We could all soon have a third thumb. Don’t worry, this isn’t some strange post-fallout mutation that humans will soon stumble into, but an innovative new prosthetic being tested in the UK. Specifically, it's being trialled by a team led by University College London researchers, who have developed a robotic limb that attaches to the hand.

Prosthetics are often seen as a way to replace a limb, the ‘third thumb’ is intended as an extension of human ability, allowing users to better grip and hold objects. But do we actually need an extra thumb? Or is this more of a gimmick than a functional tool?

How does it work?

The third thumb is a surprisingly simple innovation. It’s a 3D-printed wearable, strapped onto the hand opposite your biological thumb, and controlled by a series of wireless sensors...in your feet.

“Using pressure sensors under the toes, and a wearable around the ankles, all of this connects to a sensor on the arm to control the thumb,” Dani Clode, the maker of the device, told BBC Science Focus.

“Pressure from the right toe pulls the thumb across the hand, the same with the left toe which pulls the thumb up towards the fingers. This pressure allows the thumb to pick up, hold and act as an extension of the hand.”

This, in theory, sounds great. But how hard is it to learn to control a completely new limb? Surprisingly, not very.

As outlined in a recently published study, the team behind the thumb took it to the annual Royal Society Summer Science Exhibition. Here they were able to test their new robotic limb on 596 participants. Each person was given up to a minute to try out the device, attempting two tasks in this time.

The first was to pick up pegs from a pegboard one at a time and place them in a basket, using just the thumb. Overall, 333 participants were able to complete this task.

The follow-up task involved using the thumb with the rest of the hand and moving five or six foam objects. In total, 246 participants were able to move these objects into the basket.

Across the exhibition, they found 98 per cent of participants could use the device immediately. Ability levels were varied, but there was no link between people with higher levels of perceived dexterity – musicians and carpenters, for example – and skill with the thumb.

More importantly, the thumb was usable by people of all tested groups across age, gender and background. Only four people were unable to use the device because it didn’t fit their hand or they were unable to control it with their feet.

Why do you need a third thumb anyway?

It's a good question to ask. After all, we’ve got this far with two and we’re doing pretty amazing as a civilisation… okay, we’re doing just fine. But what will another thumb do?

The world of motorised limbs is growing rapidly with the intention of helping humans complete difficult tasks with ease. The extra thumb can be used more trivially to carry more shopping bags, hold your phone for easy scrolling, or hold your food in place while you’re cutting it.

However, it's the more specialised areas where the thumb thrives. It gives musicians an extra limb, unlocking new abilities for guitarists, pianists and drummers alike. Manual labourers who are trying to solder or surgeons can hold more equipment while working or increase their dexterity. Even bartenders carrying more supplies could benefit.

A hand wearing the third thumb holds four limes using the thumb to do this — Credit: Dani Clode Design & The Plasticity Lab

“I don’t see this as a replacement for a limb. This is an extension of the body – and that is the design philosophy I take with these prosthetics. Assistive prosthetics are there to extend what you can do, and can be used by everyone,” says Clode.

However, while the product has been tested on many groups of people, it could be a long time until we see it brought to a larger audience.

“It is quite challenging bringing a product to the masses. But in the short term, we’re pivoting into patient scenarios. We’re currently looking at research with patients who have broken limbs,” says Clode.

“Considering how easy it has been for people to pick it up, we’re looking at it as an assist for people who have recently broken their hand, and then leading into groups of patients who have had strokes and then also kids.”

While the product is usable by anyone and can be used in areas ranging from a phone holder, to an extra beer-carrying finger, or even a tool for guitarists to get an extra note, its use for accessibility is its priority.

For now, there is no planned price or a timeline for when the product will be widely available. However, if it proves popular in further trials, it might not be long until we’re all wandering around with a cyborg third finger.

About our expert, Dani Clode

Dani Clode is the designer of 'The Third Thumb'. She has designed and created an array of prosthetics for both the arm and hand. Her work aims to extend the use of the human form.

Read more: