Monday, June 1, 2015

Developments in Total Ankle Replacement

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 surgical intervention as well as the many joints and complex biomechanics that characterize the region. Fusion has seen much wider practice, with its union rate of roughly 90%, after which significant pain relief is generally reported.

Arthrodesis of the ankle, however, can disturb the gait pattern and lead to stress of nearby joints (1). Tertiary care orthopedic foot and ankle specialists are pursuing innovations in total ankle arthroplasty (TAA) that are likely to promote its wider adoption. Christopher DiGiovanni, MD, chief of the Foot and Ankle Service 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 a new generation of ankle replacement devices and protocols. While ankle replacement has not compared favorably 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 ankle replacements under more recent guidelines show a postoperative survivorship of 80% to 95% over 5 to 10 years.

Ankle Replacement Imaging

Ankle Replacement Imaging
Left: This X-ray shows a total ankle replacement in the process of insertion. The prosthetic joint here is the Eclipse, designed by Christopher DiGiovanni, MD. The image also captures instrumentation for insertion, including a cutting jig designed to remove arthritic bone from either the medial or lateral side in preparation for implant insertion.
Right: This X-ray shows a patient with bilateral ankle arthritis, with subsequent surgeries. On the left is an arthrodesis of the ankle, fusing it in place. On the right, the patient has an implanted ankle prosthetic, which allows for near-normal movement.
Source: Christopher DiGiovanni, MD

Iterative Improvements in Prosthetic Design

First- and second-generation ankle prosthetic designs presented constraint issues and limited function, causing them to be either too restrictive or too unstable, leading 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.

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 longevity. The results, says Dr. DiGiovanni, are more reproducible gait cycle, better implant function, greater postsurgical activity and, most important, fewer significant complications or need for 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 typically put in as press-fit designs and 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, as these implants are smaller than those of hip, knee and shoulder replacement, yet by virtue of location must do more work. Slight inaccuracies in this area can have large consequences on implant durability, such as subtle foot malalignment, instability or stiffness (2).

Given the growing patient demand for TAA, clinician-scientists now appreciate a parallel need for setting proper functional expectations presurgery. Dr. DiGiovanni and the team at Mass General recently conducted a cross-sectional survey of fellowship-trained orthopedic foot and ankle specialists across the United States, published in Foot and Ankle Surgery in January 2015, which was designed to analyze the athletic and routine activity of daily living restrictions physicians place on patients following ankle replacement surgery (3). 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 also calls for the study of long-term effects. In conjunction with the Biomechanics Laboratory 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 important, the effects that foot malalignments—such as flatfoot or high-arch deformity—instability and stiffness might have on TAA kinematics.

References

(1) Ritterman, Scott A, Todd A Fellars, and Christopher W DiGiovanni. "Current Thoughts on Ankle Arthritis." Rhode Island Medical Journal, vol. 96, no. 3 (2013): 30-33.

(2) Greisberg, Justin, Sigyard T Hansen Jr, and Christopher W DiGiovanni. “Alignment and Technique in Total Ankle Arthroplasty.” Operative Techniques in Orthopaedics, vol. 14, no. 1 (2004): 21-30.

(3) Macaulay, Alec A, Scott M VanValkenburg, and Christopher W DiGiovanni. “Sport and Activity Restrictions Following Total Ankle Replacement: A Survey of Orthopaedic Foot and Ankle Specialists.” Foot and Ankle Surgery, accepted February 2015.

Contributor

 
This article first appeared in the Spring 2015 issue of Advances at Mass General.

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