Improving Prosthetic Arms for Amputee: A Better Fit and More Functionality

Acceptance of prosthetic arms has long been a problem for clinical prosthetics, and recent studies indicate that recent advancements have done little to improve usage. Objections related to the fit and comfort of prosthetic arms remain the main reasons cited for the disuse of the devices, numbering nine of the top ten reasons cited for abandonment in a survey study. By addressing the literal point of pain for these users, the investigators hope to increase use and acceptance, allowing existing devices to have more positive impact on Veterans' lives. The breathability of composite sockets has been an acknowledged problem nearly since their development by the VA in the 1940s. Indeed, while the VA successfully developed a breathable composite socket very early on, it was quickly abandoned after it was discovered that the breathable composite recreated the problems with odor and cleanliness with leather sockets that the composites had been developed to solve. Industry leader Otto Bock discovered the same thing when it developed a porous silicone liner decades later. While VA and civilian providers were successful in replacing leather sockets with composites through the innovations in composites and other materials following World War II. Prosthetic clinics used to employ leatherworkers skilled in the art of making custom sockets and braces out of these traditional materials, but these services have disappeared along with the Veterans demanding them, and the workers capable of delivering them. By taking advantage of the benefits of the advanced materials and construction techniques that have replaced leather in the athletic shoe industry over the last seventy-five years, the investigators hope to restore much of the comfort and fit of these extinct socket designs, while at the same time delivering the improvements that have been delivered by the athletic shoe industry and advances in design and manufacturing over the same period. Lim design is working on a textile based prosthetic socket; however, the approach differs from the investigators': 1) The Lim design is not intended or currently suitable for upper limbs; 2) While a textile design, the Lim design cannot dynamically change in volume through the range of motion and constrains motion similar to any other socket once it has been adjusted; 3) The textile design of the Lim socket is nether breathable nor wicking and is designed to be used with silicone and/or gel liners, hence suffers from the same deficiencies with respect to heat and moisture management as traditional sockets. Lim Innovations and Ossur have publicly stated that they do not intend to pursue further innovations in the upper limb market. These frank admissions make it clear that the development of orphan devices for Veterans, must become the responsibility of the VA, whose goals for serving Veterans are sometimes in contrast with and not limited to the constraints of large and profitable markets. VA in collaboration with small companies can help fill this much needed void for innovation. VA has shown leadership in related domains with the research and design for ultralight wheelchairs, alternative controls for powered wheelchairs, and adaptive sports and recreation equipment, all of which eventually assisted the broader populations of Americans with disabilities. Harness discomfort is just as detrimental to acceptance as poor socket-body interface and can lead to contralateral damage to the axilla. Indeed, one recent study concluded that there was no acceptable level of force at which a body powered prosthesis could be operated pain and fatigue free with a traditional harness. While the conclusions of this study obviously contradict the staying power of the body powered prosthesis and harness system accepted by more than 90 per cent of the roughly half of users who accept a prosthesis at all, it does indicate that there is substantial improvement to be made in harnessing that could significantly improve both acceptance and comfort of the users who have been willing to tolerate the uncomfortable standard of care that has seen slow progress for decades.

Study Objectives and Hypothesis:

Specific Aim 1: Improve and develop the design and systems for fitting an innovative new transradial suspension design based on currently available technology used in athletic shoe construction.

• Design Criteria 1a: Optimize CAD documentation by revising and translating the current Autodesk Fusion 360 design to SolidWorks, aiding customization and improving design for manufacture.
• Design Criteria 1b: Verify that the currently Direct Metal Laser Sintered (DMLS) printed wrist and quick release can be efficiently and effectively CNC machined.
• Design Criteria 1c: Create fixturing and finalize CNC programming for manufacture, including the specification of manufacturing tolerances to ensure proper fit of components.
• Design Criteria 1e: Verify forearm and elbow counter parts-currently printed in Multijet Fusion (MJF)-in Selective Laser Sintering (SLS) or Fused Deposition or Fused Filament (FDM/FFF) Nylon material.
• Design Criteria 1f: Automate adaptation of the design through plugin and API development.
• Design Criteria 1g: Optimize production of 2D textile patterns with, for example, ExactFlat.
• Design Criteria 1h: Design a digital or Brannock-like fitting device for measuring the residual limb and locating bony prominences of the limb to inform the socket design.
• Design Criteria 1i: Design the device to weigh less than 2 pounds in total. The design will address common limitations of current upper-limb prostheses by improving comfort, range of motion, function, and sustained prosthesis use among individuals with transradial amputation.

