Outcome Measures: Avenues for Optimizing Prosthetic Performance

By Vibhor Agrawal, PhD, ATP

Are you optimizing prosthetic performance in your patients? Is improved performance translating into better health for your patients? Are you measuring outcomes to document the health-related benefits of the prostheses you provide to your patients?

The need to measure and evaluate prosthetic outcomes has become a hot topic in the current healthcare environment. Outcome measurements may become a necessity for reimbursement in the near future as some payers are subscribing to the philosophy that anything that was not measured was not done and therefore should not get reimbursed.

Currently, the use of outcome measures in prosthetic clinics is negligible as clinicians are accustomed to using "clinical measures," which require professional knowledge for interpretation. These clinical measures may correlate poorly with "standardized outcome measures" and may not always predict important health-related outcomes. The limited use of standardized outcome measures can be attributed to lack of time needed to administer these measures, limited knowledge on the availability of outcome measures, and unfamiliarity with the appropriate measures. (Editor's note: This article builds on some of the outcome measurements introduced in Phil Stevens' article, "The Knee-ds of the K2 Transfemoral Amputee," The O&P EDGE, December 2012, and provides a comprehensive list of outcome measurements.)

Healthcare outcomes by definition are the changes in patients, related to their health status, behavior, and satisfaction that can be attributed to the treatment they received.1 Prosthetic outcomes can be defined as changes in the functional level, health, and quality of life attributable to the prosthetic device. As a result, outcomes with a prosthesis are not only determined by the prosthesis itself, but also by patient-specific factors such as his or her overall health. A well-fitting socket along with technologically advanced components does not guarantee optimal performance because, contrary to popular belief, a prosthesis is not a device that is simply replacing the missing body part. It is a medical appliance that can significantly impact the user's health and quality of life. While a well-fitting prosthesis is essential for optimal performance, factors related to function and confidence also alter your patient's performance appreciably and can therefore influence outcomes.

Measurement of outcomes is a systematic approach for evaluating the quality of care and effectiveness of treatment that you provide to your patients with amputations. By incorporating outcome measures in daily practice, you have the ability to evaluate the various aspects of clinical care, such as confidence level with the prosthesis, socket comfort, functional level, and quality of life. Outcome measures can determine the effectiveness of an intervention, detect cause for concern, and in some cases direct you to potential solutions. By documenting changes in outcome measures over time, you can assess the value of treatment you provide and possibly enhance outcomes by offering positive feedback to patients on their progress. You also have the ability to demonstrate to caregivers and insurers the extent to which your treatment improves the patient's health and reduces healthcare costs.

Outcomes can easily be measured three different ways: self-report measures or patient-reported outcomes, performance-based measures, and biomechanical measures.

Self-Report Measures or Patient-Reported Outcomes

These are reports directly from the patients, which reflect their preferences and perceptions. Patients assess constructs such as symptoms, satisfaction, function, health perceptions, and quality of life. The following five tools are examples of self-report measures:

1. The PEQ2 consists of 82 questions that describe the function of a lower-limb prosthesis and assess prosthesis-related quality of life. The questionnaire is divided into ten functional scales, addressing four major domains: prosthetic function, mobility, psychosocial experience, and well-being. There are seven groups of questions, which can be used and scored independently of the others. A subset of the PEQ, called PEQ Mobility Scale (PEQ-MS) consists of 12 questions and was designed to assess locomotor ability while using a prosthesis. The PEQ-MS can be administered in five minutes.

2. The PPA3 evaluates lower-limb prosthetic use in terms of frequency of prosthetic wear and the level of ambulatory function with the prosthesis. The 44 questions are grouped into six basic sections: physical condition, the prosthesis, prosthetic capabilities, the environment, leisure activities, and demographic characteristics. Each section is scored independently, and a composite score cannot be calculated for the six sections. This questionnaire is available in six different languages and takes about 25 minutes to administer.

3. The LCI4 evaluates the level of independence when performing ambulatory activities and provides a composite score for basic and advanced activities. The 14 questions measure patients' perception on performing various activities, either independently or with the assistance of a caregiver or an ambulation aid. The questionnaire is available in seven different languages and can be administered in five minutes either over the telephone or in person.

4. There are four components of OPUS.5 The first component, lower-limb functional status, consists of 20 questions that assess activities of low, moderate, and high difficulty on a five-point scale ranging from "very easy" to "cannot perform activity." The quality of life component contains 23 questions regarding high, average, and low quality of life aspects on a five-point scale ranging from "not at all" to "extremely." The third and fourth components of the tool, satisfaction with device and satisfaction with service, consist of 11 and ten questions, respectively, and are rated on a four-point scale ranging from "strongly agree" to "strongly disagree." This questionnaire takes about 20 minutes to administer.

The OPUS questionnaire also has an Upper-Extremity Functional Status (UEFS) module, that assesses the ease of performing 23 selfcare and instrumental activities of daily living (ADL),6 on a five-point scale ranging from zero, "cannot perform activity," to four, "very easy to perform the activity".

5. TAPES7 has been designed to assess the physical and psychosocial aspects of adjustment to a prosthetic limb. It consists of 40-60 questions related to psychosocial adjustment, activity restriction, and prosthetic satisfaction domains. The total number of questions to be answered varies depending on the patient's responses. The questionnaire is divided into two parts, and uses a combination of a five-point rating scale, "strongly agree" to "strongly disagree," a three-point point rating scale, "not at all limited" to "limited a lot," and "yes/no" responses. It can be used to evaluate changes in quality of life during the rehabilitation process. This questionnaire takes about 25 minutes to administer.

