Freedom Quattro Knee from Proteor

Quattro Knee Feature Image

The Freedom Quattro knee is the first new microprocessor knee in five years and features some important advancements.

What’s On This Page?

A Quick Look at the Quattro Knee

One of the reasons that we wait a few months before writing an article on a new bionic limb is that we prefer to use videos from actual users or independent reviewers, and it takes time for those to emerge.

Unfortunately, such videos have not yet materialized for the Quattro. What we have instead are two videos of an entirely different scope. The first video is essentially a short commercial that has very little educational value except for its references to a few key features:

  • Quattro’s support of up to 20 activity-specific modes, which means that it can adapt to different types of activities.
  • The ability to control the knee’s modes and settings from a user app. Again, what’s impressive is the degree to which Quattro has embraced this adaptability.
  • Quattro’s extended battery life, which is not only a convenience factor but can also bail users out of situations like forgetting to bring a charger on a weekend trip.

Here is the video in question:

On the opposite end of the spectrum, we have a video that is intended for prosthetists, so it includes a lot of information that may not be of interest to users. However, the section from 05:15 to 12:52 does a great job of summarizing the Quattro’s features for users at different activity levels:

We elaborate on these features in the sections below.

Quattro Knee Key Features

Sensor & Microprocessor Capabilities

To understand how bionic knees work in general, please see A Complete Guide to Bionic Legs & Feet.

The short story is that the microprocessors in bionic knees have three main 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 also the proper foot clearance during this phase, especially when ascending stairs, ramps, etc.;
  • assisting in stumble recovery.

The Quattro knee fulfills these tasks but with some notable improvements:

  • it captures data 250 times per second from 3 sensors;
  • it processes that data twice as fast as other microprocessor knees currently on the market;
  • it uses its increased data collection and processing capability to continuously adjust its hydraulic settings in response to the user’s movement, terrain, etc.;

The three sensors that make the Quattro’s continuous adjustments so effective are:

  • An angle sensor to detect the angle of knee flexion and how quickly that angle is changing;
  • A load and torque sensor, which measures the load on the knee and the direction from which the knee is being loaded;
  • An Inertial Measurement Unit (IMU) consisting of acceleration and orientation sensors that detect if the user is going backward or forward, down stairs/ramps, sitting, and also where the user is in the gait cycle.

According to the manufacturer, Proteor, all these features make the Quattro highly intuitive to use.

However, it is Quattro’s support of up to 20 different activity modes that we find particularly intriguing. Note, Quattro is not the first knee to offer different modes. Indeed, it has become increasingly popular among microprocessor knees to offer modes for common activities like walking, running, and bicycling. But Quattro’s support of up to 20 modes sets a whole new standard because modes can be created for things like skating, riding motorcycles, or even an alternative walking mode for when the user is feeling tired.

We’ll adopt a wait-and-see attitude toward this for now but it is certainly an exciting prospect!

Compatibility with Prosthetic Feet

The Quattro knee is compatible with many K3 feet on the market. Unlike with some bionic knees, using a foot made by someone other than the knee’s manufacturer does not invalidate Quattro’s warranty.

Specific recommendations for compatible prosthetic feet include:

High K3 users:

  • Rush Rogue 2
  • Freedom ShockWave

Moderate K3 users:

Low K3 users:

  • Kinterra foot/ankle
  • Freedom Highlander


The Quattro knee’s battery can last for 2 to 3 days depending on the level of activity. Its recharge time is 2 to 3 hours.

Users can also purchase a Booster Battery Kit that supports recharging the battery while in use but we do not yet have complete information on this option.

Water & Dust Resistance

The Quattro has an IP rating of 67, meaning that you can fully submerge it in fresh water up to 1 meter for as long as 30 minutes. However, Quattro cannot be used in the shower or in chlorinated or salt water.

The Quattro is considered dust-proof.

Device Weight & User Weight Limit

The Quattro knee weighs 1.65 kilograms. The maximum allowable user weight for the knee is 136 kilograms. Both of these numbers are in the upper range for microprocessor knees that do not offer power augmentation (e.g. Ossur’s Power Knee).

K-Level Rating

The Quattro is rated for all levels of K3 use.

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

User Software

The Quattro Knee offers a mobile user app called the “Freedom Innovations App”. This app is available for both iOS and Android devices. The app uses Bluetooth to find and connect to the knee.

At first glance, this app appears similar to the apps for many bionic knees, as it allows users to adjust basic settings:

Freedom Innovations App 02

However, as mentioned, the user can create up to 20 different activity modes for the Quattro, 18 of them fully programmable via this app.

As with many other bionic limb companies, Proteor also offers software for prosthetists for full setup and configuration. Users can also upload usage and cadence reports to their prosthetists to help them monitor progress and improve patient outcomes.


The Quattro comes with a 3-year warranty for manufacturing defects for the knee itself. There are no service requirements for this warranty.

Users can purchase an extended warranty for an additional 2 years of coverage.

The battery charger and accessories have a 12-month warranty.

In case of repair, a loaner knee is available upon request.


According to our information, the Quattro knee sells for between $30,000 and $40,000 US including the socket, prosthetic foot, and all prosthetist fees.

It can also be bundled with the Kinnex Foot/Ankle for around $50,000 US, though note that this is our estimate of the price for that combination. We do not yet have any verified user purchases at that price.

For a complete list of prices for other microprocessor knees, please see our Microprocessor Knee Price List.

Quattro Knee User Feedback Survey & Results

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



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

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

Considerations Before Buying a Quattro Knee

We do not yet have any independent, third-party assessments of the Quattro, mainly because it was only launched in September of 2021. Consequently, we have no official opinion of the knee.

However, we do note that the Quattro seems like the next logical step in the evolution of mainstream bionic knees, especially its advanced sensing and microprocessing capabilities, as well as its ability to support 20 specific activity modes. These improvements alone suggest that it is worth checking out.

We would also like to note that the manufacturer/distributor, Proteor (Proteor USA in the United States), 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.

Because of these improvements, we will now remove all our previous cautions about these issues from all our articles on Proteor’s bionic limbs.

For a list of competitive devices, see Current Options for Microprocessor Knees.

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

For more information on the Quattro knee, please see this dedicated website.

Click here for more information on Quattro’s manufacturer/distributor in the U.S, please see Proteor USA.