New 'digit' design to help people who have lost fingers

Brand Sampson and Marty Frana of Rochester-based Limb Lab recently received a patent for the design of a new "universal digit" prosthetic.

Some prototypes of the "universal digit" sit by the most recent version made with black alumuninum near the patent that was issued to Limb Lab co-founders Brandon Sampson and Marty Frana.
Jeff Kiger / Post Bulletin
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ROCHESTER — Sometimes seeing a problem repeated over and over will inspire a solution.

In the summer of 2018, five clients from the region arrived at Rochester’s Limb Lab prosthetic clinic after accidentally cutting off their thumbs. The accidents all happened within a two-month period.

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Limb Lab’s team is known for starting all conversations with the trademark question, “What do you want to do?” The answers from these clients spotlighted a need in the industry.

These clients all wanted to be able to continue to work as they had before losing their thumbs. One is a rancher and another one delivers mail for the Post Office. Another client missing a thumb works on an assembly line for a manufacturer.

That meant Limb Lamb’s prosthetists needed to find adjustable “thumbs” for the clients to wear to allow them to pick up things as well as other actions.


“I started looking at existing products for these guys and there aren't many. There was actually only one feasible solution,” said Limb Lab Founder and Prosthetist Brandon Sampson.

That solution was a friction-based prosthetic with screws to tighten it into place.

“As soon as these big guys started grabbing something, it would move and let loose. So they would tighten the friction to hold it, but then you couldn't reposition it,” he said. “So it was useless and frustrating for these guys.”

Sampson talked through the problem with Limb Lab’s co-founder Marty Frana, who is the company’s CEO. Frana works on the business side of the operation.

Limb Lab co-founder Brandon Sampson sits by the patent that he and co-founder Marty Frana recently were issued for their innovative design of a "universal digit" for clients who have lost a finger.
Jeff Kiger / Post Bulletin

“I love bouncing ideas off of him (Frana), because he sees it from such a different perspective than I do. He's a farm boy from Iowa. I'm a farm boy from Minnesota. On a farm, you figure out how to solve problems with baling wire and duct tape,” said Sampson.

They determined a successful prosthetic would need a mechanism that locks into multiple different places easily and also rotates into different places. After discussing the plan with an engineer, some simple, 3D printed prototypes were created.

Sampson has a case full of parts from the experiment. Eventually, they settled on a design that actually can be used as a replacement for any finger.

A client can use another hand or their teeth to lock it in place. In addition to having a full range of normal motion for a finger, their creation can also lock backwards in a position no natural finger or thumb should go. That can provide a hook for another way to carry something.


The next step was to submit an application to the U.S. Patent and Trademark Office to patent the design of their “Universal Digit.” Sampson and Frana filed that permit on Aug. 6, 2018.

The pair received approval for their patent – their first – on April 26, 2022. They join a large crowd of Rochester area inventors with patents.

Sampson and his team weren’t idle while waiting for the patent approval. They had 100 of the digits machined using aluminum. He said 48 clients, some who worked with prosthetic clinics, are now using those early versions of the locking digit. The aluminum version of the digits cost about $750 each.

Limb Lab also started embedding the digit in silicone and painting them to make them less noticeable. The silicone “skins” are also customizable. A client who picks up small pieces on an assembly line has a skin with an additional ridge to provide sort of a “shovel” to make the process easier.

Now Sampson is talking to large prosthetic makers about incorporating the universal digit into their product lines.

“There's definitely a lot of interest, and that's the cool thing. It has worked 48 times,” he said.

The Limb Lab has many ideas for variations or related products. Other applications are in the pipeline at the patent office.

Meanwhile, Limb Lab continues to stay busy working with clients. Sampson and Frana founded the business in downtown Rochester in 2018 with a vision and three employees.


There are now 40 Limb Lab employees working in six locations in four states. The original Rochester lab has expanded twice. Working with Brian Childs, another Limb Lab partner and its chief growth officer, Sampson expects to open two more offices in 2022.

Jeff Kiger tracks business action in Rochester and southeastern Minnesota every day in "Heard on the Street." Send tips to or via Twitter to @whereskiger . You can call him at 507-285-7798.

Jeff Kiger writes a daily column, "Heard Around Rochester," in addition to writing articles about local businesses, Mayo Clinic, IBM, Hormel Foods, Crenlo and others. The opinions of my employer do not necessarily reflect my opinions. He has worked in Rochester for the Post Bulletin since 1999. Send tips to or via Twitter to @whereskiger . You can call him at 507-285-7798.
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