For most people, a bump from a passerby on the sidewalk, a hike on an uneven trail, or even carrying a shopping basket in the grocery store doesn’t affect mobility. However, these everyday encounters and activities can present unpredictable challenges for those who wear a lower-limb prosthesis.
Understanding mobility challenges like these—and addressing them using feedback obtained directly from prosthesis users—is a primary, yet elusive, goal for rehabilitation physicians, prosthetists, and researchers alike.
Now, an instrument called the Prosthetic Limb Users Survey of Mobility (PLUS-M) 
, developed with funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), is helping reach this goal through an easy-to-use measurement system. Widespread use of the tool in clinics worldwide, including at a leading U.S. orthotic and prosthetic healthcare provider, is changing the rehabilitation landscape.
Created by a team of researchers at the University of Washington, the PLUS-M is a brief questionnaire that allows respondents to convey their perceptions of how they complete actions at home or in daily life, such as descending a staircase or crossing a slippery floor. Clinicians and researchers use the PLUS-M to assess individuals’ mobility in clinical practice and scientific studies.
Building an instrument based on patient-reported outcomes rather than a clinician’s subjective assessment was a novel and exciting approach when the project started in 2010, said Toyin Ajisafe, Ph.D., a program officer at NICHD’s National Center for Medical Rehabilitation Research. Historically, health questionnaires were developed by clinicians and researchers based on their views and interpretations of patients’ limitations. Such surveys were also administered by intermediaries, adding yet another layer between the patient and the information.
“This project was refreshing because it focused on the user’s experiences and standpoint. It captured a side we don’t typically look at,” Dr. Ajisafe said.
Principal Investigator Brian J. Hafner, Ph.D., a professor in the Department of Rehabilitation Medicine at the University of Washington, and his team knew that they wanted to focus on daily mobility challenges for lower-limb prosthesis users with various amputation levels. To ensure that they were incorporating the patient perspective, they used the comprehensive blueprint established by NIH’s Patient-Reported Outcomes Measurement Information System to build this self-report tool.
With help from clinics, industry partners, and other stakeholders, they assembled focus groups of prosthesis users to create survey questions and then conducted cognitive interviews to determine whether the questions were clear and understandable to respondents. They revised or deleted questions based on user feedback before administering the candidate questions to more than 1,000 prosthetic limb users across the country. Results of the study were used to finalize the PLUS-M survey.
The team gradually narrowed the bank of survey questions from 105 to 44 before conducting additional studies to investigate the psychometric properties—reliability, validity, and sensitivity—of the PLUS-M outcome measures. The result is an easy-to-complete survey of 7 or 12 questions that patients can take on paper or by computer. The electronic version, known as a Computerized Adaptive Test (CAT), uses an algorithm to select the next item based on a users’ previous responses. For example, if a user responds “without any difficulty” to the question, “Are you able to walk a short distance in your home?” the CAT will ask a tailored follow-up question such as “Are you able to walk across a parking lot?”
The PLUS-M is quickly becoming part of standard practice for assessing patients in the clinic. Danielle Melton, M.D., a visiting associate professor in physical medicine and rehabilitation at the University of Colorado, Anschutz, said amputation-specific, patient-reported outcome measures such as the PLUS-M are becoming widely accepted tools for measuring progress and informing therapeutic goals. Though the PLUS-M is a “snapshot in time,” it can be a powerful aid in guiding care.
“You can use the tool to compare ‘this is where you were before, and this is where you are now.’ I'm able to take that information and offer specific solutions,” Dr. Melton said. “The PLUS-M can help justify medical necessity, such as the need for a new socket, or possible reasons for additional safety features or prosthetic components that can result in improved function and quality of life for that patient.”
Hanger Clinic, a leading provider of orthotic and prosthetic care in the United States, has integrated the PLUS-M into its more than 900 patient care clinics nationwide since 2016. Clinicians use the PLUS-M—and patient-reported clinical outcome measures more broadly—to adjust care plans based on a patient’s dynamic condition, said Shane Wurdeman, Ph.D., vice president of scientific affairs at Hanger Clinic. The tool’s design, flexibility, and brevity are appealing for both patients and clinicians.
“Patients feel they provide important information without becoming overwhelmed by the process,” Wurdeman said. “We also provide a patient’s outcome score in the context of their peers, and they really love having the ability to understand and answer the question: ‘Am I doing as well as I should be?’”
Hanger Clinic also uses the PLUS-M to perform large-scale analyses of outcomes across its locations, providing both patient and population outcomes to the wider orthotic and prosthetic care community. As of May 2023, Hanger used the PLUS-M in 14 peer-reviewed studies, including a recent analysis of nearly 30,000 patients with lower limb amputations.
Developed as a non-commercial tool, PLUS-M is now part of various orthotic and prosthetic electronic health record (EHR) systems, including OPIE, Nymbl, and the U.S. Department of Veterans Affairs’ EHR system. It is available in patient software systems, such as PatientIQ and FOTO, among others, and is licensed by several hospital systems, including those of the Johns Hopkins University, University of Michigan, and Gillette Children's Specialty Healthcare. PLUS-M also reaches international audiences with translations into more than 20 languages, including Spanish, Arabic, and Swahili.
PLUS-M’s utility and adoption in the clinical setting inspired Dr. Hafner’s team to develop similar tools for other audiences. In 2022, his team released Orthotic Patient-Reported Outcomes - Mobility , a survey similar to PLUS-M, to evaluate mobility among people who use lower-limb orthoses, or braces. Dr. Hafner and his team, along with collaborators from Virginia Commonwealth University and Hanger Clinic, recently received funding to expand their work into patient-reported outcome measures for upper limb prosthesis users.
“Twenty years ago, outcomes measurement—especially those that incorporate data collected directly from users—wasn’t really part of day-to-day prosthetics practice. Today, the use of tools and self-reports like PLUS-M is often routine. I’d like to think that our efforts to create these instruments and share the knowledge we’ve gained from using them have helped to facilitate this important change in our field,” Dr. Hafner said.
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