Commentary & Perspective

Commentary & Perspective on
"The Agility Total Ankle Arthroplasty: Seven to Sixteen-Year Follow-up"
by Stephen I. Knecht, MD, et al.

Commentary & Perspective by
Sigvard T. Hansen, MD*,
Department of Orthopaedics, Harborview Medical Center, Seattle, Washington

(Revised June 10, 2004)

This is an important study for those of us who believe that there is a great need for a functional and reliable ankle replacement. Every operation was performed by the same very experienced surgeon who was also the developer of the device and who fully understands its technical demands. The original 100 patients would have been selected very carefully in all respects, as their results were important to qualify the device for approval by the United States Food and Drug Administration. These arthroplasties were performed with the use of the original device, which was considerably less sophisticated than that available since 1999. Improvements in the newer devices have included an expanded "footprint" (an enlarged posteromedial contact area on the tibial component) and larger talar components with greater talar contact area and a broader upper surface that was better at resisting tilt. A substantial number of patients (about 10%) did not have complete clinical follow-up and another 26% had died, but all had some follow-up.

Dr. Alvine and I have been friends and associates for thirty-five years, and I have been in agreement with his thoughts about development of the Agility implant (DePuy, Warsaw, Indiana) almost from the beginning. My early counsel was to abandon ankle arthroplasty, that ankle fusions were fine when they were done well and that earlier attempts to replace ankles had, in my opinion, failed. He continued working despite my advice, and I began to realize not only that most patients strongly resisted ankle fusions, but that after an average of ten years even my patients with "good" fusions were coming back, disabled by more distal arthrosis. By about 1995, after the United States Food and Drug Administration had approved the Agility, I invited Dr. Alvine to come to Seattle to help us with our first cases. We have now performed more than 600 primary cases and at least 100 revisions. Our approach has been quite different from that of the author, particularly in our use of less selective criteria for patient selection. In addition, we are a teaching institution with many hands on the tools. We have uncovered many problems.

First, the technique is very technically demanding. The alignment of the ankle is not controlled as much by the alignment of the prosthesis itself as by muscle balance, ligament tension, and the stability of the foot, particularly in the subtalar joint. This means that much of the operation involves balancing the musculature of the foot either as part of the arthroplasty or as a separate procedure(s). Frequently required procedures include a gastrocnemius slide, calcaneal osteotomy, posterior tibial tendon augmentation, medial column fusion or, in the case of forefoot-driven hindfoot varus, dorsiflexion osteotomy of the first metatarsal. St. Elmo Newton III, the Seattle pioneer of total ankle arthroplasty in the 1970s, had come to the conclusion that total ankle arthroplasty would be unsuccessful in patients who had even a few degrees of residual varus or valgus¹. We certainly agree that uncorrected angular malalignment is a major contraindication to total ankle replacement, but our approach has been to correct the angular deformity and/or modify the joint position to accommodate the deformity.

I will summarize what we have learned from seeing hundreds of patients with severe end-stage arthrosis of the ankle. First, Dr. Alvine's technique of fusing the syndesmosis to stabilize the tibial component certainly seems valid in that we have had virtually no problems with long-term fixation of the tibial component when it was properly sized and the syndesmosis had fused. But the talar component, as alluded to in the article, is another story. In many cases, failure of fixation is almost impossible to detect without direct inspection and is associated with persisting pain, swelling, and overgrowth of bone. In our experience, this may occur in 20% to 25% of patients with the earlier talus models. The talar component also can subside late for various reasons, including weight gain or sudden impact, and occasionally the talus itself may break. Use of the newer talus models, removal of a minimal amount of talus, and possibly the addition of osteoconductive or osteoinductive agents to the fixation surface may improve the outcomes of the talar component. The newer designs along with conservative resection of the talus have certainly reduced the rate of subsidence and fracture.

Younger, active patients have a higher prevalence of progressive lysis. In some patients with ten-year follow-up, we have noted the massive "expansile" lysis that was described in this paper. The lytic areas are filled with a caseous brownish material that contains refractive particles, assumed to be the result of polyethylene wear.

Our most important finding has been that most failed ankles can be quite easily and very successfully revised instead of fused, and our rate of revision to fusion is nearly 10:1. Revisions usually involve just the talar component and polyethylene, but may necessitate removal of a solidly bonded tibial component. This requires special instruments, such as thin disposable chisels, to avoid removing much bone. Usually, reinserting the next larger size prosthesis after débridement and management of any other associated problems, such as malalignment, produces a good result. We are starting to use methylmethacrylate more often in older patients, usually only on the talar side. Also, a new custom-stemmed talar replacement that crosses the subtalar joint is proving very helpful after substantial destruction of talar bone and/or the subtalar joint, but I would caution that insertion of this component is a complex technical challenge.

Finally, an attractive approach in younger patients is to perform primary fusion with plans to convert it to an Agility prosthesis at a later time. Surprisingly, taking down a fusion and getting good motion and function is quite reliable when the fusion was performed conservatively and when all required structures, including the malleoli and ligaments, have been retained.

Even though we have encountered multiple problems by offering this procedure to patients with suboptimal indications, I believe ankle arthroplasty is close to being very reliable. Although we have seen occasional disastrous failures, rare infections, and an amputation rate of approximately 1%, most of these complications have occurred in patients with complex problems. Encouragingly, many patients find that total ankle arthroplasty is almost miraculous in restoring them to the level of near-normal activity, much as arthroplasty of the hip and knee has done for many years.

*The author did not receive grants or outside funding in support of their research or preparation of this manuscript. The author received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (occasional consulting fees from DePuy). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

1. Newton SE 3rd. Total ankle arthroplasty. Clinical study of fifty cases. J Bone Joint Surg Am. 1982;64:104-11.

Copyright © 2004 by the The Journal of Bone and Joint Surgery, Inc.