Almost 6 million Americans are living with either an amputated limb (about 2.3 million) or a congenitally different limb (about 3.4 million). For centuries, the prostheses available for these people have connected to the outside of the leg, arm or other extremity using a sling or socket. But in the coming decades, osseointegration—connecting implants directly to the bone—promises a revolution in the field. Cedars-Sinai is one of the few facilities in the country currently performing the surgery.

It’s only in the past few years that providers have had success attaching an exterior prosthesis directly to the bone of an amputated or congenitally different limb. There are different ways to make the connection, but so far only one of them is approved by the Food and Drug Administration.

“You screw the device into the bone, and that holds it stable enough for the bone to grow onto it,” explained orthopedic surgeon Geoffrey Marecek, MD. “Then we have what’s called an abutment, which sticks out through the skin and is able to connect to the prosthesis.”

A number of problems associated with traditional prostheses can be avoided with ones that are anchored directly to the bone.

“Traditional prostheses were never completely ideal and never completely stable,” said Mark Vrahas, MD, chair of the Cedars-Sinai Department of Orthopaedics and the Levin/Gordon Distinguished Chair in Orthopaedics in honor of Myles Cohen, MD. “You have problems with skin breaking down, and you have problems with them not being tight enough to allow real types of mobility, such as running and that sort of thing.”

“When it’s really hot and humid—it’s really sweaty—it can be really irritating to the skin,” added Marecek. “There also can be issues with pieces of bone or other things inside pushing on the socket, and so patients [with traditional protheses] get these sore spots or areas where they can’t support their weight.”

Bone-anchored prostheses can also improve proprioception, which is when a person receives feedback from their limb.

“Walking on a completely insensate foot that is attached to a piece of plastic that is then attached to the outside of your skin doesn’t give you much direct feedback from the ground when you’re walking,” Marecek said. “But with a bone-anchored prosthesis, patients begin to be able to tell the difference between walking on hardwood versus carpet and different surfaces. People can walk on uneven ground or up a rocky hillside, which is difficult in a conventional prosthesis.”

The doctors agree that the main concern is infection.

“We don’t typically have metal things sticking out of our body,” said Marecek. “And right now, there is a 10% risk of needing to have [the osseointegrated prothesis] removed due to infection or other complications.”

That is unusually high for orthopedic procedures, which typically boast 99% success rates.

The procedure is still considered new and experimental, and patients often struggle to get it covered by their insurance company.

“There are a lot of unknowns and uncertainty,” said Marecek. “But the potential to help people is enormous. And so, over the next 25 years, I think osseointegration will become very commonplace and very routine.”