Prosthetic Sockets/Interfaces: The Next Frontier for Outcomes-Based Research

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The environment for prosthetics-driven research has seen momentum and an increase in funding opportunities over the past five years. Advancements in power feet and knees, and the utilization of 3D
printing have catapulted the industry into mainstream media.
Healthcare policy efforts have also arrived in full force, demanding
clear outcomes and metrics that correlate with cost expenditures.
In healthcare’s shift to fee-for-value reimbursement, the O&P
community is forced to justify the provision of prosthetic devices.

Despite all the advances in distal components, the prosthetic socket—the interface between the prosthesis and residual limb—has received little attention and represents one of the greatest technology gaps in O&P. Optimal socket function is the most important aspect to the success of the prosthesis as a whole.

Research must focus on improved socket design and technology, acquiring clinical data and subsequent analysis, and delineating the ideal clinical outcomes that determine clinical success. By improving research and outcome measures, we can reduce healthcare service gaps and justify expectations of sophisticated patients and healthcare payers.

There has been consistent development of distal components, yet development in prosthetic sockets has been limited. Distal components behave through more predictable engineering principles. Their effectiveness can be determined using gait analysis and step count metrics to measure patient outcomes.

However, the prosthetic socket is bound by an intimate interplay with the human body where subjective satisfaction reigns king. Current medical literature specifically demonstrates that socket fit and feelings of empowerment are important factors in whether a patient wears his or her prosthesis. The importance of comfortable, secure socket fit coupled with the difficulty of objectively measuring that outcome and the highly individualized performance of this part of the prosthetic system, in contrast to the more predictable results seen with distal components, skews the future development framework in prosthetics. Capturing successful patient outcomes is much more difficult with a custom-molded socket than with mechanically engineered distal components. This dichotomy makes it increasingly difficult to analyze the impact of the socket/interface on the use of the entire prosthetic system and its influence on subsequent health metrics, such as ambulation and daily function.

Outcomes are often defined by the several steps taken in the prosthetic clinic to demonstrate ideal gait or the clinician’s best attempt to get a snapshot of the patient’s function. Patient satisfaction and integration to life outside of the healthcare setting is often secondary to functional tests conducted in the clinic, lacking consensus on what is considered successful mobility and/or function, or simply cannot be fully measured. The lack of data in this area may have a direct impact on long-term health effects, including obesity, diabetes, and hypertension.

prostheses wearers at Golden Gate bridge

A well-fitting socket helps users to take advantage of the functionality of other components. Photographs courtesy of LIM Innovations.

If metrics of gait analysis and step count are used solely to define function, it leads to an incomplete and inaccurate picture. Furthermore, generic metrics such as comfort scores, rather than functional outcomes and end-user satisfaction, simply do not carry enough weight in the payer community to justify many provisions of care. It is important to note that there have been recent concerted efforts in the O&P industry to develop a set of outcome measures. Many researchers and clinicians would like to see changes in the way that O&P outcomes are developed, collected, and funded. Designing and implementing successful studies presents a series of challenges though. Currently, there are no universally agreed upon, valid, and reliable tools to capture and describe prosthetic sockets. LIM Innovations is seeking help from key opinion leaders, people with amputations, prosthetists, rehabilitation physicians, academic researchers, and industry leaders to create a consortium of vested experts to tackle this issue. To achieve this vision, we are spearheading a consortium of leaders to collaborate with LIM Innovations in response to requests for proposals around prosthetic outcomes-based projects. The goal of this consortium team is to advance outcome-based measures, prosthetic socket standards, and care models for those with amputations through improved technology solutions and efficient access to care.

A gold standard evaluation tool is not the only barrier to conducting outcomes-based research. People with amputations present as a varied clinical community and, with the exception of wounded active duty military personnel, are often found in small numbers across the United States. Access to patients for study recruitment is challenging, and high-quality functional and clinical data is often missing.

