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AAOS Now

Published 10/1/2009
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Mary Ann Porucznik

TAA shows better functional results than fusion

Two-year study supports use of arthroplasty for end-stage ankle arthritis

New prosthetic designs for total ankle arthroplasty (TAA) are providing better function and equivalent pain relief to ankle fusion, according to an award-winning study presented during the American Orthopaedic Foot & Ankle Society’s annual summer meeting.

The study, a 24-month nonrandomized clinical trial, was conducted at 15 equivalent medical institutions offering a broad spectrum of surgical experience. Results after 24 months indicate that the ankles treated with an uncemented, mobile-bearing ankle prosthesis had better function and equivalent pain relief as ankles treated with ankle fusion surgery.

Uncemented, mobile-bearing ankle prostheses are new in the United States, although they have become popular in other countries over the past decade. The study was designed to determine the safety and efficacy of a mobile-bearing prosthesis to treat end-stage ankle arthritis and was approved under an investigational device exemption by the U.S. Food and Drug Administration.

The study’s authors estimate that more than 50,000 new cases of degenerative ankle disease are reported each year. Corresponding author Michael J. Coughlin, MD, notes, “In this prospective comparison between total ankle arthroplasty and ankle arthrodesis regarding function following surgery, the arthroplasty ankle design won hands down.”

An attractive option
The pivotal study design was a noninferiority study with ankle fusion as the control. In a noninferiority study, the primary objective is to demonstrate that a new treatment is equivalent to a standard therapy with regard to a particular result while also having benefits for other clinical end points, thus making the new treatment an attractive option.

The pivotal study involved 158 patients who underwent TAA with the mobile-bearing implant design between September 2000 and December 2001 (TAA group) and 66 patients who underwent ankle fusion between September 2000 and April 2005 (control group).

In addition, a second group of 448 patients underwent TAA between March 2002 and October 2006 (continued access group) after enrollment in the study was closed.

Baseline demographics for each treatment group are shown in Table 1. The most common primary diagnosis in both the pivotal TAA group and the control group was posttraumatic arthritis. Patients in the pivotal TAA group, however, had higher pain and lower function scores than patients in the control group.

Results were reported up to 24 months following surgery. Success was defined by the following four criteria:

  • A 40-point improvement in total Buechel-Pappas ankle score
  • No device failures, revisions, or removals
  • Radiographic success
  • No major complications

At 24 months, researchers had complete data for 96 percent of the pivotal TAA group, 79 percent of the control group, and 66 percent of the continued access group. Complications and the need for follow-up surgery were more common in the pivotal TAA group than in the control group and included intraoperative fractures, intraoperative nerve injury, soft-tissue edema, decreased range of motion, and wound problems.

The need for secondary surgery after TAA was cut by 50 percent, however, in the continued access group compared to the pivotal group; the authors attribute this reduction to improved technique and greater surgeon experience with use of the TAA in the continued access study.

The authors noted that, as surgeons became more experienced, they changed the size of the talar implant, switching from a large component that fit snugly into the mortis to a smaller one. This reduced the incidence of malleolar impingement, pain, and the need for a secondary procedure that would require removal of bone.

At 24-months follow-up, the ankles treated with the mobile-bearing ankle prosthesis had better function and equivalent pain relief than the ankles treated with fusion. The authors note, however, that “longer follow-up is required to better understand the durability and functional longevity” of this TAA design.

A more anatomic design
Dr. Coughlin said, “There is no question that the new design of total ankle replacements is a more anatomic design. It is not cemented and requires less bone resection, and it demonstrates far superior results than the ankle replacements implanted in the 1970s. We are continuing to follow the more than 600 patients involved in the study and will continue to publish results in the future.”

The mobile-bearing ankle design is intended for use in patients with degenerative traumatic and/or rheumatoid arthritis for which conservative measures are no longer successful. Ankle replacement should be reserved for those patients with severe pain and loss of function who no longer get relief from conservative measures.

The study was published in the July 2009 issue of Foot & Ankle International, the official journal of the AOFAS and received the Roger A. Mann Award for best clinical paper presented at the meeting.

Dr. Saltzman, lead author, reports the following disclosure: Wright Medical Technology, Inc.; Pfizer; DJ Orthopaedics; EBI. Dr. Coughlin, presenter, reports the following disclosures: Integra-NewDeal, Tornier-Nexa; SBI.

Coauthors (and reported disclosure) for: “Prospective controlled trial of STAR total ankle replacement versus ankle fusion: Initial results” include Charles L. Saltzman, MD (Tornier, Zimmer, Biomet, DePuy, a Johnson & Johnson Company); Roger A. Mann, MD (Link Orthopaedics);Jeanette E. Ahrens, PhD (disclosure not available); Annunziato Amendola, MD (Arthrex, Inc.; Arthrosurface Inc.); Robert B. Anderson, MD (DJ Orthopaedics; Wright Medical Technology, Inc.); Gregory C. Berlet, MD (Nexa Orthopaedics; Wright Medical Technology, Inc.; Bledsoe Brace; Arthrex, Inc; Pfizer; Biomet; Biomimetic; DJ Orthopaedics; Link Orthopaedics); James W. Brodsky, MD (Integra; DePuy, A Johnson & Johnson Company; Synthes; Smith & Nephew); Loretta B. Chou, MD (no conflicts); Thomas O. Clanton, MD (Arthrex, Inc.); Jonathan T. Deland, MD (Nexa Orthopaedics; Tornier; Zimmer); James K. DeOrio, MD (Merete; Zimmer; Tornier; INBONE; SBI; Integra; Wright Medical Technology, Inc.; Gerson-Lehrman Group; Synthes); Greg A. Horton, MD (Acumed, LLC); Thomas H. Lee, MD (Wright Medical Technology, Inc.; Pfizer; DJ Orthopaedics; EBI); Jeffrey A. Mann, MD (Link Orthopaedics); James A. Nunley II, MD (Link Orthopaedics; SBI; Stryker; Wright Medical Technology, Inc.; Integra Life Sciences; Aircast; Arthrex, Inc; Biomet; Brainlab; Breg; DePuy, A Johnson & Johnson Company; DJ Orthopaedics; EBI; Orthofix, Inc.; Pfizer; Synthes; Tornier; Zimmer); David B. Thordarson, MD (DePuy, A Johnson & Johnson Company; Synthes; OrthoHelix); Arthur K. Walling, MD (AO; DePuy, A Johnson & Johnson Company; DJ Orthopaedics; Encore Medical; Johnson & Johnson; Link Orthopaedics; Merck; Smith & Nephew; Stryker; Zimmer); Keith L. Wapner, MD (Wright Medical Technology, Inc. MemoMetal, Inc.; Small Bone Innovations; EBI, Hangar Orthotics and Prosthetics); and Michael J. Coughlin, MD (Integra-NewDeal, Tornier-Nexa; SBI)

Mary Ann Porucznik is managing editor of AAOS Now. She can be reached at porucznik@aaos.org