Freedom Kinnex Foot / Ankle

Freedom Kinnex Feature Image

Proteor USA’s Freedom Kinnex is one of the most advanced bionic foot/ankle devices on the market. Rated as an IP67 device, it is both dust resistant and fully submersible in water.

What’s On This Page?

A Quick Look at the Kinnex

We prefer using third-party user videos to demonstrate the real-life functions of bionic devices. However, these two video commercials provide excellent footage of the Kinnex handling ramps, hills, and stairs:

For those of us looking forward to the day when technology eliminates all disabilities, the ease with which Kinnex handles these tasks is encouraging.

Kinnex’s Key Features

Ankle Range of Motion (ROM)

Kinnex offers 10 degrees of dorsiflexion (i.e. drawing your toes toward your shin) and 20 degrees of plantar flexion (i.e. pointing your toes away from your shin), for a total of 30 degrees of ankle articulation. This is more than Blatchford’s Elan, Ossur’s Proprio, Fillauer’s Raize, and Ottobock’s Empower foot/ankle systems, though less than Ottobock’s Meridium model.

Mechanical and hydraulic stops limit the ROM and stiffen the ankle for support and shock absorption, where needed.

Ankle Accommodation

Kinnex uses a within-step ankle accommodation strategy. This means that the ankle adapts to the terrain during the Stance Phase of each step. The alternative strategy is to adapt during the Swing Phase, but this requires multiple steps to adjust to changing slopes. 

Electric Propulsion

Kinnex does not provide any electric power to the foot/ankle to assist with push-off, but it does optimize energy storage and reuse through its carbon fiber foot plate.

The only bionic foot/ankle currently on the market that provides electric power to assist with push-off is Ottobock’s Empower model.

Sensor and Microprocessor Capabilities

Kinnex has 3 sensors:

  • Load Sensor, which detects how much load is being applied to Kinnex.
  • Torque Sensor, which detects how much forward/backward torque is being applied.
  • Angle Sensor, which detects the degree of ankle flex and calculates how slow or fast the ankle is rotating.

Kinnex also uses accelerometers and gyroscopes to provide inertial measurement data.

All of this sensor and inertial measurement data is fed into the unit’s microprocessor to automatically adjust the foot/ankle position according to the terrain, as well as to adjust ankle stiffness based on walking speed and step cadence.

Kinnex also accommodates varying heel heights up to two inches and allows users to program settings for up to 100 different shoes.

On even ground, Kinnex automatically adjusts the ankle’s dorsiflexion, plantar flexion, and ankle stiffness to mimic the motion of a natural foot/ankle. This provides superior shock absorption, which leads to a fluid forward motion and greatly reduces the stress on the prosthetic socket. The automatic adjustment of ankle stiffness also allows users to comfortably adjust their walking speed without disrupting their gait symmetry.

On uneven terrain, the biggest drawback of using fixed ankle devices is that the residual limb is exposed to unpredictable load changes. This increases the stress on the socket and makes it difficult for the user to maintain balance. Kinnex automatically compensates for uneven terrain with each step, eliminating both of these problems.

On ramps and steps, users of fixed ankle devices are forced to adjust their posture and motion because the prosthetic foot will not adjust. This increases the stress on the prosthetic socket as well as the load placed on the knee and hip of the intact limb, if present. Again, Kinnex automatically adjusts to eliminate the need for this unnatural compensation.

As shown in this next video, the ability to automatically adjust the angle of the foot/ankle makes sitting far more comfortable. It also makes it possible to place the prosthesis more directly under the center of gravity when getting up. Absent this ability, the user would have to shift most of the load onto the intact limb, if present.

In all of these scenarios, the benefit of the reduced load and stress on the prosthetic socket and residual limb cannot be overstated. Socket discomfort and related skin problems remain the number one reason for reduced prosthesis use.


Kinnex has a battery life of 24 hours. This is on the low end for bionic ankles but clearly sufficient for daily use.

If Kinnex runs out of power, it defaults to a manual lock mode, which essentially turns it into a fixed ankle system.

Water and Dust Resistance

Kinnex is rated as an IP67 device, meaning that you can submerge it in water for up to 30 minutes. It is also highly dust resistant.

Device Weight & User Weight Limit

Kinnex weighs 1,488 grams. This is similar to Ossur’s Proprio and Ottobock’s Meridium models, substantially less than Ottobock’s Empower, but substantially more than Blatchford’s Elan or Fillauer’s Raize models.

In theory, lighter prostheses require less energy. However, this can be offset by how a device assists the user in other ways. For example, a fixed ankle system may be quite light but its failure to adjust the foot/ankle position for ramps or stairs will cause the user to exert more energy to compensate.

The maximum user weight for the Kinnex is 125 kilograms.

K-Level Rating

Kinnex is intended for low-to-moderate-impact K3 use. It is not intended for high-impact sports, such as running, basketball, etc.

For a thorough understanding of K-levels, please see the Amputee Coalition’s web page on this topic.

User Software

Kinnex comes with a user application called the Kinnex App, which is available for download from either the Apple App Store (IOS device) or the Google Play Store (Android).

The app:

  • Displays product information, battery status, and a step count.
  • Allows the user to add, remove, and select shoe settings.
  • Lets the user adjust stiffness settings for the heel, ankle, and toe on a per shoe basis.
  • Allows the user to engage the Manual Lock mode, effectively turning the Kinnex into a fixed ankle system.
Kinnex Mobile App

With the release of Proteor’s Freedom Quattro bionic knee, we noticed that its mobile app, called the “Freedom Innovations App”, can also be used to manage the Kinnex, so it may be that Proteor is moving toward a universal app for its Freedom line of bionic devices. We’ll update this section as soon as we know more.


The Kinnex comes with a three-year manufacturer warranty. This is the same as the warranty for Ottobock’s Empower and Blatchford’s Elan models. All other bionic ankles come with a two-year warranty.


According to our information from individual users, Kinnex sells for between $18,000 to $22,000 US inclusive of all prosthetist fees.

To see how the price of the Kinnex compares to its competitors, please see our Bionic Foot Price List.

Compatibility With Bionic Knees

We do not have any information on the compatibility of the Kinnex with specific bionic knees. Unlike other manufacturers, who almost always limit the compatibility of bionic knees and ankle/feet to their own line of products, Freedom Innovations did not enforce this rule in the warranty terms of at least some of its products, such as the Plie Knee. And it does not appear to us as if Kinnex’s new owner, Proteor USA, has changed any of the warranty terms as of October 2021.

Customer Reviews

Occasionally, we run across high-quality customer reviews that we think should be shared. Here are the reviews that we’ve found for the Kinnex:

User Feedback Survey & Results

Are you or have you previously been a Kinnex user? If so, please share your insights with others looking at the Kinnex as a possible prosthesis.



We do not yet have a sufficient number of survey participants to publish fair and accurate results for the Kinnex.

As soon as we do, we’ll update this section.

Considerations Before Buying a Kinnex Foot/Ankle

When Proteor first took over Freedom Innovations (the original creator of the Kinnex), we had some concerns about whether Proteor had a sufficient sales & support network in place to properly support its Freedom Innovations products.

We’re happy to report that those concerns have been addressed, as Proteor has made significant progress in improving its sales & support network, including its recent additions of:

  • insurance reimbursement support;
  • an official published policy on loaner knees during repair.

For a list of competitor devices, see All Bionic Feet.

For a complete description of all current lower-limb technologies, devices, and research, see our comprehensive guide.

For more information on the Kinnex please see this dedicated website.

Click here for more information on Proteor USA.

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