The treatment of ankle arthritis has seen a sea change over the past few decades, with surgeons becoming increasingly confident in offering total ankle arthroplasty to more patients with disability related to arthritis. Surgeons are emboldened by the expanding clinical literature; however, results that are generalizable to the greater foot and ankle community, sufficient numbers, long-term follow-up, and patient-reported outcomes (PROs) are lacking.
The present study by Hsu and Haddad appears to be only the second clinical series to report survivorship and outcomes measures for the INBONE prosthesis, a fixed-bearing implant with intramedullary fixation of the tibial component. In this series of fifty-nine patients, implant survival was 97% at two years and AOFAS (American Orthopaedic Foot & Ankle Society) hindfoot scores and VAS (visual analog scale) pain intensity were significantly improved. However, the 44% complication rate, 24% reoperation rate, and nearly 9% revision rate for talar component subsidence at an average of nearly three years of follow-up are of concern. Validated PRO measures and functional assessments such as those reported in recent studies1-3 would have been of interest.
The only other clinical series to report on the INBONE prosthesis also evaluated fifty-nine patients within a larger cohort of 103 patients; outcomes at two years were assessed in relation to preoperative coronal-plane deformity3. Although subgroup analyses of the INBONE prostheses and the other prosthesis design were not performed, AOFAS scores and the reoperation rate of nearly 20% were similar to those in the present study, but with only one patient undergoing implant revision. The authors reported patient health status, validated measures of ankle function, and measured functional assessments.
These two studies typify the very provisional nature of much of the literature regarding total ankle arthroplasty. The clinical outcomes detailed in these studies, generally with small numbers and short follow-up, likely say as much about patient selection and surgeon skill as they do about the performance of any particular implant system. In contrast, PRO measures evaluating improvement in general health, pain intensity, pain interference, and physical function are most appropriate to assess in the earliest stages of follow-up.
Studies with larger cohorts and longer follow-up do exist to provide surgeons and patients with guidance on implant performance, and two such studies evaluating mobile-bearing total ankle arthroplasty demonstrated 84% to 90% implant survival at ten years4,5. These are reassuring results, but whether they are generalizable to the current group of fixed-bearing systems remains to be seen. Despite the obvious value of those two well-done studies, one included no clinical outcomes measures, and the other included only the AOFAS hindfoot score, the validity of which has been questioned6,7.
A more systematic and coordinated approach that aggregates larger cohorts of patients and that reports standardized, validated PROs will be required to critically evaluate the current and future generations of implants. Recent studies have already validated the National Institutes of Health-funded PROMIS (Patient Reported Outcomes Measurement Information System) physical function index as a measure of ankle osteoarthritis, and the Orthopaedic Foot & Ankle Outcomes Research (OFAR) network, under the auspices of the AOFAS, has already begun aggregating PROs from more than ten centers around the United States8,9. This effort, or meaningful participation by ankle surgeons in the American Joint Replacement Registry (AJRR), is going to be required to give surgeons and patients the information necessary for thoughtful decision-making with regard to ankle replacement.
↵* The author received no payments or services, either directly or indirectly (i.e., via his institution), from a third party in support of any aspect of this work. Neither the author nor his institution has had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, the author has not had any other relationships, or engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
- Copyright © 2015 by The Journal of Bone and Joint Surgery, Incorporated