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INFINITY® total ankle system
Abstract
The INFINITY® Total Ankle System (Wright Medical Technology, Inc., Memphis, TN) (WMT) is a modern, fourth-generation, fixed-bearing, two-component total ankle replacement. Specific parameters of deformity correction achievable with this prosthesis, like any other, are based on the experience of the surgeon more so than by the engineered characteristics of the implant itself. However, as with other resurfacing-type prostheses, this prosthesis is ideal for patients with limited deformity and relatively younger patients where maintenance of bone stock is critical, especially on the talar side of the joint. Optimal maintenance of talar bone stock is a principle that is accepted by total ankle replacement surgeons and allows maximal surgical options when revision surgery is required.
... The operative technique utilized standard instrumentation as previously described 12 until computed tomography (CT) scan-derived, patientspecific instrumentation (PSI; Prophecy, Wright Medical Technology, Memphis, TN) became available in 2014. Thereafter, PSI was used for all cases, apart from 2 cases in which insurance approval for PSI could not be obtained. ...
Aims:
This study presents the first report of clinical and radiographic outcomes of the Infinity Total Ankle System (Wright Medical, Memphis, TN) with minimum 2-year follow-up.
Patients and methods:
The first 67 consecutive patients who underwent primary total ankle arthroplasty (TAA) with the Infinity system at 2 North American sites between August 2013 and May 2015 were reviewed in a prospective, observational study. Demographic, radiographic, and functional outcome data were collected preoperatively, at 6 to 12 months postoperatively, and annually thereafter.
Results:
The overall implant survival rate was 97% (65 of 67 implants) at a mean follow-up of 35.4 months (27 to 47 months). Two cases underwent talar component revision for aseptic loosening. Six of the 67 cases (9%) required a nonrevision reoperation. Mean Foot Function Index and Ankle Osteoarthritis Scale scores at latest follow-up improved from preoperative by 21.6 ( P < .0001) and 34.0 ( P < .0001), respectively. No radiographic loosening of any talar or tibial components was identified in the 65 nonrevised cases.
Conclusion:
Early clinical and radiographic outcomes with the Infinity TAA are promising and compare favorably to those reported for both fixed- and mobile-bearing third-generation TAA designs, even when used in cases with deformity and increased case complexity.
Levels of evidence:
Level IV.
Background and objective:
Loosening and wear are still the main problems for the failure of total ankle arthroplasty, which are closely related to the micromotion at the bone-implant interface and the contact stress and joint motions at the articular surfaces. Implant design is a key factor to influence the ankle force, motions, contact stress, and bone-implant interface micromotion. The purpose of this study is to evaluate the differences in these parameters of INBONE II, INFINITY, and a new anatomic ankle implant under the physiological walking gait of three patients.
Methods:
This was achieved by using an in-silico simulation framework combining patient-specific musculoskeletal multibody dynamics and finite element analysis. Each implant was implanted into the musculoskeletal multibody dynamics model, respectively, which was driven by the gait data to calculate ankle forces and motions. These were then used as the boundary conditions for the finite element model, and the contact stress and the bone-implant interface micromotions were calculated.
Results:
The total ankle contact forces were not significantly affected by articular surface geometries of ankle implants. The range of motion of the ankle joint implanted with INFINITY was a little larger than that with INBONE II. The anatomic ankle implant design produced a greater range of motion than INBONE II, especially the internal-external rotation. The fixation design of INFINITY achieved lower bone-implant interface micromotion compared with INBONE II. The anatomic ankle implant design produced smaller contact stress with no evident edge contact and a smaller tibia-implant interface micromotion. In addition, significant differences in the magnitudes and tendencies of total ankle contact forces and motions among different patients were found.
Conclusions:
The articular surface geometry of ankle implants not only affected the ankle motions and contact stress distribution but also affected the bone-implant interface micromotions. The anatomic ankle implant had good performance in recovering ankle joint motion, equalizing contact stress, and reducing bone-implant interface micromotion. INFINITY's fixation design could achieve smaller bone-implant interface micromotion than INBONE II.
Background
The number of ankle and revision ankle replacements performed is increasing. There is limited research into functional outcomes, especially in revision ankle replacements. The primary aim of this cohort study was to determine the functional improvements following primary and revision ankle replacements and compare which gave the greatest improvement in functional scores.
Methods
A single-center prospective cohort study was undertaken between 2015 and 2018. All patients were followed up for a minimum of 2 years. Patients undertook a preoperative and 2-year Manchester Oxford Foot Questionnaire (MoxFQ) score. The Mann Whitney test was undertaken.
Results
A total of 33 primary and 23 revision ankle replacements were performed between 2015 and 2018. The mean age was 69.3 years for primary replacements and 64.7 years for revision replacements. All primary replacements were the Infinity ankle replacement. Revision replacements were either the Inbone II or Invision. The indication for revision was 9 aseptic loosening, 6 infections, 5 cysts, and 3 malposition. Seventeen were performed as a single stage and 6 as a 2-stage revision. The overall MoxFQ improved by a mean of 48.8 for primaries and 20.2 for revisions ( P = .024). The walking/standing domain improved by 57.5 for primaries and 22.5 for revisions ( P = .016), the pain score improved by 43.0 and 32.3 ( P = .009), and the social interaction improved by 40.0 and 11.7 ( P = .128).
Conclusion
Both primary and revision ankle replacements result in improved functional scores. In this relatively small cohort with the implants used, primary ankle replacements though have a significantly greater improvement in functional scores compared to revision ankle replacements.
Level of Evidence
Level II, prospective cohort study.
Heterotopic ossification after total ankle arthroplasty (TAA) is a known sequela and has been reported to contribute to reduced range of motion and poor functional outcomes. However, conflicting results have been reported in the literature. The present study documents the incidence of heterotopic ossification for a novel fourth-generation fixed-bearing 2-component prosthesis and reports a systematic review of the literature. We reviewed the incidence and functional outcome of consecutively enrolled patients who underwent primary Infinity TAA between 2013 and 2015 in a prospective observational study. Preoperative and postoperative radiographic and functional outcome data were collected. A systematic review was also conducted investigating all published studies between 1998 and 2018 reporting the incidence of heterotopic ossification after TAA. The incidence of heterotopic ossification was 70.5% in the 61 patients who underwent primary TAA in the case series. There was no association between heterotopic ossification and American Orthopaedic Foot and Ankle Society (AOFAS) score, foot function index (FFI), visual analogue scale (VAS), and ankle osteoarthritis scale (AOS). Sixteen studies on 1339 TAA implants were included. The overall incidence of heterotopic ossification after TAA was 66.0% at average 3.6 years (range 22.2% to 100%). Four studies (299 ankles) did not address functional outcomes. Eleven studies (960 ankles) reported no association between heterotopic ossification and functional outcomes. One study (80 ankles) reported a statistically significant difference in range of motion (7°) and AOFAS score (7 points). In conclusion, although the incidence of heterotopic ossification after TAA is considerable, there is insufficient literature to suggest that heterotopic ossification after TAA impacts range of motion or functional outcome.
Total ankle arthroplasty has been in development for more than 40 years. Although early designs were experimental with high failure rates, current implants are significantly improved, showing promising functional results and clinical outcomes. Total ankle replacement designs are split into mobile-bearing and fixed-bearing designs. When deciding whether to perform ankle arthroplasty, many factors need to be considered to determine if the patient is suitable and which implant is the best fit for patient and surgeon. Many prostheses are available in the United States today and the purpose of this article is to outline options for foot and ankle surgeons.
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