Meet LIM, the tech company creating the ultimate wearable: prosthetic sockets

It’s difficult for people who don’t have to wear a prosthetic leg to understand the potential impact of such a device. Some parts of lower-limb prostheses — like cheetah blade legs or microprocessor-controlled knees — are more recognizable, both because they’re more visible to others and because the bulk of innovation in prosthetics has been devoted to these parts in recent years. The socket is the unsung hero of the prosthetic system. Physically, it’s a giant cup that suctions onto a residual limb and attaches to the prosthetic. Conceptually, it is the critical interface between man and the machine.

For decades, sockets have been made pretty much the same way: the patient sees a prosthetist, a plaster mold is made, and a couple weeks later the patient goes back to try on the sturdy carbon fiber socket that has been produced. Sometimes, tweaks are needed, which could mean going back to the prosthetist and starting from scratch. Other times, the socket fits well — that is, until the patient loses or gains weight, which the LIM guys refer to as a "volume change." In that case, the socket can be uncomfortable or even painful for the wearer. And then it’s back to the plaster drawing board again.

That’s where LIM is different. Prosthetist Garrett Hurley and his co-founder, orthopedic surgeon Andrew Pedtke, first conceived of the LIM "Infinite Socket" in 2011 and started shipping the product in 2014. Unlike traditional sockets, LIM’s sockets are covered in soft material and are modular — more like a multi-part knee brace than a stiff carbon fiber cup. Some of LIM’s sockets can be created from just two scans and half-dozen measurements of a person’s residual limb; only one of their sockets requires making a plaster mold. In some cases they can ship a socket within 24 to 48 hours.

Some, though not all, of the 50 parts of the sockets are 3D-printed in house. The company, which rents a portion of its San Francisco workspace from a 35-year-old prosthetics and orthotics company next door, has buckets of these parts stashed in what it calls a "Limventory" room, where it can quickly swap out parts to repair or adjust a socket.

LIM isn’t the only group looking to advance prosthetic sockets. A Colorado-based company called Click Medical has created a solution that marries traditional socket materials (carbon fiber) with a Boa closure system (think ski boots) to create an adjustable socket. Another company, Benevolent Technologies for Health, or BeTH for short, is looking closely at the shape-shifting properties of the inserts that go into the sockets — so, not changing the socket itself, but the array of materials within it.

"If you look at the R&D of prostheses, companies have invested heavily in feet and knees and ankles," BeTH co-founder and chief executive Jason Hill said in an interview. "But a lot of advancements don’t reach a significant portion of the amputee population… if you take the 1.5 million amputees in the US, you have to look at the percentage of people who are actually going to get the most advanced technology, versus those who just need anything that can help them walk."

LIM’s primary aim with its high-tech socket is to create a more comfortable fit for lower-limb amputees, so that an amputee can wear it for longer periods of time and, hopefully, not even think about it. But because of its modularity and adjustability, LIM also hopes it will be a more cost-effective solution. Rather than remaking a new socket from scratch every time the wearer loses or gains weight — or even if the socket needs to be repaired — LIM could simply adjust the existing socket. "The overall goal is to help liberate a person from dependency on the health-care system, so they can function normally," LIM co-founder Andrew Pedtke said.

The sockets have been distributed to about 220 amputees to date, many of whom lost their limbs to disease and accidents. LIM also told The Verge exclusively that it has conducted pilot trials with the Walter Reed National Military Medical Center and Headley Court, the UK’s military rehab center, getting sockets to more than a dozen different amputees who lost their lower limbs during military service. (A spokesperson for the UK Ministry of Defense confirmed that the prosthetics department had purchased a few of LIM’s sockets for a limited trial; the Walter Reed National Military Medical Center did not respond to requests for information about the pilot trials.)

So how much does a LIM socket actually cost? Co-founders Hurley and Pedtke were hesitant to attach a number to an Infinite Socket when asked repeatedly about price. They pointed out that most sockets are sold to prosthetists, not directly to consumers.

The short answer, in terms of upfront costs, is that LIM’s sockets are no different than traditional suction sockets. Generally speaking, Pedtke said, the total cost of service for a socket will be billed to an insurance company or Medicare at $10,000 for an above-the-knee amputee, and $7,000 for a below-the-knee amputee, on average.

But LIM believes its approach could impact the cost of the care that is needed over time. And it’s a timely issue: last fall Medicare began proposing changes around coverage of prostheses, citing concerns of a bloated cost structure fueled by overprescription and fraudulent billing. LIM also plans to eventually make its sockets Wi-Fi-connected, so that a patient would have the option of sharing more data around socket abandonment, or how frequently the person falls, or even how long it takes him or her to put on the socket when getting up to go to the bathroom in the middle of the night.

One LIM socket wearer, San Francisco-based Robert Spotswood, said that he was "discouraged" by the look and feel of the traditional sockets he had to wear after he lost his leg in a car accident at age 16. The experience was especially trying because he was still growing, which means he went through three to four different sockets in his first year as an amputee.

"it was like trying to walk on your knuckles"

"It was painful. It was like trying to walk on your knuckles," Spotswood said in an interview with The Verge.

Spotswood, now 34, said the LIM Infinite Socket he wears now is similar to a "pair of tennis shoes. You can tighten your shoe or loosen your shoe. It’s a pretty simple concept." He rock climbs, can play a full round of golf as opposed to just nine holes, and says he doesn’t have to structure his dating life around "how far the bar is from the restaurant. I don’t think about it anymore." (Spotswood liked his LIM socket so much that he began helping the company with product design and business development, in exchange for shares in the startup.)

But despite its flexibility, LIM won’t work for everyone. Dan Berschinski lost both of his legs in 2009, while serving as an Army infantry platoon leader in Afghanistan. Since then he has gone through about 10 above-the-knee sockets, and 15 to 20 hip sockets. He tried wearing a LIM socket. It didn’t do it for him.

berschinski, a double amputee, still prefers traditional sockets

His biggest complaint was that the LIM socket was bulky. "I tend to wear shorts unless I’m going to a wedding or business meeting," says Berschinski, who has since gone on to get an MBA from Stanford University and has co-founded a plastics business with a friend. He also says that he doesn’t fluctuate much in weight. If he does get a new socket made, it’s covered through the VA. "My sockets are pretty darn good," he says.

And, as far as prosthetic advancements go, Berschinski is looking beyond sockets at the possibility of osseointegration, a process in which a titanium implant is permanently inserted into the bone of the residual limb.

But until that becomes a more viable option, he is in support of companies like LIM that are trying to improve the socket experience. "I want them to continue to pursue it," Berschinski says.

Pedtke and Hurley certainly have no plans to stop now. They are currently seeking venture capital funding to keep the business going. During the reporting of this story, the Infinite Socket was approved for Medicare coverage, and LIM says the just finished fitting another round of veterans in the UK.

"If people can ultimately manage their disability and / or limb health at home," Pedtke says, "well, you’ve just addressed a public health issue."

Additional reporting by James Temple

Photography by Vjeran Pavic

Video directed and edited by Vjeran Pavic and James Temple; script and narration by James Temple; additional reporting by Lauren Goode.