By Jane Ehrhardt
“If you have a patient with a severe deformity or odd anatomy, you can actually have custom implants made now,” says John Kirchner, MD about the total talus procedure. Kirchner, an orthopedic foot and ankle specialist with Southlake Orthopaedics has performed around 400 total ankle replacements over his career and says the advancements keep coming.
Total ankle replacements began in the 1980s. But the first ones loosened easily and were abandoned. “In the early 2000s, it resurfaced with an implant that started restoring more natural anatomy, range of motion, and preserving a mobile joint itself,” Kirchner says. However, if not set in perfectly, it resulted in loosening and subsidence, where the implant actually sinks into the bone.
But 2006 brought a breakthrough. “The way you cut the bone changed,” Kirchner says. “Instead of making just one big flat cut on the bone, we were doing angled cuts.” Then came patient-specific cut guides, and a new generation of replacements came about.
The personalized cutting blocks, based on CT scans and built-in 3D printers, are pinned in place on the patient to guide the saw blade as it cuts the bone. “You have much more precise cuts,” Kirchner says. “The saw can’t twist on you easily so it can’t glance off and make a little bit of an incorrect cut.
“That precision has drastically cut surgery time. When I learned how to do this in the late 1990s, it took up to three hours for a simple ankle replacement. Now the implants are better and with the guides in position, it doesn’t take as long to get the resections done and the implants in. The surgery now takes around 45 to 60 minutes.”
Though the cuts are personalized, the implants generally come in an array of standard sizes. However, custom implants can now be made, as well. The Kinos replacement system uses 3D printers, making customization cheaper and far quicker.
The implants have not yet advanced enough to imitate all the movements of the natural ankle. “They don’t do side-to-side motion as such, but they have better mobility and longer survival than past implants,” Kirchner says.
Even the standard implants can offer better range of motion than most patients may expect. Some of that motion is a coupled inversion/eversion or swinging under/swinging out motion of the foot. “Because the cuts are more precise, you don’t take away as much of the bone, and you could actually preserve some of the natural motion from other joints that are still there,” Kirchner says.
Though they generally mitigate much of the pain suffered by patients, the implants still result in restrictions, primarily in impact activities, like running or jumping. “But most of the patients that need replacements have already altered their lifestyle because of the pain,” Kirchner says.
These newer implants generally last 12 to 15 years with good care, although even careful people can face a traumatic fall or car accident that disrupts the implant. But advances in revisions have created options. “Say you fall and your shin component has to be revised,” Kirchner says. “You can go from a standard to a custom-built implant component to compensate for the damaged bone.”
These highly customized revisions and the flexibility offered by 3D printers have opened up the possibility of total replacements to people who were previously denied the option. “Some of what couldn’t be done in the past with big bone voids or big angular changes can now be addressed,” Kirchner says. “These could be angular problems because of the way the bone healed when you had your original injury. And now we can address that more easily with the accurate placements.”
The revisions are not so advanced yet as to change the restrictive eligibility guidelines. With the implants lasting up to 15 or so years, most patients are told to wait until their 50s or 60s. “Ankle replacements are sort of a double-edged sword. You can’t keep replacing it, because of the bone,” says Kirchner. “Every time you replace it, you have to cut a little more bone to get a stable surface so the implant can stay on.”
The current alternative for ineligible candidates, no matter the reason, is to endure the pain and mobility challenges for potentially decades or get their ankle fused. That means when their age or advances in replacements makes them eligible, they still don’t qualify.
Kirchner sees that as the next challenge for the field. “You got your ankle fused in your 30s, back when we didn’t have any replacements, or got it fused after a fall,” he says. “Now you need to regain that mobile segment because other parts of your body are breaking down as the strain on backs, knees, and hips accrues over decades of compensating for a damaged ankle. We need to start thinking about patients with prior ankle fusions. What can we do with those who now need to get that motion back because of other physiologic comorbidities?”