Specific Aim 2: Verify performance gains for the innovative KSH system that can be delivered to Veterans. The new design is expected to significantly exceed the performance of the standard-of-care prosthesis in quantitative measures.

• Hypothesis 2a (H2a): That the improved KSH will provide a higher tensile static load bearing capacity before failure than the current standard-of-care prosthesis.
• Hypothesis 2b (H2b): That the improved KSH will provide greater tensile loads in a dynamic environment. The KSH system will allow users to perform better on a rowing ergometer 10-minute test before failure than the current standard-of-care prosthesis, as measured using strokes per minute, power in Watts, distance in meters, maximal force, and time before failure.
• Hypothesis 2c (H2c): The improved KSH will provide a greater range of motion in flexion/extension than the current standard-of-care prosthesis.
• Hypothesis 2d (H3d): Participants will require less time for donning/doffing the KSH than their current standard-of-care prosthesis.

Specific Aim 3: Verify functionality of the KSH system through testing with end-users.

• Hypothesis 3a (H3a): Participants will report high usability with setup and operation of the device (>80 on the System Usability Scale (SUS)).
• Hypothesis 3b (H3b): Participants will report significantly higher Socket Comfort Scores (SCS) with the KSH than their current standard-of-care prosthesis.
• Hypothesis 3c (H3c): Lower weight will correlate with greater user satisfaction, and the KSH will be statistically and clinically significantly lighter than participants' current devices.
• Hypothesis 3d (H3d): Participants will report that they would switch to the new design or have an additional prosthesis with the new design.
• Hypothesis 3e (H3e): Participants will report significantly higher Orthotics and Prosthetics User Survey (OPUS) scores with the KSH than their current standard-of-care prosthesis.

Relevance to Veterans: According to the DoD/VA Extremity Amputation Center of Excellence there were about 3,000 Veterans with transradial amputations enrolled for VA Healthcare in FY21, out of about 62,000 Veterans with limb amputations enrolled for VA healthcare. Veterans with arm amputations from Post-911 conflicts number just over 200, and because the total number of Veterans missing arms is demographically small, this very fact has severely limited innovation in the field of prosthetic arms. Those missing at least all five fingers of a hand are among the VA's most significantly disabled Veterans, rated at 80 per cent disabled alone for the loss of a dominant hand. Many arm amputees are eligible for Special Monthly Compensation as well as vehicle and housing modifications, reflecting the degree to which these Veterans' lives are impacted by the impairment. Indeed, even among the civilian population, arm amputation is rare enough to easily meet the FDA's medical orphan criteria of fewer than 200,000 patients, though the FDA's orphan drug law specifically excludes medical devices, and the FDA has a lower device threshold of 8,000 patients, further limiting innovation. The NIH's Genetic and Rare Diseases Information Center (GARD) lists limb absence as a rare birth condition but doesn't mention the same disability acquired by trauma or through other diseases, such as cancer, which is the second most common cause despite the small total number from all causes. While the subject design can be extended to other levels of amputation, this study will focus on transradial, or below elbow amputees. This population represents approximately seventy-five per cent of the VA population of Veterans with arm amputations, a subset that is also much more likely to successfully wear a prosthetic arm. Over 90% of these users choose body powered. The design could be extended to other Veteran populations, including people with lower-limb amputations and other levels of amputation, potentially increasing the benefit by offering the same benefits to those Veterans. By targeting the portion of an orphan population that is already more likely to use the device for which improvement is sought, and by targeting the concerns that are most likely to lead to abandonment, this research stands to increase acceptance and therefore access to activities of daily living, employment and recreation that can improve quality of life for some of the VA's most impaired patients. Success could then also be translated to larger populations with similar needs. The proposed design is intended to address more than half the total population of Veterans with upper limb amputations and could with additional research and development be designed in the future for other levels of amputation, including lower limb and myoelectric upper limb use.