Early designs for lower limb prosthetics focused on restoring basic movement. There have been advances enabling greater functionality, but these systems are still based on preprogrammed motions using limbs physically separated from the body. Shu et al. hypothesized that if connections could be formed between the soft and hard tissues and the lower leg prosthetic, then this would lead to greater stability and interfacing with the nervous system and enable more flexible and dynamic control (see the Perspective by Fisher). The authors demonstrated this concept by combining an above-knee prosthetic with an osseointegrated mount and an implanted control system to myoelectrially control the knee joint. With minimal training, the additional feedback provided to and from the knee made it easier for test subjects to avoid obstacles.

(Via Tissue-integrated bionic knee restores versatile legged movement after amputation.)

In his 1949 story The Cybernetic Brain, Charles Recour describes a kind of leg prosthetic electronic brain that resides in a prosthetic leg which is then connected to the user's own nerves:

Larry peered into the hollow leg, Dr. Schmidt handed him a flashlight. There was a complex arrangement of levers and racks and Larry could see them move as he flexed the leg at the knee and at the foot.

“This is wonderful,” he breathed staring at it admiringly.

“Show him the brain, Doctor," Joanne interrupted, “That will really startle him!”

(Cybernetic Brain from 'The Cybernetic Brain')

Dr. Schmidt reached in the wooden box and brought out a metal chassis similar to a small radio. Mounted on it were several tubes, coils and transformers. It was not very impressive. He set it on his desk.

“Larry,” he said, now grave, “if this will do what I think it will, it will be the greatest invention of the time. It is an auxiliary brain!”

“ — and we fit this little electronic brain and amplifier in the hollow of the leg, connect its output to certain servo-motors and relays within the leg. Into the input of the brain we connect nerve-endings from your thigh! The power supply comes from built-in batteries and electric capacitor-accumulators. In the bottom of the foot-portion of the leg is mounted a pressure sensitive device which will help control the leg — which will tell the brain and your body, when you are, dividing the weight between the real leg and the artificial one.”

“Am I to understand,” Larry asked incredulously, “that you’re actually going to connect my nervous system to a mechanical amplifier?”

"[Dr. Clydestone] will bring out the desired nerve endings from the end of the stump. He’ll connect them through platinum wires to little cable connectors... to seven nerve-endings protruding from his flesh, terminating, in ordinary electrical connections!"

But it was not the leg itself which was the real impressive agent; rather it was the electronic brain and the servo-mechanisms servicing it. Servomechanisms were simply electric or hydraulic motors whose motion was precisely controlled from a distance by electronic means.

The leg was to function, in a way, as a servo-mechanism operated by Larry’s brain, through the mediation of the electronic brain in the leg. It might be said that the artificial leg was a robot. Larry laughed at the thought. He was going to be actually made up of part-man, part-robot when the leg was finally fitted to him. But it was better by far than using the crude prosthetic devices ordinarily employed.

Dr. Schmidt had already designed every necessary mechanism for creating an artificial automatic, electro-mechanical, cybernetic leg.