One human hand contains 27 bones, 34 muscles, and over 100 ligaments and tendons.
Together, our hands perform millions of fine movements that allow us to grasp and manipulate objects, interact with our environment and perform self-care activities. We use them when greeting someone, grooming and feeding ourselves, communicating with others − really the list can go on and on. Due to our high reliance on them, the loss of one or both hands by amputation could quickly become a very overwhelming experience. Thankfully, prosthetic hands are now more widely available than ever before, helping individuals with upper limb differences maintain function and independence.
The first known prosthetic hand was made in 77 AD in Rome, given to a Roman general for use on the battlefield. The hand was roughly described as “iron tied to his arm”. A more complex hand was developed in 1505, this time for a German Knight. Again, this hand was iron, however its more complex design featured five fingers that were passively movable. Since then, prosthetic hands have continued to evolve in complexity, usability, weight, and design. Below is a summary of some prosthetic hand categories that are currently widely available.
- The most rudimentary of available prosthetic hands are passive prosthetics. These silicone devices are chosen for cosmesis but often have little functional capabilities. They can, however, be highly customized for skin tone, texture, and even nail color.
- Another option is a body-powered prosthetic hand. These devices use a lever and pulley system, with a cable connecting the movable hand to an intact body part. When the user pulls on the cable, the hand will open or close. These are typically easy to use but offer only a single action that can limit object manipulation.
- A more complex option is a myoelectric prosthetic hand. These devices tend to be more expensive, but they allow multi-joint movement to complete higher-level tasks. Some specific examples of myoelectric hands are:
- i-Limb by Ossur: This hand has five individually powered digits, including a thumb capable of rotation. This hand offers varying grip strength, an increased in speed of movement, as well as an anti-drop feature.
- Bebionic by Ottobock: This hand has 13 pre-programmed grip options, including “mouse grip” for using a computer mouse, and “tripod grip” to grasp small objects such as coins.
In addition to those readily available, there are other hands currently in testing and development which show promising results so far.
- The LUKE/DEKA arm, which is being developed by the U.S. Department of Veterans Affairs is showing positive results. In clinical trials this hand is reportedly capable of real time, individual finger movements comparable to a human hand. It is advertised as “the first prosthetic arm capable of performing multiple simultaneous powered movements”. It is also noted to be user-friendly and intuitive, which may help improve user retention.
- The Cleveland Clinic is also developing a bionic arm which, according to their press release, “provides people with amputation a complete restoration of natural arm function.” This device is described as a neural-machine interface, connecting directly to the user’s nerves. This allows them to move the prosthesis in the same way they do with their other limbs, by thinking about it.
Engineering a device that can mimic the complexity of the human hand has proven to be a challenging task. Current devices have evolved over centuries to where we are today, and while there is ongoing research and development, those available now are still quite impressive. As mentioned earlier our hands are responsible for so many tasks, and each of those tasks requires thousands of small muscle movements with graded force and high precision. For those with upper limb loss or difference, each year of work that goes into this field can make huge differences in their quality of life.