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Study: Weight-Bearing CT Scan and 3D Biometrics Can Enhance Assessment and Presurgical Planning for Total Ankle Replacement

The use of a weight-bearing CT scan providing three-dimensional biometric measurements can enhance the preoperative assessment and surgical planning for total ankle replacement, according to a study at Hospital for Special Surgery (HSS) in New York City. 

The research paper, titled, "The Use of Three-Dimensional (3D) Biometric Measurements to Predict Additional Alignment Procedures in Total Ankle Replacement" was presented today at the American Academy of Orthopaedic Surgeons Annual Meeting in Las Vegas. 

"The foot and ankle is a highly complex anatomical and biomechanical structure, and preoperative evaluation of deformities in patients undergoing total ankle replacement is challenging," said Constantine A. Detracopoulos, MD, an orthopedicsurgeon specializing in foot and ankle surgery at Hospital for Special Surgery and senior investigator. "The final decision to perform associated corrective alignment procedures and soft tissue balancing is made during surgery following insertion of the ankle replacement components."

Conventional x-rays are limited in their ability to characterize foot and ankle deformities due to their two-dimensional nature, according to Cesar de Cesar Netto, MD, who presented the study. The complexity of the foot and ankle and the importance of weight-bearing in diagnosis have prompted the use of standing CT scans to provide a more complete 3D picture of alignment and deformities, he noted. 

At HSS, the weight-bearing CT is standard of care. "This is a growing research field in foot and ankle orthopedics. The goal is to determine how this technology can improve our patient outcomes," Dr. Demetracopoulos noted. 

The researchers launched a pilot study to determine if the information provided by the standing CT could improve surgical planning prior to ankle replacement. Software designed for the scanner was used to calculate a new biometric measurement called the Foot and Ankle Offset (FAO). Surgeons could use this information to assess the alignment of the foot underneath the ankle and predict which additional surgeries, such as tendon transfers or osteotomies, might be needed during total ankle replacement. 

"Proper alignment is critical to the success of ankle replacement surgery and the longevity of the implant," said Dr. Demetracopoulos, who noted that the study, which included 12 patients, was the first of its kind. "The key in ankle replacement is to optimize not only the alignment of the ankle, but the alignment of the foot underneath."

The researchers found that an increased FAO significantly predicted the number of additional alignment procedures needed during ankle replacement. "We believe that the use of biometrics and measurements provided by the CT scan can enhance the preoperative assessment and surgical planning of total ankle replacement," Dr. Demetracopoulos said. "Future research will determine if it leads to improved outcomes, as well."