There are over 57 million people worldwide living with trauma-related limb loss, yet these amputations make up only 22% of the amputee demographic in the United States [1-2]. Since the Covid-19 pandemic, amputation rates have risen significantly due to the formation of dangerous blood clots, making the need for a prosthetic device more prevalent than ever [3]. It is currently estimated that one in every 190 Americans is an amputee [4]. Despite the growing need for prosthetic limbs worldwide, nearly one-third of lower limb prosthetic users with reject their prosthetic device due to extreme discomfort and another 20% will experience reamputation from pressure ulcer due to a poorly fitted socket due to volume loss [5].
The importance of socket fit is not only imperative to keep the prosthetic connected to the residual limb, but if the fit is flawed, then it can lead to complications such as redness, pressure ulcers, reduced regional blood flow, sores, tissue death, gangrene, and even complications as extreme as reamputation [6-7]. Understanding the residual limb-to-prosthetic socket interface is essential for creating a near-perfect fit that reduces tissue damage and incidences such as the ones listed above [7].
In the 80 days post-amputation, residual limb volume decreases by over 9% and does not begin to level out until nearly 160 days after amputation [8]. Because of this, amputees generally do not fit with a prosthetic limb until their residual limb volume remains steady, as the rigid socket is unable to account for these changes. This is ultimately detrimental to the amputee as studies have shown that early prosthetic fitting improves gait, increases independence, decreases maturation time, increases physical activity, and increases adaptation of definitive sockets [8]. Once fit for a definitive socket, the residual limb will continue to change in volume depending on the time of day, activity, temperature, weight loss, weight gain, salt intake, and numerous other biological and environmental factors.
An amputee must constantly adjust the volume of their socket, by adding or removing prosthetic socks, to maintain proper fit and decrease complications. However, many amputees don't know when or how to do this or find it inconvenient to do so [6]. Ultimately, sockets today are unable to adjust for the daily volume fluctuations of the residual limb and it is vital to account for volume changes for the health of the limb and the well-being of the patient.
Residual limb with 15 ply prosthetic sock to full volume loss [9].
Prosthetic socks are specialized socks designed to improve comfort and reduce the risk of skin irritation and pressure sores when using a prosthetic limb. They are the most common socket volume modification technique, as they are easily accessed and allow for the patient to determine socket fit though the varying the sock thickness and size. However, prosthetic socks have limitations as they cannot account for local volume change, which can cause pressure in sensitive areas. Additionally, patients with poor proprioception may restrict their blood flow when adding too many socks or not be aware of when they need to add socks, leading to discomfort or potential health risks.
The flexible inner prosthetic socket is designed to address increases in residual limb volume by providing a relief cut-out in the hard outer shell that is filled with a soft inner socket. It can accommodate changes in limb volume, reducing the need for frequent adjustments or additional socks. However, it can be costly and may not provide as much stability or control as a traditional socket. Additionally this solution is not viable for volume loss.
Socket with cut-out and flexible inner socket [10].
Revo-fit prosthetic socket with boa panel cabling [11].
The Revofit Boa Panel Cabling System uses a series of adjustable cables that are tightened using a Boa closure system, which can be adjusted to provide a customized fit that accommodates changes in limb volume over time. The primary benefit of the Revofit Boa Panel Cabling System is its adjustability, which can help to provide a more comfortable and secure fit for individuals with fluctuating limb volume. However, there are also some potential drawbacks to using the Revofit Boa Panel Cabling System. For example, if the cables are tightened too much, it can lead to discomfort or even restrict blood flow to the residual limb. Additionally, the system can be expensive and is not widely available.
The University of Washington's auto-adjusting prosthetic socket is an innovative technology designed to address the challenges of volume changes in the residual limb. The system uses sensors and an actuator to automatically adjust the fit of the socket in real-time, providing a more secure and comfortable fit. One of the primary benefits of the auto-adjusting prosthetic socket is its high adjustability, which allows for precise and immediate adjustments in response to changes in limb volume. This can help to reduce the need for frequent adjustments or additional prosthetic socks, improving overall comfort and quality of life for prosthetic users. While the technology is still in the testing phase, it shows promise for the next steps in prosthetic socket design. The ability to automatically adjust the fit of the socket in real-time has the potential to greatly improve the functionality and usability of prosthetic devices, allowing for more natural and intuitive movement.
University of Washingtons Auto-Adjusting piston socket [12].
The goal of our project is to develop a smart socket that changes its fit to provide a more comfortable experience for below knee amputees in response to volumetric changes. This can be broken into our top five goals: safety, comfort, ease of operation, durability, and reliability.
Made by Savanna Turner