Ankle replacement is rapidly becoming a comparable option to ankle fusion in the treatment of ankle arthritis. Although ankle replacements in the 1970s did not fare well, the new generation of ankle replacements has provided an excellent option in the treatment of ankle arthritis. Indeed, ankle replacement has proven to be a better option than ankle fusion in the proper situations.
Accordingly, let us take a closer look at the current options for ankle replacement, potential benefits of these devices and the current thinking on the use of the different ankle replacements available on the market today. It is important to remember that patient selection and proper placement of the implant are the keys to an ideal outcome.
In general, our institute reserves ankle fusion for younger, very active patients who require a great deal of strength and stability from their ankle. Ankle fusions are also preferred for cases of severe angular deformities that may not be correctable with ankle replacement. If the ankle is not well aligned and will not become well aligned with bony or soft tissue procedures prior to placement of the ankle replacement implant, we often perform an ankle fusion.
One should reserve ankle replacement for patients who do not perform heavy manual labor, are over the age of 45 (preferably over the age of 55) and have little to no ankle deformity. Although surgeons may correct some level of ankle deformity with soft tissue or bone realignment procedures, the ankle replacement patient of choice is one with an arthritic ankle that is well aligned.
Of interest is the fact that patients who have arthritic hindfoot joints about the ankle seem to do better with an ankle replacement than an ankle fusion. This is due to the fact that an ankle fusion places greater stress on the surrounding joints, which may lead to further arthritic changes of the hindfoot joints. In contrast, an ankle replacement allows motion at the ankle, resulting in less strain on the surrounding joints.
A Guide To The Preoperative Assessment
Patients will often present to our offices with a preconceived notion of what procedure is best for them. This is important to address early in the relationship with the patient. It is important to explain the two procedures (replacement versus fusion) in detail, and the risks and benefits of each.
One should ensure a thorough assessment of the patient’s vascular and neurologic status. If the circulation of the patient is poor, do not select an ankle replacement as the anterior incision and soft tissue complications associated with ankle replacement may not be in the patient’s best interest. Furthermore, a neuropathic patient with lack of sensation in the foot is not a good ankle replacement candidate and such cases have shown an increased rate of failure.1
The dermatologic workup requires an adequate check of the skin for breakdown and quality. If the skin is of poor quality, the anterior ankle has a skin graft or flap, or if there are severe varicosities, these may be possible contraindications to ankle replacement.
Finally, check the function of the muscles, ligaments, tendons and bones of the foot and leg prior to considering an ankle replacement. Address laxity about the ankle from previous ligament injury to build a solid platform for the replacement. If there is a non-functioning tendon, surgeons need to ensure the pull about the ankle is ideal. Finally, alignment of the bones must be ideal or surgeons should correct this prior to pursuing ankle replacement.
In most cases, standard radiographs are sufficient to assess whether a patient is a viable candidate for ankle replacement. Check alignment and bone stock as well as the level of arthritis at the ankle and surrounding joints. If there is a potential for cystic changes in the talus or tibia, or signs of avascular necrosis, one may order a magnetic resonance image (MRI) or computed tomography (CT) scan to assess the ankle joint further.
In the case of avascular necrosis, as long as the majority of the talus is unaffacted, one may perform an ankle replacement. If the talus is very damaged, an ankle fusion may be a better option. If there are severe arthritic changes of the joints surrounding the ankle, the patient may need a hindfoot fusion and ankle replacement.
Weighing Mobile Bearing Versus Fixed Ankle Options
Currently, our institute utilizes two different ankle replacement options. The INBONE® Total Ankle Replacement (Wright Medical) is a fixed ankle replacement while the Scandinavian Total Ankle Replacement (STAR™, Small Bone Innovations) is a mobile bearing option. We have seen excellent results with both devices and they both have pros and cons.
In regard to the main difference between a fixed and a mobile bearing ankle replacement, with the mobile bearing option, the plastic spacer material is not attached to the talar or tibial component, and floats in between the two. This allows for some varus and valgus tilt, and there may be less stress during movement on the metal-bone attachment point of the implant. This results in less loosening. The fixed option has a plastic spacer, which is attached to the tibial component. This spacer does not allow varus or valgus tilt, but allows for a long stem insertion into the tibia. This may add strength and prevent subsidence.
The choice of implant is a difficult one to make. The STAR implant is a very low profile device and has an excellent potential for conversion to either a fusion or larger ankle replacement in the case of a problem. On the other hand, the INBONE option has a good implantation guidance system and the long tibial stem allows for strong tibial stabilization. In our experience, both systems have had excellent results and are fairly easy to insert after one masters a learning curve.
In our institute, we have begun to use the STAR ankle replacement in stable and simple ankle replacement cases that require minimal soft tissue or bony procedures. The STAR also has a more stable talar component, which we prefer in cases of severe talus arthritic changes or severe medial and lateral gutter arthritis. It is still unclear if there is a major benefit to a three-piece mobile bearing implant.
On the other hand, if there are any cystic changes in the tibia or if there is a previous distal tibial fracture and the bone is not ideal, we prefer the INBONE ankle replacement as it has a far more stable tibial component. Also, the INBONE ankle replacement has a better surgical guidance system, which allows better positioning in more difficult ankles. Finally, in the case of a previously failed ankle replacement that requires revision, the INBONE is our preferred system.
Patient selection and proper surgical procedure are essential for ideal outcomes with ankle replacements. With the continued advancements in ankle replacement options, further research and clinical experience will confirm which procedure and replacement material is best for each type of patient.
In general, we prefer the mobile bearing ankle in straightforward cases or cases with severe talar damage or medial/lateral gutter arthritis. We prefer the more stable fixed bearing option for tibial cystic changes, deformed tibias, revision cases or more difficult alignment cases. Both replacements have worked very well and have proven to be excellent additions to our practice with many happy patients.
Dr. Baravarian is an Assistant Clinical Professor at the UCLA School of Medicine. He is the Chief of Podiatric Foot and Ankle Surgery at the Santa Monica UCLA Medical Center and Orthopedic Hospital, and is the Director of the University Foot and Ankle Institute in Los Angeles.
Dr. Morris is a faculty member of the University Foot and Ankle Institute, and practices in the Santa Barbara Institute.
1. Deorio JK, Easley ME. Total ankle arthroplasty. Instr Course Lect. 2008; 57:383-413.
Editor’s note: For further reading, see “Inside Insights On Ankle Replacement Surgery” in the March 2008 issue of Podiatry Today.