A Complete Guide to Bionic Legs & Feet

Everything you need to know about bionic legs, knees, ankles, and feet. Continuously updated, this page is your one-stop repository for all the latest information on lower-limb devices, technologies, and research.

What’s On This Page?

What is a Bionic Leg?
Understanding the Technical Challenges for Bionic Legs
Surgical Procedures
Current Bionic Ankles & Feet
Current Bionic Knees
Current Full Bionic Legs
Open Source Bionic Legs & Feet
Latest Research Articles
User Satisfaction Reports
Bionic Feats
Real Stories
Related Information

What is a Bionic Leg?

A bionic leg is an electromechanical device that attaches to the human body via a socket and attempts to replicate the functionality of a natural leg.

It always consists of sensors, a microprocessor ankle/foot or knee, and at least one battery.

Some devices, such as Blatchford’s Linx bionic leg, have all of these components:

Understanding the Technical Challenges for Bionic Legs

The Basic Mechanics of Walking

When humans walk, each leg alternates between a Stance phase (the foot has contact with the ground) and a Swing phase (the foot is off the ground). These phases can be divided into sub-phases:

Source: https://www.researchgate.net/figure/Human-gait-cycle-28_fig1_324346331

During this gait cycle, the body employs several biomechanical functions including:

shock absorption by muscles, tendons, ligaments, and cartilage from the moment of Heel Strike until the full body weight is assumed by the Stance leg;
antagonistic muscle pairs to move the foot, ankle, knee, and hip into the desired positions;
the use of elastic energy as tendons and muscles stretch during the first half of the Stance phase, then recoil to help begin the Swing Phase;
muscle contraction to lift each leg and propel the body forward.

Most of these functions have mechanical equivalents such as dampers, springs, actuators, etc. The challenge is controlling and coordinating them in a smooth, integrated manner.

Bionic Leg Control Systems

When we humans approach an obstacle like stairs, we glance at them to gauge their height, steepness, tread width, etc. To climb the stairs with natural legs, we automatically adjust our stride, foot placement, joint angles, and muscle power. This is possible because of our brain’s ability to:

perceive a 3D map of its surroundings including the terrain;
use proprioception to maintain a keen sense of our body’s position within that 3D map;
precisely adjust and control the movements of hundreds of muscles.

The bionic legs and feet currently on the market do not attempt to replicate this sophisticated system (though the new Agonist-antagonist Myoneural Interface (AMI) technology may help close the gap). Instead, their sensors gather information like walking speed, joint angles, etc. Microprocessors then use this data to automatically adjust settings such as joint resistance, sometimes hundreds or even thousands of times per second.

These systems are localized, reactive, and completely independent from the human brain. Yet, they have proven to be remarkably successful, as shown in this short video of a double amputee walking and running up a set of stairs:

Still, users want more. They want improved user control over their bionic limbs, sensory feedback, and even power-assisted propulsion.

To learn the status of many of these objectives, please see our full article on control systems for bionic legs and feet.

Surgical Procedures

For thousands of years, amputations served only one purpose: to sever a damaged or diseased limb. Little thought was given to preparing the residual limb for an eventual prosthesis.

This situation has changed dramatically over the past two decades. Surgeons now have procedures to:

reassign severed nerves for reduced limb pain and improved muscle control in the residual limb;
reconnect severed muscle pairings to restore proprioception;
implant myoelectric sensors to improve the detection and interpretation of muscle movements;
attach electrodes to nerve bundles to facilitate sensory feedback;
insert a metal rod in one of the major leg bones to act as a superior prosthetic connector and eliminate the need for a socket;

Indeed, these procedures have advanced to the point where they should now be considered by new and existing amputees alike. To learn more, see Surgical Techniques That Improve the Use of Bionic Limbs.

