Is the Solution to a Painful Ankle Fusion an Ankle Replacement? Vice Versa?

Yes. I think keeping as much of the native anatomy in place is important for many reasons. First, it does allow for easier conversion from fusion to total ankle replacement (TAR) at a later date if the need should arise. We can debate how often or common this might be needed, however. Second, cosmetically and for shoe-fitting purposes, the ankle seems to look and feel more normal if the fibula is left intact, and third, an anterior approach fusion using an anterior fusion plate with lag screws outside the plate is the most reliable and stable fusion construct in my hands. Unless there is significant deformity requiring removal or concern of chronic infection, I leave the fibula intact and, in fact, try to leave the medial and lateral gutters intact as well.

In the past when it was more common for me to take the fibula down, I did see some cases wherein the hindfoot seemed to drift into valgus over time. Whether that was actual a positional change of the hindfoot or just the appearance since the medial malleolus seemed larger as there was no counterbalance visually of the fibula. Today, if I need to take the fibula down for some reason, I will more likely do a tibiotalocalcaneal fusion instead of an isolated ankle fusion.

Fusion takedown is still relatively rare in my practice, and I perform very few fusion takedown conversions to TAR. In the cases I have done, it has been for reason for painful malunion/malposition of the ankle or painful significant adjacent joint arthritis, which would require a pantalar fusion, or adjacent joint fusions, which are notoriously hard to heal under an ankle fusion and functionally are quite limited when combined together.

In these limited takedown to TAR cases, I think it is important to really keep expectations in check. These TARs frequently are still quiet stiff secondary to all the surrounding tissue contracture from the fusion and do not perform like a primary TAR. The function here really is not to be a “normal” ankle but just to have some motion, enough to unload stress on the surrounding joints, reduce pain, and hopefully improve function.

In my practice, the vast majority of patients with end-stage ankle arthritis under the age of 50 are treated with an ankle arthrodesis rather than arthroplasty. Unless they have comorbidities/characteristics that render them unlikely to ever be a candidate for fusion takedown (eg, super morbidly obese, gross neuropathy, etc), I utilize an anterior fibula sparing ankle arthrodesis approach. To date, I would say that a minority of patients that have had a prior ankle arthrodesis eventually request fusion takedown with conversion to arthroplasty. These patients tend to fall into 2 categories: (1) patients who have been lost to follow-up for years and then return with painful hindfoot arthritis or (2) patients who received an ankle arthrodesis at a younger age and had been expecting a fusion takedown once they reached a certain age.

I would also note that I commonly see patients that have had a prior fibular sacrificing ankle arthrodesis 20 years ago in the community who eventually develop severe symptomatic subtalar arthritis. Although some surgeons have described fibular allografting in this scenario, in my practice, prior fibular resection is a contraindication to arthroplasty conversion. Many of these patients are frustrated that this is not an option to them based on their prior surgery. Thus, even if only a minority of my patients ever eventually undergo conversion from a successful arthrodesis to arthroplasty, I still feel it is best practice to leave the fibula in place during arthrodesis to leave as many options open as possible in the future.

I think the point of this question is well taken. We have been fairly limited in TAR revisions options until relatively recently. Now there are several systems that allow for revision to stemmed implants on the tibial side, metal augments to replace volume deficit on either side of the joint, revision poly sizes, and broadened fixation options around the talus to try to anchor into stable bone. These systems do make salvage and revision of TAR much more possible without necessarily having to convert to tibiotalocalcaneal fusion as the only option.

Revision and conversion to another TAR really depends on the mode of failure and the subsequent collateral damage that may have occurred. To this point, it is strongly recommended that regular, routine surveillance of TAR patients is done on an ongoing basis so that any early signs of implant failure can be detected and addressed before they have more serious complications. In our practice, we routinely see our TAR patients yearly until 5 years out and then every other year after that if everything looks good. The patients need to be partners in this surveillance routine, even if everything feels great. Often early implant loosening, cystic change, and bone erosion may occur without much in the way of pain, and the patient only feels something after that such as more significant bone collapse or pathologic fracture which obviously complicates the revision picture.

The decision to revise to another implant versus conversion to fusion is also variable case by case and may depend on the exhaustion of both patient and surgeon up to that point. Sometimes patients just prefer conversion to a fusion if it seems like a more final and definitive option to just be done with the whole process. Obviously fusion after failed TAR is not necessarily a slam dunk either, but in some cases may be more final.

I would agree that the advent of reproducible revision arthroplasty systems has afforded us the ability to salvage failed ankle implants in a way that was not possible in the past. However, a failed total ankle arthroplasty, particularly in the case of significant talar bone loss/subsidence, remains a very difficult clinical scenario. After removal of the failed implant, there is still controversy about the best way to handle the large bone void during conversion to arthrodesis. It is usually very difficult to achieve simple tibiotalar arthrodesis in this scenario and they must be converted to a tibiotalocalcaneal arthrodesis, typically with an intramedullary rod barring deep active periprosthetic infection.

In the past, I typically used a contoured femoral head allograft in this situation. Disadvantages of this technique include the use of a large bulk nonvascularized foreign tissue mass, and loss of construct strength during preparation/cannulation with an intramedullary rod. In the past several years, I have largely abandoned that technique. Now, I typically use a custom 3D-printed cage based on a CT (computed tomography) of the contralateral limb, cannulated in the central portion to accept an intramedullary rod. These constructs can be packed with bone graft, both allograft and autograft, often with a combination of bone marrow aspirate concentrate and/or commercially available bone growth proteins. Advantages of this technique include the immediate intrinsic strength of the metal cage, coupled with a 3D-printed ingrowth surface to facilitate long-lasting bony incorporation.

