Total ankle survivorship rates are low: Improvements may be underway

Investigator reports significant advances in surgical instrumentation.

NEW ORLEANS — Although total ankle replacement survivorship rates are considerably lower compared to those of hip and knee replacements, a leading foot and ankle surgeon said that the success rates for total ankles will improve.

Based on a literature review, Charles L. Saltzman, MD, president of the American Orthopaedic Foot and Ankle Society (AOFAS), said that the 5-year survivorship of total ankle replacements (TAR) is approximately 80%.

“What do we expect from primary total knee and primary total hips at 5 years? Well if you are a primary total knee or hip surgeon and you have a 78% survivorship at 5 years, you are out of business,” Saltzman said at the AOFAS Specialty Day Meeting, here, during the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons.

Saltzman presented a brief history of TARs and commented on the progress made in areas such as bone-implant fixation, bone resection and surgical equipment. He also provided his opinion regarding the future of TAR.

Refined instrumentation

Charles L. Saltzman

Significant improvements have been made to TAR surgical instrumentation with the help of engineers and industry involvement, Saltzman said.

“Surgical equipment has gotten better, and that is an important point I think, because it reduces variation, and it improves the likelihood of a good outcome,” he said.

Saltzman said that future improvements could include navigation and robotic-controlled surgery.

The big picture

“I think in 2010 and the future, we may see porous metals coming in [TAR],” Saltzman said, and noted the potential of porous metals to solve current problems with fixation and load transfer.

Saltzman said that the question of optimal bone resection is still up for debate, but that there is a trend toward respecting the natural architecture of bone.

“In 2010, we have better fixation, more focused joint surface replacement, improving approaches to bone resection, better prosthetic articular geometry and more sophisticated surgical equipment,” he said. “I believe the future is bright for total ankles.” — by Thomas M. Springer

Reference:

• Saltzman CL. The big picture: Total ankle replacement in 2010. Presented at the American Orthopaedic Foot and Ankle Society Specialty Day Meeting, held during the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons. March 13. New Orleans.

• Charles L. Saltzman, MD, can be reached at the Department of Orthopedics, University of Utah, 590 Wakara Way, Salt Lake City. UT 84108; 801-587-5404; e-mail: charles.saltzman@hsc.utah.edu.

There is no doubt that total ankle replacement has much improved in the last years. While I do concur with Saltzman that survivorship rates are still lower compared to those of hip and knee replacements, there is evidence that survivorship at 5 years is probably significantly higher than the indicated 80%.

Most recent reports on current ankle designs have shown survivorship of 92% to 98%. Nevertheless, the underlying problems of the osteoarthritic ankle are more critical than those of the osteoarthritic hip or knee. First, post-traumatic osteoarthritis accounts for approximately 80% of cases. The surrounding soft tissues are thus often of bad quality, and bony geometry and alignment may have changed. Second, the patients are mostly younger, by approximately 10 years on average; thus they are more active.

I do also concur with Saltzman that refined instrumentation for more accurate resection cuts and improved surfaces for increased bony ingrowth may be important reasons for ongoing improvements. However, besides those reasons, it has to be emphasized that there are other specific factors determining the outcome of total ankle replacement. In particular, accurate balancing of the replaced ankle is probably the key for long-term success, as this protects the replaced ankle against asymmetric wear and overload of surrounding soft tissues. In addition, a well-balanced ankle may evidence less intrinsic stress and shear forces on the implant-bony surface. Better fixation techniques and improved bony ingrowth may help to increase the primary stability of implants, but they probably do not guarantee for long-term success so long as the ankle joint is not properly balanced.

Based on the survival of my own patients series over more than 15 years, I am convinced that the result of a replaced ankle highly depends the extent to which the surgeon was able to balance the ankle joint complex, and how accurately she or he was able to restore the joint surfaces. Thus, more efforts are necessary to thoroughly understand the ongoing changes in and around the osteoarthritic ankle and its adjacent joints.

Last but not least, the surfaces and biomechanics of some current ankles should be critically questioned with regard to improvements to get closer to the normal ankle.

– Beat Hintermann, MD
Associated Professor University of Basel, Chairman Orthopaedic Clinic, Kantonsspital, Liestal, Switzerland

Reference:

• Hintermann B. Total ankle replacement — where are we in 2009? Presented at the 26th Annual Meeting of the Southern Orthopaedic Association. July 15-18, 2009. Amelia Island, Florida.

I fully agree with Saltzman about the lower rate of survival of ankle prostheses if compared with those of hip and knee. Nonetheless, “materials and methods” for ankle prosthesis are not yet so advanced as those of hip and knee. Of course, everything can be improved (surgical techniques, surgical instrumentations and surgeon expertise), but I think the main issue is prosthesis design. In fact, all the available models actually do not respect anatomy or ligament isometry, which is fundamental to obtain the correct joint biomechanics. With such characteristics, it would be possible to reduce stresses, wear and consequent osteolysis.

Most available prostheses, either with two or three components, are not anatomical — as already said — and that is an essential requirement, together with the compatibility with the natural isometry of ligaments. It follows that if the shape of a component is changed, the curvature of the talus must be changed too.

I can confirm that, on the one hand, improvements of surgical techniques, including computer assistance, surgical equipment and surgeon expertise, are important to the development of better ankle prostheses; on the other hand, no significant progress can be reached without a good anatomical prosthetic design with special care to the maintenance of the natural ligament isometry. I believe that enhancement of these two features will increase the survival rate of ankle prostheses.

– Sandro Giannini, MD
Full Professor of Orthopaedics and Traumatology, Director of the School of Orthopaedics of Bologna University, Director of 2nd Department of Orthopaedic and Trauma Surgery at Istituto Ortopedico Rizzoli, Bologna, Italy