Prosthetics are usually used to help when someone loses a full or partial limb due to an accident or amputation. Artificial limbs are also prescribed for some people who cannot use an existing body part, which can occur following stroke or spinal injury. We’ve written about exiii’s HACKberry prosthetic hand and the OpenBionics project’s design for an anthropomorphic robot hand. Each of those open source projects support replacing missing or damaged hands. But what if prosthetics were used to add extra functionality rather than to replace a missing or nonfunctioning body part?

London-based Dani Clode Design has developed a self-descriptive prosthetic called  The Third Thumb. Built with 3D-printed parts, The Third Thumb adds the sixth digit to a human hand. The extra thumb is located in line after the fourth or pinky finger and serves as a second opposable digit. Structurally, The Third Thumb includes a flexible digit that is 3D-printed to match the hand and finger size of the recipient. The extra thumb is held in place by a brace that wraps around the palm and connects to a wristband. The wristband holds the motor used to articulate the thumb, a Bluetooth wireless component, and a battery. The relative force with which the prosthetic pushes against an object is directly controlled by pressure sensors on the bottom of a shoe or boot. The pressure data is transmitted to the wristband via a second Bluetooth component attached to the footwear.

Theoretically, we could be fitted with an extra thumb for each hand, the added digits much more useful than gaining extra fingers. Fingers can wrap around, point to or push, or squeeze to a limited degree but not work in opposition to other digits. Try picking something up with just a finger – unless there’s an adhesive involved, it won’t work. This project extends the concept of technology as a way to augment existing human abilities, and not just a way to replace or maintain normal functions.