The results of ankle replacement are better than ever. Researchers at the University of Minnesota have found a way to measure true ankle motion to prove this.

Until now, other studies reported measures of the ankle, midfoot, and hind foot motion. True ankle joint motion is measured where the tibia (lower leg bone) meets the talus. The talus forms the lower part of the ankle dome. The point where these bones meet is the tibiotalar joint.

The ankle has several different motions. Normal ankle motion allows the foot to point down a full 50 degrees. This motion is called plantarflexion. Pulling the toes up toward the face is called dorsiflexion. Most adults can dorsiflex about 20 degrees. Both motions are needed for walking and going up and down stairs.

In this study, all ankles were X-rayed with the patient in the standing position. A second X-ray was taken from the side with the ankle in both full dorsiflexion and full plantarflexion. X-rays were taken before and after the joint replacement. This method allowed researchers to detect motion at the true ankle joint.

Everyone got the same type of ankle implant, called the Agility Ankle. Results of this study showed that patients had five degrees more true tibiotalar motion after the operation. This was enough motion to allow the patients to walk normally. There were still some problems going up and down stairs.

The authors think patients should be told before the surgery that the benefit is mostly pain relief. The increase in ankle motion isn't especially good. Final ankle motion is based on ankle joint motion before surgery. Most patients do seem able to make use of the motion they have when the pain is gone.