Developments in Total Ankle Replacement

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For impediments in ankle function, arthrodesis has long been favored over arthroplasty. Restoring full function through prosthetic replacement has historically been complicated by the difficulty in dislocating the ankle for access during surgical intervention as well as the many other nearby foot joints and complex biomechanics that characterize the region. Until recently, fusion has seen much wider practice with its union rate of roughly 90%. However, over the past decade there has been a significant uptick in total ankle arthroplasty (TAA) worldwide, and today both procedures when successful are known to provide significant and fairly long-lasting pain relief.

While durable, arthrodesis of the ankle permanently eliminates all native ankle mortise and can therefore disturb gait and stress nearby joints of the foot, according to a 2013 study in the Rhode Island Medical Journal. For these reasons, tertiary care orthopedic foot and ankle specialists are pursuing innovations in TAA that are likely to promote its wider adoption. Christopher DiGiovanni, MD, chief of the Foot and Ankle Center and director of the Foot and Ankle Fellowship Program at Massachusetts General Hospital, has been at the forefront of the study, design and implementation of newer generation of ankle replacement devices and protocols. While ankle replacement technology has not yet caught up to innovations in other load bearing and major joints, which enjoy a survivorship of 90% to 95% over 15 to 20 years, recent studies indicate that newer generation ankle replacement techniques have demonstrated an improved postoperative survivorship of 80% to 95% over five to 10 years. While these intermediate results should still be considered early by joint replacement standards, they represent potentially promising advancements in prosthetic design, instrumentation and longevity of these implants.

Iterative Improvements in Prosthetic Design

First- and second-generation ankle prosthetic designs presented constraint issues and limited function, which caused them to be either too restrictive or too unstable. This often led to implant loosening, dislocation, chronic pain and occasional catastrophic failure. Many also required removal of a significant amount of bone in the distal tibia and talus before implant insertion, which often caused premature collapse in soft bone, progressive bone loss and difficult revision situations.

Today's newer third- and fourth-generation models have corrected many of these shortcomings, benefiting from recent advances in implant technique and design, as well as a far-improved understanding of ankle biomechanics and the impact that concomitant ipsilateral foot pathology can have on ankle implant predictability, function and durability. The results, says Dr. DiGiovanni, are a more reproducible gait cycle, more physiologic implant mortise, greater postsurgical activity and, most importantly, fewer significant complications or need for any revision surgery.

Among these models is one designed and patented by Dr. DiGiovanni, the first FDA-approved third-generation design to enable insertion through either a medial or lateral approach, a strategy that has proved influential with later designs. New models are now put in as press-fit designs that have greater geometrical biocompatibility. They come with a greater degree of freedom that prevents undue stress transfer without being unstable, require less bony resection for insertion so that revision is easier, and offer options for significant modularity to provide for a better fit. Many are coated with tiny beads that allow for the surrounding bone to grow into the prosthesis, forming a lasting bond that allows for bony remodeling over time.

Instrumentation, Patient Expectations and Further Study

The instrumentation used during the surgery is another area upon which Dr. DiGiovanni and other surgeons have worked to improve. Precise instrumentation for making the bony cuts and ensuring anatomic alignment during surgery is critical, says Dr. DiGiovanni. These implants are smaller than those of hip, knee and shoulder replacement, yet by virtue of location are mandated to do more work. Slight inaccuracies in this area can have large consequences on implant durability, including even subtle instability, stiffness or any type of underlying foot malalignment that might go unaddressed, according to a 2004 study by Dr. DiGiovanni and colleagues in Operative Techniques in Orthopaedics.

Given the growing patient demand for TAA, clinician-scientists now appreciate a parallel need for setting proper functional expectations pre-surgery. Dr. DiGiovanni and the team at Mass General conducted a cross-sectional survey of fellowship-trained orthopedic foot and ankle specialists across the United States, published in Foot and Ankle Surgery in 2015, which was designed to analyze the athletic and routine activity of daily living restrictions physicians place on patients following ankle replacement surgery. Physicians rated approximately 50 sport and other activity choices, from which the researchers derived a set of consensus recommendations that include guidance on low-impact aerobic exercises, sports and other activities for these patients.

The rapid development of TAA as well as its markedly increased demand over the past 10 years also call for the study of long-term effects. In conjunction with the Biomechanics Laboratory in the Department of Orthopaedics at Mass General, Dr. DiGiovanni is currently applying for several biomechanics grants to study the kinematic effects of ankle arthritis and TAA on surrounding joint function and, more importantly, the effects that foot malalignments, such as flatfoot or high-arch deformity, or motion abnormalities like instability and stiffness, might have on TAA kinematics.

In 2017, Dr. DiGiovanni and colleagues also wrote two references: a commentary and a perspective piece on the differences between today’s ankle fusion and ankle replacement options in the nation’s leading peer review journals. The commentary appeared in The Joint of Bone & Joint Surgery, while the perspective appeared in AAOS Now. Dr. DiGiovanni recommends these articles for any patient considered a candidate for either of these two options.

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