Freedom Innovation’s Kinnex is one of the most advanced microprocessor ankle/foot devices on the market. With a 30-degree range of motion, 3 sensors, and a sophisticated microprocessor, Kinnex automatically adjusts to changing terrain on each step. Rated as an IP67 device, it is both dust resistant and fully submersible in water, allowing the wearer to brave the outdoor elements without concern.
A Quick Look at Kinnex
We prefer using independent videos to demonstrate the real-life functions of bionic devices. However, Freedom Innovations has released two short videos that give us close looks at Kinnex 2.0 handling some demanding tasks:
For those of us looking forward to the day when technology eliminates all disabilities, the ease with which Kinnex users perform these tasks is pretty inspiring.
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 ankle/foot 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.
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 recognize the slope before adjusting accordingly.
Electric Power for Push-Off
Kinnex does not provide any electric power to the ankle/foot to assist with push-off, but it does optimize energy storage and reuse through its carbon fiber foot plate.
The only microprocessor ankle/foot currently on the market that provides electric power to assist with push-off is Ottobock’s Empower model.
Kinnex’s 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 ankle/foot 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 shoes.
Benefits of the Microprocessor System
On even ground, Kinnex automatically adjusts the ankle’s dorsiflexion, plantar flexion, and ankle stiffness to mimic the motion of a natural ankle/foot. 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’s automatic adjustments eliminate the need for this unnatural compensation.
As shown in this next video, the ability to automatically adjust the angle of the ankle/foot 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 microprocessor 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 Proofing and Dust Resistance
Kinnex is rated as an IP67 device, meaning that you can submerse it in water for up to 30 minutes. It is also highly dust resistant.
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 ankle/foot position for ramps or stairs will cause the user to exert more energy to compensate.
User Weight Limit
The maximum user weight for the Kinnex is 125 kilograms.
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.
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).
- 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.
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 microprocessor 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.
Considerations Before Buying a Kinnex Microprocessor Ankle/Foot
It is difficult for us to provide much guidance on the Kinnex at this point, mainly because we lack reviews from users who do not have a relationship with Freedom Innovations.
There was a pilot study conducted in 2014 on the Comparative Effectiveness of Microprocessor Controlled and Carbon Fiber Energy Storing and Returning Prosthetic Feet in Persons with Unilateral Transtibial Amputation. This study used a Kinnex 1.0 device versus a fixed ankle prosthesis. But the preceding link is to a preliminary abstract only, as each user must pay to see the full study.
Otherwise, we cannot find any articles comparing the performance of Kinnex to any of its direct competitors. Nor can we find any independent video reviews.
The Kinnex App does receive excellent ratings on both Apples App Store and Google Play, but the combined number of reviews is less than 10.
In the absence of such information, all we can do for now is continue to monitor the internet for any mention of Kinnex, and then return to update this article as soon as we find something of value.
For more information on lower limb bionics, see Understanding Bionic Legs & Feet.
Click here for more information on Freedom Innovations.