I understand that ankle replacements are kind of like the new kid on the block. I’ve been told results aren’t as good as with a hip or knee. Still, it seems like it’s worth a try. My ankle hurts so bad now I’d like to cut the whole thing off. But there’s always that nagging doubt in the back of my mind. Should I or shouldn’t I do it?

All of the major joints can be replaced now: the shoulder, hip, knee, and ankle. Surgeons have the most practice with hips and knees. Ankles remain more difficult because of the complexity of the joint itself. Patients may get good pain relief with ankle joint replacement but they don’t always get better ankle motion.

Lining up all the bones and parts of the implant can be very challenging. Experts say there is a “steep learning curve” for the surgeons doing this procedure. That means their early attempts aren’t as good as their later cases after they’ve had the chance to do many ankle joint replacements. They do practice on cadavers and that is an important step in learning how to do these procedures.

But getting the right alignment, correcting any anatomic deformities, and repairing damaged soft tissues can be very complex and challenging — even for the most seasoned surgeon. For example, the axis of rotation depends on perfect alignment of the talus (one of the major bones replaced). But even in normal ankle joints, this axis changes during motion. Duplicating normal anatomic alignment and function is a complex and demanding step in the ankle joint replacement procedure.

Skillful use of fluoroscopy (real-time X-rays) is required for this procedure. The surgeon works hard to achieve a zero anteroposterior offset ratio. Patients have much better outcomes (pain, ankle motion, and ankle function) when this ratio is zero.

What is the anteroposterior offset ratio? It is a measure of the relationship between the two key components of the ankle joint implant. There is the flat piece that goes at the base of the tibia (shin bone) called the tibial plafond and the replacement for the talus (the bone at the top of the ankle that moves against the tibia).

When the center of the talus lines up with a vertical line drawn down the side of the tibia, the anteroposterior offset ratio is zero. That is a perfect line up of the two component parts. If these two points don’t line up, then there can be a positive ratio (measure greater than zero) or negative ratio (measure less than zero).

The key to a good result is improving the alignment and mimicking normal biomechanics as much as possible. Patients are advised before surgery that even with the newer improved implants, results aren’t always as expected. The change in ankle motion can be very small. Pain may be reduced and even gone but there is the chance that pain will persist.

Studies show that even in the hands of experts, zero anteroposterior offset ratio is possible in less than half the cases. Small malalignments can cause stress on the soft tissues around the ankle and the other bones of the ankle and foot. Even minor increases of strain on the ligaments can cause pain and loss of motion.

Having the right expectations and understanding of the possible outcomes before having this procedure done is important. It sounds like you have been well-educated on the pros and cons of ankle joint replacements. We hope this added bit of information will help you discuss your situation with your surgeon and make the best choice for you.