WASHINGTON, May 28 — The FDA has approved a system for replacing ankle joints deformed by arthritis that may preserve a greater range of motion than fusion surgery.

The Scandinavian Total Ankle Replacement (STAR) system, manufactured by Small Bone Innovations, is a mobile-bearing device consisting of two metal plates with bars that fit into the bone and a polyethylene spacer that moves between the plates like a ball bearing.

It is the “first of its type,” according to the FDA, which has approved several fixed-bearing devices in which “the articulating surface is molded, locked, or attached to one of its metallic components.”

The STAR system “more closely imitates the function of a natural ankle,” according to Daniel Schultz, M.D., director of the FDA’s Center for Devices and Radiological Health.

It represents an alternative to fusion surgery, which involves cementing the tibia to the talus bone in the ankle, reducing the ability to move the foot up and down.

The approval was based, at least in part, on a study of 224 patients who were followed for at least two years. Those who were fitted with the STAR system had rates of adverse events, surgical interventions, and major complications similar to those in patients who had fusion surgery, according to the FDA.

As a condition of the approval, the device maker must evaluate the safety and effectiveness of the device over the next eight years.