Ossur’s Proprio Foot was originally launched in 2006 and was the first microprocessor foot/ankle system on the market. It has since been updated multiple times and includes many of the advanced features found in other foot/ankle systems. However, it uses an inter-step ankle accommodation strategy, which some view as inferior to the within-step strategies used by other microprocessor foot/ankle systems.
A Quick Look at the Proprio Foot
The following video is a commercial, so it is not ideal as an introductory testimonial. However, it does contain some lengthy sequences of Proprio Foot users walking on different types of terrain.
Given the potential small delays in ankle adjustment when using an inter-step accommodation strategy (which we explain below), we were surprised at the smooth gait demonstrated in this video over non-flat terrain. That having been said, it still does not appear to be as smooth as the gait exhibited by users of Freedom Innovation’s Kinnex or Blatchford’s Elan Foot. It is especially difficult to distinguish the gait of an Elan Foot user from natural movements.
Note, however, that our video observations are hardly conclusive, so we will continue to search for scientific studies that directly compare all available microprocessor foot/ankle systems.
Proprio Foot’s Key Features
Ankle Range of Motion (ROM)
The reported ankle ROM for the Proprio Foot is 16 degrees.
The foot component adds another 17 degrees, for a total ROM of 33 degrees.
The Proprio Foot uses an inter-step ankle accommodation strategy, which means that it only makes adjustments to the ankle when the foot is in the swing phase. Furthermore, it does not make these adjustments on each step, but instead requires multiple steps to adjust, depending on the terrain.
For example, the Proprio Foot requires 3 prosthetic steps before it adjusts the ankle to an 85 % match with the slope of a ramp. Adapting to stairs, both ascending and descending, occurs after the first prosthetic step. This means that the user has to take the necessary precautions on that first step.
To provide the user with extra toe clearance during the swing phase, the foot automatically provides four degrees of dorsiflexion after the first two prosthetic steps. This occurs on even surfaces, ramps, and stair ascent, but not on stair descent.
Note that some of these automatic adjustments do not occur at slow walking speeds.
Speaking of walking speeds or, more accurately, gait speed and cadence, the Proprio Foot will calibrate itself to the user’s natural gait, but requires a 15-step sample to do so.
Finally, the Proprio Foot will automatically detect when the user is pedaling a bicycle and set the foot in a neutral position.
Electric Power for Push-Off
The Proprio Foot does not use electric power to augment push-off at the end of the stance phase, but it does optimize energy storage and reuse through its carbon fiber foot.
The only microprocessor foot/ankle currently on the market that enhances push-off with electric power is Ottobock’s Empower model.
Proprio Foot’s Sensor and Microprocessor Capabilities
Ossur does not publish details of the Proprio Foot’s sensors and microprocessor(s) to the general public.
What we do know is that the Proprio Foot only attempts to automatically adjust the angle of dorsiflexion and plantar flexion. Since the Proprio Foot does not use hydraulics, there is no attempt to actively manage flexion resistance. However, the foot component used with Proprio does use a mechanical blade system to generate resistance during the stance phase, so the issue is not being neglected
Benefits of the Microprocessor System
Normally, this section is much longer, but, in this case, we can be quite succinct. The primary advantages of the Proprio Foot’s microprocessor system are:
- the ability to set its default ankle alignment based on a 15-step sample;
- the ability to automatically adjust the angle of the ankle to match stair or slope requirements;
- increased toe clearance during the swing phase;
The Proprio Foot’s battery life is 18 to 36 hours, depending on usage.
Water Proofing and Dust Resistance
The Proprio Foot is listed as an IP34 device. This means that it is protected against water splashes and solid foreign objects of 2.5 mm in diameter and greater. This is among the weakest IP ratings of all microprocessor feet.
According to our independent data from August, 2018, the Proprio Foot weighs 1,428 grams, but as much as 1,600 grams at its largest foot size.
This is comparable to the other microprocessor foot/ankle systems with the exception of Blatchford’s Elan Foot, at 1,200 grams, and Fillauer’s Raize, at only 749 grams.
User Weight Limit
The maximum user weight for the Proprio Foot is 125 kilograms.
Ossur describes the Proprio Foot as being suitable for “low to moderately active amputees”. Note, however, that Medicare requires users to have a K3 or higher rating for reimbursement for this type of device.
In any event, the Proprio Foot 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.
Ossur comes with a user application called the Ossur Logic App, which is available for IOS and Android devices.
The app allows users to:
- Set the default ankle alignment based on 15-step sample;
- Automatically align the ankle for shoes with different heel heights, or to make manual tweaks to those alignments;
- Adjust stair and ramp adaptation levels;
- Turn off or on various modes;
The Propio Foot offers a two-year manufacturer warranty, matching the Fillauer Raize Foot but less than the three-year warranty offered by Freedom Innovation’s Kinnex, Blatchford’s Elan Foot, and Ottobock’s Empower Ankle and Meridium Foot models.
According to our information from individual users, the Proprio Foot sells for between $20,000 to $25,000 US inclusive of all prosthetist fees.
To see how the price of the Proprio compares to its competitors, please see our Bionic Foot Price List.
Considerations Before Buying a Proprio Foot
To be perfectly honest, we think the Proprio Foot offers inferior technology when compared to Freedom Innovation’s Kinnex or Blatchford’s Elan Foot. But our opinion matters very little. What we really need (collectively) is an objective scientific study comparing the advantages and disadvantages of every microprocessor foot/ankle system on the market.
Short of that, we do strongly suggest that prospective customers at least test the Kinnex and the Elan Foot before purchasing the Proprio Foot.
If anyone disagrees with these statements, we’d love to hear from you!
For more information on lower limb bionics, see Understanding Bionic Legs & Feet.
Click here for more information on Ossur.