6. PLUS8 is a collection of outcome measurement instruments that are currently being developed with the intention of measuring attributes of mobility, balance, and dexterity. The first subset, called PLUS-Mobility (PLUS-M), was developed in 2012 and is currently undergoing longitudinal testing. The current version of PLUS-M includes 12 questions that assess mobility with a prosthetic leg and are answered on a five-point scale ranging from "unable to do" the activity to able to do the activity "without any difficulty." This questionnaire can be administered in five minutes.

7. DASH9 is used to assess the impact of upper-limb amputation on physical function and also to observe changes in function and symptoms over time. It consists of 30 questions that are scored using a five-point scale from one ("no difficulty" in performing the activity) to five ("inability" to perform the activity). A composite score for all 30 items is calculated, with a higher score indicating greater disability or greater functional limitation.

Performance-Based Measures

These measures evaluate the performance of patients during a task or a group of tasks. Performance is scored in terms of either the time needed to complete the task, the distance covered, or the patient's ability or inability to do the task. The result of these measures is typically a number that can be compared across different patients or for the same patient at different time intervals during the rehabilitation process.

Amputee Mobility Predictor (AMP)10: This test is a measure of functional ambulation capabilities of people with lower-limb loss. It can be performed by patients with or without a prosthesis (AMPPRO and AMPnoPRO, respectively). It consists of 21 tasks, classified into four categories: sitting balance, simple mobility, standing balance, and gait and functional activities. This test can be administered in ten-15 minutes.

Comprehensive High-Activity Mobility Predictor (CHAMP)11: CHAMP is a measure of agility typically used to test high-level performers who tend to max-out their ratings on other performance-based measures. This measure includes activities that are designed to test motion in all three planes, like turning, cutting, side-to-side movement, and backward running. It consists of four tasks and can be administered in 15-20 minutes.

Timed Up and Go (TUG) Test12: Originally the TUG was designed to test basic mobility skills of frail, elderly persons. It is now being increasingly utilized to test functional mobility in people with lower-limb loss. While performing the test, patients stand up from a chair, walk ten feet, turn and return to the chair, and then sit on the chair. This measure tests a number of tasks that are essential for mobility, such as standing from a seated position, walking, turning, and sitting down on the chair.

Six Minute Walk Test (6MWT)13: The 6MWT evaluates functional capacity as the individual walks for six minutes on a hard, flat surface. The goal for patients is to cover as much distance as possible in six minutes by pacing themselves and resting as needed. A variation of this test is the two-minute walk test, during which the patient is asked to walk for two minutes. The six-minute walk test can also be used to detect changes in physical activity following an intervention.

Berg Balance Scale (BBS)14: This scale was developed to measure balance and to predict the fall risk in people with balance impairments. It consists of 14 functional tasks related to sitting, standing, turning, and transfers. Each task is scored on a five-point scale ranging from zero (lowest level of function) to four (highest level of function). A composite score is calculated, and low, medium, or high risk of fall is determined based on the score. This test can be administered in 15 minutes.

Southampton Hand Assessment Procedure (SHAP)15: SHAP is a hand function test that was originally developed to assess the effectiveness of upperlimb prostheses. The individual is asked to perform 26 tasks-14 ADL tasks and eight tasks with abstract objects, which are classified into six prehensile patterns. Time needed to complete each task is recorded, and a composite score is generated. Scores less than 100 indicate impairment in hand function.

Biomechanical Measures

Biomechanical outcome measures can be classified as kinematic, kinetic, and temporal-spatial parameters. While it may not be possible to measure all outcomes in a clinical setting, recent advancements in wireless technology and mobile computing have led to the development of clinically friendly equipment that can measure selected biomechanical parameters.

  • Symmetry in External Work (SEW)16: This measure of gait dynamics assesses the symmetry of work between lower limbs, that is the effort provided by each limb in moving the body during ambulation. It can be calculated easily using in-sole sensors and with minimal attachments on the patient. This measure can also be used for activities such as ramp and stair ambulation in addition to level walking and has been used to detect differences between different prosthetic feet.
  • Gait Mats: Clinicians are often interested in assessing temporal or spatial symmetry between the lower limbs, such as stance time or step length. A gait mat can prove useful for such applications as it is quick and easy to use, portable, and requires no subject intervention. Some gait mats provide the option for measuring plantar pressure and center of mass trajectory.

While a number of outcome measurement instruments are available, a universal measure that is consistently used by clinicians and researchers for evaluating prosthetic outcomes is lacking. The best clinical practice is to apply the measures that are most relevant for your patients based on the idealized level of prosthetic outcomes. Some of the validated measures may be limited in their ability to assess the attributes of your interest effectively and may not be ideal for a particular patient. In such cases, it is beneficial to use the most appropriate standardized outcome measure and supplement it with an additional outcome instrument that works for you. Since the standardized measures are reliable and valid, they can act as powerful tools not only for improving prosthetic outcomes but also for justifying the treatment plan to third-party payers. The high demands of an effective prosthetic practice can lead clinicians to focus exclusively on providing the optimal prosthesis with the perfect alignment, which could sometimes obscure the "big picture" of overall patient health. By utilizing the appropriate outcome measures, you will be able to get an overall idea of the health of your patients, improve prosthetic performance and satisfaction, and reduce ancillary healthcare costs.

Vibhor Agrawal, PhD, ATP, specializes in amputee movement biomechanics and outcome measurements. His research is directed towards reducing secondary medical conditions and enhancing performance in people with amputations. He can be reached at


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