Current Bionic Ankles/Feet

Bionic ankles/feet are responsible for the following tasks:

automatically adjusting the resistance in the ankle to ensure the proper level of support through each stage of the Stance Phase regardless of terrain;
keeping the foot “toes” up during the Swing Phase to create more clearance and reduce the risk of tripping;
some bionic ankles also actively manage the ankle rotation (i.e. foot angle) based on terrain, and one (the Empower Ankle) provides added propulsive power.

The main bionic ankles/feet currently on the market are:

This promotional video from Blatchford provides an excellent technical description of the end-user benefits from such devices, starting at 1:10:

Unfortunately, it is difficult to find independent, first-hand consumer reviews of bionic ankles/feet, though we have begun to add a few of these to our device articles. Most material on the subject is still either promotional or scientific.

Until that situation changes, we’ll settle for showing the latest advances such as this bionic ankle/foot for more active amputees:

Bionic Ankles/Feet Affordability

Based mainly on user feedback, most bionic ankles/feet sell for between $18,000 to $25,000 US. This makes sense given that the Medicare/Medicaid reimbursement rates are around $18,000 US for this type of device.

The most expensive bionic ankle/foot is Ottobock’s Empower Ankle, which sells for between $40,000 to $50,000 US. That’s quite a leap in price, but if you watch our videos on the Empower, it’s also quite a leap in technology.

For more information, see our Bionic Foot Price List.

Current Bionic Knees

Bionic knees are responsible for the following tasks:

automatically adjusting the resistance in the knee to ensure the proper level of support through each stage of the Stance Phase regardless of terrain;
ensuring the optimal release point for the knee to begin the Swing Phase and the proper knee extension/damping at the end of this phase;
assisting in stumble recovery.

The main bionic knees currently on the market are:

Again, it is difficult to find independent, first-hand consumer reviews of bionic knees. But this video of a young man using one of the most advanced knees — Ottobock’s Genium X3 — at least provides a glimpse of their potential:

Paired with the correct prosthetic foot, there are obviously few limits on the use of this knee. So, with a knee like this, why would someone need a bionic ankle? First, using the knee alone is more tiring without the assistance of a bionic ankle. It also isn’t as smooth when walking up or down stairs or other inclines.

This of course leads to the question: what happens when you combine these two technologies? We answer this question below.

Bionic Knees Affordability

Based mainly on user feedback, most bionic knees sell for between $20,000 to $50,000 US.

The most expensive bionic knee is Ottobock’s Genium X3, which can cost more than $100,000 US depending on the prosthetic foot that is paired with it, warranty extensions, etc.

For more information, see our Bionic Knee Price List.

Current Full Bionic Legs

There is only one bionic leg we know about that fully integrates a bionic knee and ankle. This is Blatchford’s Linx:

It is inspiring to see amputees being so physically active. It’s proof that, technically, we are getting close to eliminating lower-limb disabilities.

The problem is one of availability. This is limited not only by price but also by insurance policies.

For example, Ossur combined its Rheo bionic knee with its Proprio bionic ankle to create a Symbionic leg product but the resulting product had poor sales. Why? Because public and private medical insurance resisted paying for it.

Bionic Leg Affordability

The Linx sells for between $60,000 and $70,000 including the socket and all prosthetist fees.

Open-Source Bionic Legs & Feet

For decades now, the open-source approach has flourished in the software industry. It works by allowing the entire user community to contribute to software solutions. It speeds up innovation, reduces costs, and fosters standardization. Just on the issue of standardization alone, this makes software more modular and easier to reuse.

Now compare this to the world of bionic legs & feet. Even though the tasks faced by one bionic limb manufacturer are quite similar to those faced by another, many take a proprietary approach. This has the unfortunate effect of slowing progress and making end products more expensive.

Fortunately, the University of Michigan is spearheading an Open-Source Bionic Leg initiative.

The objectives for this program are not yet as far-reaching as a typical open software initiative, as it is focused more on standardizing aspects of the R & D process. But the benefits of this approach will ultimately trickle down into the commercial market.