Long-term results with the Agility ankle lend support to ankle arthroplasty

Survivorship at about 90% is nearing that of total hip and knee replacement; other ankle designs have been introduced internationally.

Issue: Issue 5 2003

Outcomes of total ankle arthroplasty with DePuy’s semiconstrained ankle prosthesis now being reported by U.S. foot and ankle surgeons show the procedure has an 11% revision rate at average follow-up of nine years, making it a reasonable alternative to arthrodesis for low-demand ankle arthritis patients.

“This series of nine years should convince anyone,” said Charles L. Saltzman, MD, of Iowa City, U.S.A. He has performed approximately 120 total ankle arthroplasty (TAA) procedures and used DePuy’s Agility prosthesis for 40 of them. It is the only ankle implant approved by the U.S. Food and Drug Administration (FDA).

Approximately 200 patients have received the Agility prosthesis outside the United States. It was introduced in Europe in 2000 and is available in Australia, New Zealand and parts of Asia.

Other TAA designs sold internationally include the Scandinavian Total Ankle Replacement [Waldemar Link; Hamburg, Germany] and the Buechel-Pappas Total Ankle Replacement System [Endotec; Orange, U.S.A.]. They have amassed experience among international investigators of more than 15 and 20 years, respectively, and are currently in U.S. clinical trials.

An uncemented anatomical ankle prosthesis design, the Hintegra prosthesis [Newdeal; Lyon, France], was recently released in Europe, Australia and South Africa. According to developers, it utilizes a mobile bearing and requires minimal bone resection. A revision version is expected to be available this fall.

Alumina ankle prosthesis

This 65-year-old woman's ankle osteoarthritis was severe enough for her to undergo total ankle replacement with the Agility prosthesis.	This radiograph was taken at the patient's eight-year postoperative follow-up, when her ankle was painful but nonproblematic. Computed tomography revealed an osteolytic area in the neck of the talus, which was subsequently grafted successfully.
COURTESY OF FRANK G. ALVINE

Yoshinori Takakura, MD, chairman of the department of orthopaedic surgery at Nara Medical University in Nara, Japan, and co-investigators are using the alumina ceramic TNK ankle implant [Kyocera Corporation; Kyoto, Japan], designed in 1980. It is hydroxyapatite-coated and the tibial component is fixed with a small screw in the posterior cortex.

Of 70 TAA procedures performed in 62 patients from 1991 to 2001 using the TNK prosthesis, three revisions were done due to infection or talar necrosis for a 4% revision rate at average follow-up of 4.7 years, Takakura reported in an e-mail interview with Orthopaedics Today. Results were excellent in 27 patients and good in 26 patients.

“Results with osteoarthritis cases were better than rheumatoid cases. … In the near future, we are redesigning the talar prosthesis fixed by screw. Furthermore, we are trying clinical application of the prosthesis using cultured mesenchymal stem cells from the patient’s bone marrow,” he said.

With improved TAA results, the American Orthopaedic Foot and Ankle Society (AOFAS) recently revised its TAA position statement, moving the procedure into the same category with such operative treatments for symptomatic ankle arthritis as osteotomy and arthrodesis, according to AOFAS President Glenn B. Pfeffer, MD.

“Now it’s clear that TAA is a great benefit to appropriate patients. … Even with our appropriately cautious posture, we feel it’s an important surgical option for a patient with ankle arthritis,” Pfeffer said. Nevertheless, ankle fusion is still a reasonable option for many other patients, he said.

A promising alternative

Saltzman and his co-investigators retrospectively studied clinical and radiographic parameters of 132 consecutive TAA patients with eight- to 17-year follow-up. Frank G. Alvine, MD, of Sioux Falls, U.S.A., operated on the patients from 1984 to 1994. Twenty-two patients received the phase 1 Agility prosthesis and 110 patients received the phase 2 implant available from 1987 through 1997. The phase 2 device had a thicker tibial component and a flat back. Its talar component was made of cobalt chrome instead of titanium.

Frank G. Alvine [photo] Frank G. Alvine, developed the Agility total ankle prosthesis and used it to treat nearly 800 patients with arthritic or deformed ankles.

Investigators used the validated ankle osteoarthritis scale (0=great; 10=bad) to evaluate disability and pain in the patients. They found that patients were modestly worse overall compared to age-matched controls (2.57 vs. 1.40, respectively). Pain subscale scores were even closer: 1.86 for TAA and 1.20 for controls.

More than 90% of the series’ remaining patients, who had 82 implants, were satisfied and would have the procedure again. “They’re satisfied because the amount of pain is less, and their function is somewhat improved compared to the really debilitating pain they likely had prior to undergoing surgery,” Saltzman said.

Agility prosthesis long-term survival rates are approximately 90%, approaching those of total hip and knee replacement. “The phase 2 design was 88% at about five years, and now the phase 3, available since 1997, is 89%. We’re certainly proving that the implant does hold up with time, plus the morbidity is less,” said Alvine, who developed the implant and has performed nearly 800 cases with it.

Low-demand patients

Careful patient selection is critical. In nearly two decades of implanting the Agility prosthesis, Alvine has identified patients who probably should not undergo TAA, including patients with diabetic peripheral neuropathy, extensive talar avascular necrosis and bone loss.

TAA is indicated for moderately to severely painful post-traumatic, degenerative and primary or rheumatoid arthritis of the ankle in a relatively low-demand patient with good skin and soft tissue vascularity and good alignment or easily achievable good alignment of the hindfoot, according to Saltzman.

A stable prosthesis is key. In the Agility model it depends to a great extent on early fusion of the syndesmosis, ideally before six months. According to Alvine, lateral support from a good syndesmotic fusion is important, but some long-term patients have done well without it.

In Saltzman’s review, syndesmotic fusion helped stabilize the tibial component. “Radiographic signs of migration and lysis were associated with delayed or nonunion of the syndesmosis,” investigators reported last year. “Once the tibial component became stabilized it did not move in this series of patients,” Saltzman said.

Lysis followed

Mechanical and expansile lysis were seen on some follow-up radiographs. Approximately half of the patients had evidence of nonproblematic early-onset mechanical lysis. “Three percent of the total group of patients showed progressive expansile lysis at an average of nine years, follow-up,” he said.

In a few patients, talar components subsided and continued to do so for the entire period of the study, often progressing. This occasionally required removal or revision of the component or subtalar fusion, Saltzman said.

The ankle joint’s complexity makes the surgery challenging, Alvine said. “It’s not like a hip or knee. Circulation, skin condition and peripheral neuropathy are very real factors.” Replacing a joint of this nature requires confidence and skill in balancing the foot, he said. “You have to take your time and balance the foot in relationship to the ankle. A malaligned foot just keeps twisting the ankle and then it fails.”

Despite the procedure’s positive aspects, if its more severe complications occur (ie, infection and skin loss), fusion or amputation could be indicated. “If you’re careful with the skin, you can avoid many problems, but some of the problems can be long-term disasters,” Alvine said.

Dr. Alvine has a financial interest in the Agility total ankle prosthesis.