Research Focus

“Prosthetic sockets today reflect 50 year-old technology. Conventional hard sockets do not accommodate volume changes, are quite expensive, and take weeks for fabrication. The iFIT prosthesis is an adjustable device that is fit in a single session with a few hand tools. This socket is particularly useful as either a preparatory device when the limb undergoes significant volume changes, or for persons with renal or heart disease who experience daily fluctuations in their limbs…” – Dr. Timothy Dillingham

Amputations and Prosthetics

For the past ten years, Timothy Dillingham, MD, MS, current Penn PM&R Chair, and collaborating engineer at iFIT Prosthetics Limited Liability Company (L.L.C.)*, and Advanced Design Concepts (ADC) Engineering, both firms based in Pewaukee, Wisconsin, have addressed the shortcomings with conventional prosthetic sockets by designing, prototyping and manufacturing adjustable prosthetic sockets—the iFIT System of Prostheses. The fabrication of conventional prosthetic sockets, encompassing casting, molding and shaping, can take months to complete. In contrast, the iFIT prostheses are injection-molded and mass-produced, resulting in strong, flexible, waterproof and well-aligned prosthetic sockets. These prostheses can be fit and aligned during a single outpatient or home visit. This results in early rehabilitation and gait training with more rapid reductions in residual limb swelling and enhancement of psychological well-being. A buckle system with safety locks allows the patient to re-adjust the socket fit whenever they wish. The adjustable transtibial socket is adjustable and extends over the knee in a supracondylar fashion for optimizing sensory feedback to support balance and gait stability. The adjustable transfemoral socket uses a sub-ischial (low profile) design, firmly grasping the soft tissues of the thigh to provide support without extending up into the ischial tuberosity area like conventional transfemoral sockets. Between 2011 and 2013, the Small Business Technology Transfer Program of the National Institutes of Health’s (NIH’s) National Center for Medical Rehabilitation Research within the National Institute of Child Health and Human Development funded the development, clinical testing, and commercialization of the transtibial iFIT prosthetic socket. Thereafter, between 2015 and 2020, the Small Business Technology and Commercial Readiness Programs within the NIH’s National Institute on Aging, further supported operationalization of the transtibial iFIT prosthesis, as well as the development of the transfemoral iFIT prosthetic socket, and exploration into pediatric applications of these prosthetic systems:

Penn PM&R’s Gait and Biomechanical Lab, directed by Dr. Dillingham and managed by Jessica Kenia, MS, is the clinical testing site for these devices. Different sizes of adjustable sockets were made to fit approximately 85% of persons with transtibial and transfemoral lower limb loss, accommodating patients weighing up to 350 pounds. A feasibility study by Dr. Dillingham’s research team (Dillingham, T., Kenia, J.J., Shofer, F., Marschalek, J. A prospective assessment of an adjustable, immediate fit, transtibial prosthesis. PM&R 2019;11:1210-1217) compared the use, satisfaction, safety, and ambulatory function of 26 transtibial amputees using iFIT prostheses with their conventional prostheses: patient-reported satisfaction was significantly higher, and anterior tibial and lateral intra-socket peak pressures were significantly lower using the iFIT system; gait biomechanics were comparable. No falls or limb ischemia were reported. This research team recently finished a study on transfemoral subjects using a similar pretest-posttest design. These adjustable sockets were rated overall as more comfortable, stable and easier to don and doff than conventional transfemoral prostheses in a group of 11 subjects. A surprising finding was that the compressibility of the thigh soft tissues was considerable: up to 10 centimeters of reduction in circumference was observed when the socket was comfortably closed around the thigh residual limb. This underscores why casting and three-dimensional limb imaging often results in poorly fitting sockets in that these methods of fabrication do not accurately estimate soft tissue compressibility.

…”we are profoundly grateful for NIH’s funding to develop these adjustable sockets…it is our sincere hope that these devices will provide greater function and comfort for people with lower limb loss, while increasing access to high quality prosthetics at affordable prices for patients and their families...” – Dr. Timothy Dillingham

The iFITsystem is designed to be a “prosthesis in a box” which can be shipped anywhere in the world including austere and resource-challenged environments, and successfully fit by any clinician after a modest level of training. This adjustable and mass-produced system can be applied in international situations in which amputees do not have ready-access to prosthetic resources to support functional mobility. Amputees in developing countries, particularly in rural areas, often are unable to attend school or work after limb loss because of limited mobility. Moreover, prosthetic services can be non-existent augmenting the challenges to support such individuals with limb loss. As a part of iFIT Prosthetics’ international mission, a relationship with a collaborating physical therapist, Bethany Wolf, PT, DPT, was developed. Since 2013, Dr. Wolf has served as the volunteer coordinator and assistant director of outpatient and home-based physical therapy, in affiliation with Friends of Redeemer United, based in rural Jamaica, and supported by the local catholic diocese and parishes there, as well as by the Drayer Physical Therapy Institute of Hershey, PA. Trained by Dr. Dillingham’s team, Dr. Wolf recently and successfully fit five persons with transtibial limb loss including the twelve-year old boy depicted in the photo above who had a congenital limb loss and who had previously walked with crutches. The iFIT system was fit and aligned during one visit. This young man walked out of the clinic with his prosthesis, and this prosthesis successfully accommodated his growth over the following year.

* Conflicts of Interest: Dr. Dillingham founded the company, iFIT Prosthetics, LLC, and is the major owner with financial interests in the iFIT prosthetic system. He signed a NIH compliant conflict of interest management agreement with the University of Pennsylvania Provost for Research. The opinions presented here do not necessarily reflect the views of the NIH; they are the views of Dr. Dillingham and his research team.