Personalizing MPK Prescription for Individuals With Transfemoral Amputation
Phase: NA
Conditions: Transfemoral Amputation
Sponsor: Georgia Institute of Technology

 
 
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Title: Personalizing MPK Prescription for Individuals with Transfemoral Amputation 
NCT: NCT06399471 
Date: 04.08.24 
 
 
 
 

 
 
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Protocol for Personalizing MPK Prescription for Individuals With Transfemoral 
Amputation 
 
 
1. 
Study Aim, Background and Design 
Background: Published data shows approximately 35% of service members who sustain an 
amputation have it occur at the transfemoral level. Significant evidence indicates 
microprocessor knees (MPKs) have numerous benefits over non-MPKs for individuals with 
transfemoral amputation (TFA) including improved gait, safety, comfort, confidence, reduced 
falls, balance, patient satisfaction and reduced energy expenditure, greater ease in negotiating 
varying terrains, improvements in multi-tasking and cost effectiveness, such that MPK 
technology should be considered current state-of-the-art in TFA prosthesis prescription. 
However, studies which currently exist on MPK technology tend to lump the various knees 
together as a group rather than teasing out differences between the individual MPK technology 
and what types of patients are best suited for each. Therefore, a gap exists in clinical 
knowledge forcing clinicians to choose componentry based on reimbursement or their past 
experiences with an MPK, rather than detailed evidence supporting the use of one MPK for a 
certain individual. In this proposal, we will assess the biomechanical function and patient 
reported outcomes of each subject while they are using three commercially available MPKs 
and a research grade powered knee, addressing the FY20 OPORP Focus Areas “Prosthetic 
Device Function” and  “Prosthetic Device Form”.  
Hypothesis/Objective: Our objective is to personalize the prosthetic prescription process by 
creating a clinical decision algorithm for selection of an ideal MPK for an individual patient 
with transfemoral amputation (TFA) based on objective and patient reported data collected 
from that specific user. We test the central hypothesis that biomechanical and patient 
perceived differences will be detectable and predictable between different MPK components 
within a certain individual allowing for the creation of the first ever clinical decision algorithm 
for MPK component selection.  
Specific Aims: Aim 1 will assess functional performance associated with use and wear of 
three different commercially available MPKs and one research grade powered knee in 
17individuals with TFA. Aim 2 will assess subjective patient reported preferences associated 
with use of the same four prosthetic knees along with collection of subject specific 
anthropomorphic characteristics that may correlate with MPK choice. Aim 3 will generate the 
clinical decision algorithm for MPK selection.  
Study Design: Our study revolves around clinical tests and outcomes measures to evaluate 
the biomechanical performance and patient reported outcomes of three different commercially 
available MPKs and a single research grade powered knee in individuals with a TFA. We will 
test the hypothesis that differences will emerge between individuals when wearing the 
different knees and that these differences will be predictable. Subjects will ambulate over 
various terrains to simulate community ambulation with each MPK (Aim 1) allowing for 
assessment of the functional performance of each MPK. Through collection of individual 
anthropomorphic data and psychometric outcomes measures (Aim 2), we predict individual 
preferences and biomechanical improvements will emerge between the various MPKs 

 
 
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allowing for the generation of a clinical decision algorithm for MPKs (Aim 3).  
 
2. Participant population 
Subjects will be individuals with above the knee and below the hip amputation. This 
vulnerable population group will be protected through the use of safety equipment such as 
hand rails and a safety harness for the case of stumbles and falls. The goal is to collect data 
from at least 17 participants. 
Inclusion Criteria: 
You may participate in this study if you meet the following criteria: 
-A unilateral transfemoral amputation of the lower limb at least six months post fitting of 
definitive lower extremity prosthesis  
-Habitual use of a lower extremity prosthesis in daily living activities (based on 
assessment of a physiatrist and/or prosthetist and patient self-report) 
-Aged between 18 to 75 years  
-K3 or K4 level ambulators who can perform all locomotor tasks of interest (based on 
assessment of a physiatrist and/or prosthetist) 
 
