New designs, improved techniques raising TAA’s profile

When total ankle arthroplasty (TAA) was first introduced in the 1970s, implants had good short-term results; long-term data, however, showed severe problems such as osteolysis, component loosening, impingement, infection, and soft-tissue breakdown. As a result, orthopaedists returned to performing ankle arthrodesis, a procedure that often relieves patients’ pain, but reduces ankle mobility and can lead to malalignment, nonunion, and other complications.

Although many orthopaedists still prefer arthrodesis for treatment of severe ankle arthritis, concerns about complications and the emergence of new ankle implant designs have sparked renewed interest in ankle replacement.

Presenters at the 24th annual summer meeting of the American Orthopaedic Foot and Ankle Society—including Brian G. Donley, MD, of the Cleveland Clinic Foundation; Roger A. Mann, MD, of the University of California; and Martin Huber, MD, of Schulthess Clinic, Zurich, Switzerland—contended that recent advancements in TAA, proper patient selection, and careful surgical technique can make the procedure a valid treatment option, and may even allow TAA to reach the same level of success as total hip (THA) and total knee arthroplasty (TKA).

New ankle device designs
Ankle implant designers face several hurdles, including the smaller size of the ankle joint in comparison to hip and knee joints, the ankle joint’s unique articular characteristics, and the amount of force and torques it must withstand.

Current ankle devices are designed to avoid the problems caused by the cemented, two-component, constrained designs of first-generation implants. This latest generation of devices includes both two-component designs (fixed-bearing devices) and three-component designs (mobile-bearing devices) that typically do not require cement.

Fixed-bearing devices have only one articulation between the tibial and talar components, while mobile-bearing implants have a moving, polyethylene bearing that separates the convex talar component from the flat, tibial component. Both types use the ligaments to retain stability and require anatomic balancing following component insertion as well as minimal bone resection (to avoid weakening the bone stock).

“A debate about the benefits of mobile-bearing devices versus fixed-bearing devices is ongoing,” said Dr. Donley. “Clearly, all mobile-bearing prostheses have some benefit because of the automatic repositioning that occurs with the mobile-bearing piece. In addition, that mobile bearing can reduce the effects of implant malpositioning and suboptimal anatomic design.”

In Dr. Donley’s opinion, however, mobile-bearing prostheses introduce several risks, which is why he has been working on a fixed-bearing device design.

“Instability can be a problem with mobile-bearing devices. For that reason, there has to be precise ligament balancing,” he said. “The potential for abrasion is increased with a mobile-bearing prosthesis, and backside wear is a concern. Finally, the potential for catastrophic bearing dislocation has been mentioned in the literature.”

Dr. Huber, who presented the results of a prospective study of a mobile-bearing implant that is currently in clinical trial, pointed out that mobile-bearing devices have had good patient outcomes.

“Patients experience a significant reduction in pain and acceptable ankle motion,” he said, noting that the device had a moderate complication rate, which is common for all TAA, and few severe complications.

Recent studies of TAA with limited follow-up time have shown consistent, good-to-excellent intermediate clinical results. Overall, delays in wound healing—reported at a rate of between 4 percent and 17.4 percent in many studies—are the most common complication from this surgical procedure; deep infections, periprosthetic fractures, and other complications have also been reported.

Researchers have called for 10- and 15-year follow-up studies, including long-term studies by surgeons who were not involved in the design of the prosthesis.

Proper patient selection, surgical technique
Choosing the right candidate for TAA is crucial in the procedure’s success, agreed the panelists.

“Careful patient selection is paramount in achieving good outcomes and implant survivorship,” said Dr. Donley. “Success will be defined before you go into the operating room.”

According to Dr. Mann, the best candidate for TAA is a thin patient with a plantigrade foot and a well-aligned ankle joint secondary to rheumatoid or primary arthrosis.

“The worst candidate,” he said, “is a young patient with severe post-traumatic ankle arthritis and very limited range-of-motion who just wants to be normal again and has unrealistic sports and activity expectations. If a patient says that he can’t wait to have TAA so he can run out on the tennis court, he’s not for the right patient for a total ankle replacement.”

Other contraindications include osteonecrosis of the talus, severe osteoporosis, previous arthrodesis, previous ankle joint osteomyelitis, a severe neuromuscular disorder, neuropathic joint, a non-plantigrade foot, and an excessive coronal plane deformity of approximately 20 degrees.

“I would consider insulin-dependent diabetes a contraindication to TAA, even if the patient doesn’t have neuropathy,” he added.

No matter which implant design the surgeon uses, said Dr. Donley, it’s important to internally rotate the leg prior to surgery.

“Internally rotating the leg brings the mid-axis of the tibia and the fibula parallel to the floor,” he said. “I find that putting the leg in this position makes it easier to approach the ankle and make my cuts straight into the tibia while avoiding the fibula.”

Lessons learned
Years of experience performing TAA have taught Dr. Mann that the procedure “is not forgiving.”

“The surgeon needs to use good, cautious judgment and decision-making processes,” he said. “A surgeon should not let the patient talk him or her into performing TAA if the patient is not a good candidate for this surgery.

“The surgical team really helps,” Dr. Mann continued. “You want a good back-up—especially a plastic surgeon to take care of any skin sloughs that you might encounter.

“In TAA,” he concluded, “the name of the game is patient selection and risk management.”

Jennie McKee is a staff writer for AAOS Now. She can be reached at mckee@aaos.org

Dr. Donley has ties to Tornier, Wright Medical Technology, Medtronic, and Infoslate.

Dr. Mann is a consultant for Small Bone Innovations, Inc. Dr. Huber reports no conflict.

Read JAAOS for more about TAA
The Journal of the AAOS (JAAOS) recently covered various aspects of total ankle arthroplasty. The May 2008 issue includes coverage of an AAOS symposium on “Osteoarthritis of the ankle: The role of arthroplasty” by Loretta B. Chou, MD; Michael T. Coughlin, MD; Sigvard T. Hansen Jr., MD; Andrew Haskell, MD; Gregg Lundeen, MD; Charles L. Saltzman, MD; and Roger A. Mann, MD.

In the September 2008 issue of JAAOS, Andrea Cracchiolo III, MD, and James K. DeOrio, MD, take an in-depth look at the design differences among currently available ankle prostheses, including the four ankle prostheses that have been approved for use by the U.S. Food and Drug Administration. “Design Features of Current Total Ankle Replacements: Implants and Instrumentation” also covers the history of TAA and discusses the limited data available on outcomes of the procedure.

To access the articles, visit www.jaaos.org

References:

1. Chou LB, Coughlin MT, Hansen S, Haskell A, Lundeen G, Saltzman CL, Mann RA. Osteoarthritis of the ankle: the role of arthroplasty. J Am Acad Orthop Surg. 2008;16, 5: 249-259. http://www.jaaos.org/cgi/content/abstract/16/5/249