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HSS Surgeons Honored for Work on Ankle Mechanics After Joint Replacement

A team of orthopedic surgeons from Hospital for Special Surgery (HSS) in New York City have won the Internal Federation of Foot and Ankle Societies best paper award for their work on how ankle joint replacement affects mobility, which was presented at the 2018 American Orthopaedic Foot and Ankle Society Annual Meeting.

The group, led by Constantine Demetracopoulos, MD, foot and ankle surgeon at HSS, received the honor for their paper, "Influence of Tibial Component Position on Altered Kinematics Following Total Ankle Arthroplasty During Simulated Gait." The article describes experiments to determine how surgical replacement of the joint can affect patient mobility after the procedure.

The surgeon team consisted of Drs. Jonathan Deland, Scott Ellis, and Guilherme Saito, who performed the study in conjunction with Daniel Sturnick in the Biomechanics Department at HSS. The research team utilized a unique robotic gait simulator, which is able to reproduce normal walking gait using human cadavers. The simulator was developed through a generous donation by Herbert Black, owner and CEO of American Iron and Metal Company, under the leadership of Dr. Jonathan Deland, foot and ankle surgeon at HSS.

The findings from the study could help surgeons fine-tune their techniques during ankle replacement to reduce the risk that patients experience complications later on, said Dr. Demetracopoulos. It may also help companies that make artificial joints design implants that are more anatomically friendly and less prone to wear.

"For patients who have ankle arthritis and have an ankle replacement, how we do the replacement and how we position the replacement device is critical to matching the kinematics of normal gait and the success of the procedure," Dr. Demetracopoulos said.

Total ankle arthroscopy (TAA), or ankle replacement surgery, is an option for patients with severe arthritis of the joint. For the procedure, surgeons replace the patient’s diseased ankle with a prosthetic joint composed of metal and plastic. Although the procedure is becoming more common, it is much less so than knee or hip replacement procedures, which number in the hundreds of thousands per year each. As a result, relatively little is known about the best ways to perform the procedure, particularly when it comes to positioning the replacement parts in the bone, or how variations in surgical techniques may affect outcomes.

Ankle replacement surgery is thought to provide patients greater flexibility and motion in the joint than an alternative procedure, ankle fusion. However, despite the significant improvement in pain and mobility following ankle replacement, whether an ankle prosthesis can restore normal walking gait remains unclear. 

For the new study, Dr. Demetracopoulos and his colleagues sought to learn how placement of the ankle implants during TAA affects range of motion. To do so, they implanted artificial ankles (Salto Talaris, Integra LifeSciences) into eight leg sections obtained from cadavers. (The use of cadavers allowed the researchers to more accurately assess ankle motion before and after implant surgery, and also avoided having to expose living patients to excessive radiation from imaging tests.)

To monitor motion, Dr. Demetracopoulos’ group surgically grafted ligaments and tendons from the original joint to sensors. The legs were mounted on a robotic platform with computer software that tracked movement of the ankle in three dimensions: up/down bending of the ankle, side-to-side tilting, and rotation of the bones. "As you bend your ankle up and down, the bone is doing a little bit of all three: From the very top to the very bottom, it’s bending down, it’s tilting and it’s rotating. It doesn’t move like a hinge," Dr. Demetracopoulos explained.

Using the robotic platform to simulate a walking gait, the HSS team found that ankle motion appeared to be restored in two degrees of movement--up/down and side to side tilting. However, rotational motion was significantly greater than before the procedure.  

"We were able to show that the technique of how the replacement is positioned is what drives that rotation," Dr. Demetracopoulos said.

The HSS researchers say the asymmetrical design of the implant used in the study—one of the oldest devices to reach the market that is currently still in use— may play a role in their findings. Newer implant designs may be less prone to such rotational motion, and the group is in the process of trying to evaluate those devices.