Keys To Considering Ankle Replacement In The Treatment Of Ankle Arthritis
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.