An orthopaedic surgeon resident Andrew Pedtke, MD, and a prosthetist, Garrett Hurley, CPO (Certified Prosthetist and Orthotist), both working at the University of California San Francisco, discovered a mutual passion for both surfing and international health. The pair spent a good amount of time working together overseas to treat people with orthopaedic problems and to conduct research.

Fig. 1– Garrett Hurley makes adjustments to the Infinite Socket.

Their work abroad led them to work with a number of amputees. Hurley was always thinking of a sustainable prosthetic that could be manufactured easily. On one of their trips abroad, he came up with a novel concept for a dynamic and modular socket. Pedtke recalls that it made sense from his understanding of medical devices and the prosthetic industry. The more they discussed the possibilities in prosthetics, the more they realized there was an unmet need.

Inspiration Strikes

As a prosthetist, Hurley had seen the countless steps it takes to create a prosthetic socket for a patient. He had a vision on how to get rid of all the wasteful energy and time in the fabrication of the socket. Distal components of sockets are entirely interchangeable. People have running feet and knees, and even different components for their daily activities. He saw diversity in distal components, and began applying the concept to the socket. The fabrication process and ultimate fit are somewhat archaic, he realized. He decided to develop something modular and customizable. By deconstructing the existing socket and taking inspiration from how things are built on a modular platform for other components and in other industries, he came up with a new approach.

Once their basic concept took shape, the pair realized that they needed to bring in more experts in other fields. They recruited a materials scientist and an industrial designer. The traction from those two disciplines led to recruitment of a multidisciplinary team including a patent agent, fashion designer, 3D technology expert, prosthetists, and amputees. This diverse team brought a broad perspective to the development of a new type of prosthetic socket. (See Figure 1)

How It Works

Fig. 2 – A peek inside the novel prosthetic socket.

According to statistics, there are about 625,000 major limb amputees in the United States, with 75,000 new amputations performed each year. Historically, prosthetic sockets are a one-off mold of a person’s limb at a given time. Using plaster molds, prosthetists capture the shape of a limb, and then make a rigid system based off that mold. Much like any body part, an amputee’s residual limb is constantly changing. Traditional prosthetic sockets do not change with them.

The Infinite Socket is considered a first truly modular and customizable prosthetic socket. This socket not only gives the end-user adjustability with micro- and macro-tensioning systems, but it also empowers clinicians to be more efficient in fabrication and fitting of the socket. With a condensed fabrication time, the clinician can spend more time finding a proper fit and analyzing the end-users gait. If the residual limb changes, the user and prosthetist are both able to make necessary adjustments to accommodate the changes.

There are two core concepts behind the socket: modularity and adjustability. It is modular in the sense that it consists of a generic set of components. These components are pre-assembled, sized, and customized to a user based off a digital scan of their residual limb. Generic components eliminate one-off molds, while still capturing the customized fit for each user.

It is adjustable for both the user and the prosthetist. The user has two tensioning systems to account for volume loss. The macro-tensioning system is integrated into the brim and can account for large volume change (i.e., recent amputees experience large fluctuations in volume, particularly in the first six months). The micro-tensioning system allows the user to make adjustments on a daily basis and account for smaller volume change or activities. For example, sitting at an office chair might require a different fit than walking 10 blocks for lunch.

The prosthetist can heat thermoplastic materials in the brim, struts, and distal cup, to refit the socket if a user changes shape. The base-plate has channels up to 10mm of lateral movement or 40 degrees of rotation. There is a telescoping mechanism in the ischial seat to move the seat just below the ischium. There are also various models of the ischial seat, with different designs to accommodate different shapes. (See Figure 2)

Fig. 3 – Hurley works with an amputee fitting the new socket.

Much like the c-leg (a microprocessor knee unit) provides stability and stance control for users, this technology provides comfort and adjustability. Comfort and stability are two of the biggest deterrents for amputees to wear their prosthesis. The new socket empowers users to take control of their fit. The system allows for early mobilization, better long-term solutions, and an increase in overall comfort. If a user experiences volume change, they can make adjustments with the tensioning systems independently of their prosthetist. If the volume change becomes so severe that the prosthesis no longer fits properly, they can enlist their prosthetist to reshape the socket without needing to fabricate a new one. Its long-term benefits come from its ability to adjust with the users residual limb and give the user full control over their prosthesis. (See Figure 3)

Where It Stands Now

LIM Innovations, a San Francisco-based medical device startup company, was officially incorporated in October, 2012. It was spun out of a grass-roots goal to create better sockets for amputees, since the real need for prosthetics is improving socket technology and fabrication efforts.

The Infinite Socket has been on the market since September 4, 2014. The company has been in discussion with major medical centers, military groups, and prosthetic facilities across the country. Its studies have consisted of internal pilot trials with a variety of users and have expanded to limited clinical partnerships with plans to go beyond that in the near future to a full-market release. LIM intends to release a sport model, below-knee, and pediatric version, as well as accessories and other 3D printing concepts and technologies in orthopaedics. The company is currently working toward a Department of Defense grant and other forms of funding to help continue its efforts.

This article was written by Andrew Pedtke, MD, CEO and Cofounder, LIM Innovations, San Francisco, CA. For more information, Click Here .

Medical Design Briefs Magazine

This article first appeared in the February, 2015 issue of Medical Design Briefs Magazine.

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