our study demonstrated a 3% 31 and 10% 32 prevalence of talar osteonecrosis after total ankle arthroplasty, and talar component subsidence has been quantified by radiostereometric analysis 33 . Only recently, if at all, have early outcomes begun to be reported for the three newer implant systems in our study (Salto Talaris, INBONE, and TMTA) 34 .…”