In rare cases, for example, if the patient already has significant collapse/chronic shortening, I will perform a direct tibiocalcaneal arthrodesis with direct bone to bone contact. This has the advantage of the highest chance of achieving successful union, at the cost of resulting in the significant leg length discrepancy that often needs to be treated with permanent shoe lift modifications.

The research in total ankle arthroplasty (TAA) has evolved over the years from mostly a question of clinical outcomes and patient satisfaction to an area of research in which we are beginning to explore the impact of this surgical option on physical function and gait mechanics as well as exploring how TAA could impact other joints in the foot as well as throughout the lower body. Early in this work questions were simple and relied on asking questions simply about how patients perceived their results, which meant that with pain relief we saw huge improvements in patient-reported outcomes. As we began to explore TAA more fully it was clear that joint replacement did not return “normal” locomotion and in many cases made no change. While there was no change in joint mechanics it also meant that the patients were not losing motion as was seen in ankle fusion. These results left us in a position to begin to ask more questions about the TAA from understanding how the procedure affected energy exchange (surrogate for fatigue) as well as joint power production while exploring questions of compensatory patterning. Through this work we have begun to explore potential areas for intervention to improve long-term joint health and decrease the risk of additional joint replacements and improved mobility.

We have done a little work in analyzing gait in patients with an ankle fusion takedown and have data available in a larger dataset that could be explored further to really understand this special type of TAA. The only work in which we have begun to explore this patient population was an abstract that was presented at the 2019 AOFAS (American Orthopaedic Foot and Ankle Society) annual meeting. In that study, which included a very small sample (10 fusion takedown and 7 TAA with subtalar fusion), we found that the fusion takedown group had improvements in gait mechanics, specifically sagittal plane ankle ROM (range of motion) when compared to the subtalar fusion group. There is a need to expand this sample and to understand the difference in postoperative recovery i TAA only patients and those who received a TAA following an ankle fusion. We will be looking into this line of research further as we continue to understand TAA following a fusion and as a revision procedure.

Given the limited scope of our research in the area, I am not sure that we know yet how recovery differs between these 2 groups. It is clear from the larger samples we have analyzed that TAA is able to resolve pain, improve walking speed, and improve side-to-side symmetry. The level of improvement appears to be very dependent on the patient and the level of gait dysfunction prior to joint replacement surgery. The areas of physical rehabilitation following surgery as well as the role of pre-habilitation in this patient population have yet to be explored. It is possible that with increased emphasis on gait retraining and improving muscle strength and function we can improve both short-term and long-term outcomes following TAA for both primary surgical cases as well as revision surgeries.

Many prior studies have shown superiority of ankle arthroplasty in comparison to ankle arthrodesis in terms of gait analysis and functional evaluations. For example, in general it is accepted that patients have a more normal gait pattern following ankle arthroplasty compared to ankle arthrodesis, although it does not return to a normal baseline. There are also multiple validated functional assessments (eg, four-square step-test times, sit to stand times) suggesting superiority of arthroplasty over arthrodesis. Anecdotally, my practice will support these findings. Ankle arthritis comprises a significant portion of my practice, and I would estimate the ratio of arthroplasty versus arthrodesis is 4:1. Although prior data have suggested equivalent pain relief following arthroplasty and arthrodesis, from observing my patients from their first postoperative visits to later follow-up dates, patients with ankle replacements tend to have better pain relief and walk more normally compared to those after arthrodesis.

Subjectively, my patients who have undergone ankle arthrodesis takedown tend to have more stiffness and perhaps lower functional outcome compared to those with primary arthrodesis, which is unsurprising for multiple reasons. One, their soft tissue envelope has contracted during the time of arthrodesis and it can be difficult to achieve a broad range of motion even with a well-placed prosthesis. Two, some of them receive adjunct procedures at the time of takedown (eg, subtalar arthrodesis). However, I would also note that these patients are often among happiest with their outcome.

I discuss this concept with the patient during our consult for possible TAR versus fusion. Most of the studies I have read demonstrate that TAR is more normal than fusion but not really as normal as a native, non-arthritic ankle. So, I reiterate to them that the TAR will be closer to normal than the ankle is currently with DJD, will be closer to normal than if fused, but it will not be the ankle of 20 years ago. This seems to make sense and sets a reasonable expectation.

In my clinical experience having both types of patients, the ankle fusion patients actually report they function quite reasonably early on. I would say for the first 5 to 10 years, ankle fusion patients do well. They are mostly out of pain. They can do most activities of daily living and hobbies. They usually tell me they walk a little slower than “normal” but were already walking slower before the fusion secondary to the arthritis and pain. They do usually have some difficulty going up and down inclines and sometimes with really uneven ground as well.

The challenge comes in 10 years or so after the ankle fusion if the surrounding joints start to stiffen up and become arthritic. This is when they really start to have significant limitations and the situation is much more difficult to control.

On the flip side, most of the TAR patients seem to bounce back into a more “normal” life by about 6 months. They really can do almost any activity they want to, and in fact, most of our conversations usually revolve around remaining “joint protective” with their activity level and choices. I remind them the TAR is a moving, mechanical part. The easier they can be on it, the longer it is going to last. I try to keep them to low-impact activities like walking, hiking, golf, cycling for the most part.

As I said earlier, I do not expect these kinds of outcomes though in the long-standing fusion that has been converted to a TAR. There is just too much surrounding soft tissue contracture and associated muscle atrophy from being fused. In my experience, the converted TAR really functions more like a passive hinge rather than a highly active and functional segment. Still, in the right case, this can be a significant benefit and pain relief.