Nearly 2/3 of upper limb amputations involve finger or partial hand loss. Ossur’s i-Digits line of products provides one of the few bionic options to meet this need. Based on i-Limb technology, i-Digits offers myoelectric control over anywhere from 1 to 5 bionic digits (each device is custom configured based on the user’s residual hand).
A Quick Look at i-Digits
This video provides a look at using the i-Digits Quantum for daily activities.
It is easy to imagine millions of people around the world benefiting from a device like this…if only we could make it more affordable!
i-Digits comes in two models: Access and Quantum. Access is the basic model, while Quantum adds additional grip capabilities, as well as increased speed and strength.
i-Digits Key Features
Grip Patterns & Control System
i-Digits Access offers 12 different preprogrammed grips. The Quantum model offers 20 preprogrammed grips. This sounds like a big difference but most users only use a few core grips.
The main control advantages that Quantum has over Access are:
- the ability to create up to 12 custom grip configurations, which allows users to create custom grips for specific tasks;
- the ability to switch to specific grips using gesture control, meaning you can assign one grip to each of four prosthesis movements (forward, back, left, right); in the absence of this feature, users have to rotate through grips using other gestures, or choose a specific grip in a mobile app that communicates with i-Digits via Bluetooth;
- the ability to automatically switch between grips using grip chips; these are small Bluetooth chips that you can position around your environment that trigger specific grips when your i-Digits Quantum passes within a certain proximity; for example, you can place a grip chip near your computer to automatically switch to an ideal grip for typing on a keyboard;
- an increase in the closing speed of the digits by as much as 30%;
Here is a short video demonstrating these advantages:
Manually Positioned Thumb
Unlike its i-Limb cousin, i-Digits does not offer an electronically positioned thumb, if a thumb is present at all. Instead, users must manually rotate the thumb into the desired position.
This is not a major drawback. Myoelectric hands typically require some form of preparation before performing a task, such as selecting an appropriate grip. In most instances, users will intuitively rotate the thumb into position with their free hand.
The use of a manually positioned thumb is also a byproduct of i-Digits modular design, where each digit must be an individual unit. An electronically rotating thumb requires an additional actuator and stronger motor — both difficult challenges for a thumb that may or may not be present.
Automatic Finger Stalling
Similar to the i-Limb, each i-Digits digit will automatically stall out as it meets resistance, while the other digits continue to close. This ensures a natural grip for any object regardless of its shape.
The importance of this feature can be appreciated simply by observing how a natural hand grips an irregular-shaped object like a wine glass. Anything short of automatic finger stalling might result in an unstable grip.
In cases where a stronger grip is required, i-Digits Quantum offers a vari-grip feature. This allows the user to increase the grip force by sustaining a close signal. A perfect use case for this might be gripping a jar tightly enough to open its lid.
Sometimes, users of bionic hands can drop an object by accidentally triggering an open signal. i-Digits Quantum detects short, unintended open signals and compensates by re-closing the fingers.
Lift Capacity & Grip Strength
The maximum finger carry load for i-Digits is five kilograms. The maximum carry load for the overall device is 20 kg.
We do not have any information on grip force (i.e. no newtons rating), which is likely difficult to calculate given all the possible configurations.
Quantum is described as having up to 30% more strength than Access, but Ossur’s literature doesn’t define what this means.
We have not identified any complaints about durability with i-Digits. This may be because we have not been able to find many independent third-party reviews in general.
Ossur states that i-Digits has an expected service life of five years. They also recommend servicing the device once every 12 months, including replacing the batteries.
Note, i-Digits is not designed for use in water or other liquids, or for exposure to excessive moisture, dust, vibration, shock, or high temperature. As demonstrated in the introductory video of this article, users must take considerable care to protect the device.
We have not been able to obtain any reliable pricing information on i-Digits. This is partly because Ossur is incredibly secretive about prices for all its bionic devices, and partly because i-Digits can have many different configurations, so there is no one price.
However, based on the price of the i-Limb (estimated from $45,000 to $70,000 USD, depending on the model), i-Digits is likely expensive.
Considerations Before Buying the i-Digits
The biggest single consideration before buying any bionic partial hand is your prosthetist. This is because the natural residual of every partial hand can vary significantly. Bionic partial hands must therefore be extensively customized to match your specific requirements. This is true of every prosthesis, of course. It’s just that partial hands tend to have more possible configurations.
We therefore strongly recommend that you deal only with a prosthetist who has proven experience with partial hand devices.
Unfortunately, if you want a bionic partial hand, your product choices are limited. i-Digits is currently one of only two options that we know about. The other is the Vincent Partial 3, which appears to have similar functionality. But Vincent has not produced any English-language material or videos in years, which makes us question their commitment to the North American market.
One other option, which we’re currently researching, is a non-bionic alternative from Point Designs. This is a ratcheting device that appears to be extremely useful for a high percentage of partial-hand use-cases. One appeal of this type of device is a much lower cost; the other is exceptional durability. We hope to have a full article on Point Designs’ device by the end of September 2020.
For more information on upper limb bionics, see Understanding Bionic Arms & Hands.
For a list of competitor devices, see All Partial Hand Options.
Also, do not miss our article on Myoelectric Control Systems. Getting this part of your bionic system right is probably the single most important element in your long-term satisfaction.
Click here for more information on Ossur Prosthetic Hands and Partial Hands.