Introduced in 1997, with more than 75,000 fittings worldwide, the C-Leg is a proven bionic knee with excellent stability and dependability. At between $40,000 and $50,000 US for a complete solution, it is in the middle tier of pricing for bionic knees.
A Quick Look at the C-Leg
Starting at the 0:21 mark, the following video provides a good first look at the C-Leg tackling stairs and some challenging grass slopes:
This next video shows a user traversing typical man-made surfaces 12-months after using his C-Leg for the first time. What’s interesting about this video is that the user had been using crutches for 35 years since losing his right leg to cancer at age 15. He also had to undergo bone lengthening and osseointegration surgeries before he could use a prosthesis. So, while there is still a bit of stiffness in his gait, it is remarkable that he has achieved so much in such little time:
C-Leg Key Features
To understand how bionic knees work in general, please see Understanding Bionic Legs & Feet.
The short story is that the microprocessors in bionic knees have three main functions:
- automatically adjusting the resistance in the knee to ensure the proper level of support through each stage of the Stance Phase;
- 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 C-Leg performs these tasks by evaluating its sensor data 100 times per second and regulating the knee’s hydraulics in real-time. This allows the C-Leg to quickly adapt to changing terrain or changes in gait and/or walking speed.
Although the following video is for a slightly older version of the C-Leg (2014), it does an excellent job of explaining the design concept:
In addition to automatically managing the different phases/stages of the gait cycle, the C-Leg offers three other key features:
- an Intuitive Stance mode where the knee detects that the user is standing and automatically dampens the knee in a flexed position to provide maximum stability even on sloped terrains;
- a sitting mode where the knee automatically switches to free-swing when the user sits down, allowing the leg/foot to naturally settle into a relaxed position as well shifting the device into a battery saving mode;
- different user modes to optimize settings for special activities such as biking, golfing, etc.; users can switch between these modes using special motion patterns or Ottobock’s Cockpit application (see subsection further down);
Benefits of the Microprocessor System
The biggest benefit of the C-Leg’s sensor and microprocessor system is stability and dependability. According to clinical studies, the C-Leg reduces the frequency of falls by 64%. Also, 90% of users feel demonstrably safer with the C-Leg vs a mechanical knee. Significant improvements in walking speed have also been reported across all terrains.
Although these achievements are not as sexy as some of the more exotic features of the C-Leg’s sister product — the Genium X3 — their impact on the user’s quality of life cannot be overstated. Having a stable, dependable, more efficient bionic knee alleviates the need for the user to constantly manage his/her prosthesis. This greatly reduces the mental and physical energy required to walk.
The following is a promotional video from 2014 but it does a good job of summarizing these benefits from a user’s perspective:
Compatibility with Prosthetic Feet
To make life even easier, Ottobock’s Quickchange adapter allows you to switch prosthetic feet in seconds, much as you would change a pair of shoes.
The C-Leg’s battery can last for 40-45 hours, though Ottobock recommends charging the battery daily.
If completely drained, a full charge requires five hours.
Water Proofing and Dust Resistance
The C-Leg has an IP rating of 67, meaning it is fully submersible in fresh water up to 1 meter for as long as 30 minutes. It is also considered weatherproof, so it can be used when walking in the rain.
However, unlike its sister product, the Genium X3, the C-Leg is not designed to be routinely submerged or used in chlorinated pools or salt water. It is also not designed for use in the shower.
The C-Leg is dust resistant.
Device Weight & User Weight Limit
The C-Leg weighs 1.24 kilograms. The maximum allowable user weight for the knee is 136 kilograms.
The C-Leg is rated primarily for K3 use but it can also be used with high-end K2 and low-end K4 amputees. For a thorough understanding of K-levels, please see the Amputee Coalition’s web page on this topic.
The main use-case for the C-Leg is walking. While it can be used for biking, golfing, and even light running (with the right socket/foot), it is not designed for more extreme sports activities.
Ottobock provides a software application for users to manage some of C-Leg’s settings. The app is called Cockpit:
This app allows users to:
- Switch modes for different activities.
- Change settings for individual modes.
- Turn Bluetooth on and off.
- View the percentage of remaining battery charge, as well as the daily and total step counts.
Ottobock offers a full three-year warranty on the C-Leg including any repair costs due to defects, as well as a free service unit during repair and/or inspection. The C-Leg does not require fixed service inspections, so inspections typically occur only in response to a problem.
The warranty can be extended to six years at the user’s option.
According to our information, the C-Leg sells for between $40,000 and $50,000 US including the socket, prosthetic foot, and all prosthetist fees.
Considerations Before Buying a C-Leg
Because human bionics is still in its infancy, it is rare to be able to describe a bionic device as tried and tested but that exactly describes the C-Leg. Now in its fourth generation, it is the most studied, most widely used bionic knee in the world.
To be clear, it is not the most technologically advanced knee. That title currently belongs to the Genium X3 at more than 2x the C-Leg’s price. But if your primary use-case is walking and you are looking for an advanced, dependable knee with a proven record of increased stability and reduced stumbles/falls, the C-Leg deserves your consideration.
For more information on lower-limb bionics, see Understanding Bionic Legs & Feet.
Click here for more information on Ottobock.