LIM Innovations has launched a patient registry to drive coordinated efforts around data collection and study recruitment. The patient registry provides a platform to gather functional feedback, compile a list of viable candidates for future clinical studies, and improve the quality and quantity of outcomes-based research. The registry captures user-driven feedback and satisfaction with their prostheses, particularly the prosthetic socket. It is intended to create an expansive database of individuals with amputations from multiple geographies and demographics. As the patient registry grows, research collaborations with clinical organizations will provide opportunities to match self-reported data with clinical outcomes. This is similar to the total joint arthroplasty registries seen in Scandinavian countries. Those registries have been exceedingly helpful in systematically identifying technologies and practices that result in suboptimal outcomes.

technicians in fabrication shop

Advancements in prosthetic sockets start with improvements in shop technology. The production team modifies a new socket order and makes adjustments to the socket during a clinical visit.

To replicate the depth and breadth of high-quality research and standardized outcome metrics recognized in other healthcare fields, the O&P industry needs to define gaps in the current standard of care. It is an all-inclusive effort between clinicians, patients, payers, and other industry agents to identify the biggest technology gaps and areas for improvement in patient care. As we identify the largest areas for improvement, introducing new technology and care models that yield high impacts becomes self-propagating in a value-added fashion.

Improving our standards for high-quality research will directly impact our ability to implement positive change in the industry. Clinicians will be able to improve the quality and efficiency of care, more easily introduce new technology into their practices, and justify their approaches and necessary technology to payers.

One of the most common themes among the LIM Infinite Socket users is dissatisfaction with their previous conventional socket fit. Even when provided with advanced distal prosthetic components, they did not achieve successful results with their prostheses. The best distal components are only part of the equation. After being fit with well-fitting sockets, the individuals were able to get the full benefit of their advanced distal components and resume active lives. Capturing unique metrics and outcome measures around these effects is the next step in improving access and the quality of care.

With more access to data, and wearable technology at the forefront of the digital world, connecting technology with the human body is becoming more prominent. LIM Innovations has utilized modularity and adjustability in socket design. The next step for the O&P industry is improving data collection and metrics around socket design. LIM Innovations is developing a platform to conduct quality research to make the next generation of prosthetic socket technology the standard of care. The key components after a shift in the conceptual value of the socket are then coming to a consensus on optimal metrics through consortium-related efforts and maintaining sophisticated data registries.

AK sockets


“Prosthetic care for amputees has had significantly less funding and subsequently less rigorous published comparative effectiveness research than other areas of healthcare with similar patient numbers (i.e., breast cancer, AIDS, and Parkinson’s) and healthcare resource expenditures. National Institutes of Health (NIH), the most prevalent government funder of clinical trials, is primarily a disease-driven funding institute. While many diseases lead to limb loss, funding from the NIH is nearly absent from the last 16 years of research on limb loss identified in a systematic review of evidence regarding lower-extremity amputation (in press). Only four high-quality evidence statements regarding the prosthetic socket interface were identified in this systematic review, mostly due to the lack of funding. So, if not the NIH, then who pays for prosthetic research? Prosthetic manufacturing companies fund efficacy trials of new devices, like a foot or a knee, but prosthetists fit and fabricate sockets; so the consolidated funds mostly do not exist to pay for high-quality interface clinical trials. The U.S. Department of Defense and U.S. Department of Veterans Affairs have both recognized the need for socket interface clinical trial research, and currently have several ongoing funded interface projects. However, these results will take time to disseminate. Pharmaceutical companies fund clinical trials; private prosthetic companies funding interface studies is a welcomed addition to our profession and may be the best hope for expedited evidence-based outcomes in evolving interface technologies.”

—Jason Kahle, MSMS, CPO, FAAOP

Andrew Pedtke, MD, is the CEO and cofounder of LIM Innovations, San Francisco. As a practicing orthopedic surgeon and visiting assistant professor at the University of California, Davis, Pedtke brings a critical vision to LIM Innovations and the O&P industry.

Kathleen Gallagher, MPH, is the director of research & policy at LIM Innovations. She is an epidemiologist and research administrator with experience working in the public, private, academic, and nonprofit sectors and deep understanding of real-world applications of public health practice.

Ranjit Steiner, BA, is the lead for user outreach and a support specialist at LIM Innovations. He is also an Infinite Socket wearer who uses his own experience and journalism background to bring out compelling stories.

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