Exclusion Criteria:  
You will be excluded from participating if any of the following apply to you: 
-Individuals with any significant neuromuscular or musculoskeletal disorder or other 
comorbidity that would interfere with participation (based on assessment of the physiatrist 
and/or prosthetist and patient self-report) 
-Individuals who have open wounds on their residual limb  
-Individuals with known visual impairments that would prevent them from safely 
operating a prosthesis during over ground walking or ascending stairs (based on 
assessment of the physiatrist and/or prosthetist and patient self-report) 
-Individuals with known hearing impairments or who use hearing aids that would prevent 
them from responding to an auditory instruction (based on assessment of the physiatrist 
and/or prosthetist and patient self-report) 
-Individuals who are currently pregnant (based on patient self-report) due to slight risk of 
falling during experiments 
 
All participants that meet the appropriate criteria will be recruited through official flyers and 
verbal scripts, even if they are already known to the researchers. Flyers will be posted 
around the campus of Georgia Institute of Technology as well as the general Atlanta 
community and in partnering clinical facilities, in designated advertising areas. Additionally, 
word of mouth recruiting will use a script with similar language as the flyers. The study may 
also be advertised during various outreach events (in-person and/or virtual). Advertisements 
may be sent out via email lists, patient advocacy websites and online forums, and other 
online resources including but not limited to our own lab websites. We will also request that 
our clinical colleagues and collaborators provide interested patients with information about 
the study and refer them directly to us if their patients are interested in participating. 
Recruiting materials are attached as separate documents including a flyer and e-mail script. 
Permission will be obtained from participants before using any information for research 
purposes that has individual identifiers attached.  

 
 
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3. Study Procedures 
Upon recruitment and informed consent, participants will proceed through the following protocol 
steps until they have been fit with all 4 prosthetic devices in total. 
 
Randomization & Blinding: The order with which each subject will be fit with an MPK will be 
randomized using a random number generator prior to enrollment. Subjects will not be blinded to 
device type as appearance of each device is a variable that may influence patient reported outcomes. 
Blinding of study personnel is not possible given that component-specific knowledge is required to 
tune each of the different MPKs. Data will be blinded for data analysis procedures to reduce any 
potential bias. 
Study procedures: 
1. Each device will be measured for length (overall build height) and weight prior to use in the 
study. Weight of devices will not be controlled due to anticipated effects on the outcomes and 
thus the final best selection. 
2. Anthropomorphic data will be collected from each subject to include cause of amputation, K-
level, waist circumference, leg length, residual limb length, build height between distal residual 
limb and knee center, weight, height, BMI, gender and age. These variables are unique 
characteristics associated with an individual which may have an impact on their successful use 
with one device over another. This data will only need to be collected once from each individual 
participant. 
3. Subjects will be administered the Patient Scales of Preference and Importance survey to 
understand how they individually rank priorities with regards to their prosthetic care and aspects 
of their daily life. The AMPnoPro will be administered to the subject while they are not wearing 
their prosthesis to attempt simulation of a patient with a new amputation that has gone through 
physical therapy and ready for a definitive prosthesis. AMPnoPro has been shown to be 
predictive of the functional level of an amputee. [1] 
Subjects will then undergo fitting and alignment of the prosthetic knees in a randomized order.  
4. Acclimation time varies widely in the literature (from 3-10 hours [2, 3] to months [4]) and is 
acknowledged to have important implications for this study’s results. In this study, subjects will 
go through an initial tuning and training process similar to what is done in clinic scenarios 
including tuning knee parameters and training over the various terrains in the lab including stairs, 
ramps and a treadmill. Subjects will then proceed to wear the prosthesis for 1 week at home and 
in the community in order to acclimate to the device and then return to the lab for testing. A 
sensor to collect data about the number of steps participants take will be attached to the prosthesis 
and/or your shoes. This sensor does not have a GPS and will not record where subjects go. 
Subjects will use their same socket, prosthetic foot and shoe during each knee evaluation to 
ensure that differences observed during the study are attributable to the knee.  
5. Subjects will ambulate five times over the 18’ instrumented gait mat to determine their self-
selected walking speed (SSWS) and GVI. Subjects will complete a 2-minute walk test and then 
be administered the Borg RPE.[5] A heart rate monitor will be worn during the 2 minute walk 
test in order to calculate physiological cost index (PCI) [6] 
6. Subjects will proceed to walk up and down an overground 5-degree ramp for ten trials and then 
walk up/down a 6-step stair case for ten trials while we measure lower body 3D biomechanics 
and completion speed.  

 
 
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7. Subjects will walk across a beam while wearing the prosthesis. The beam is very low in height 
and sits only ~2” inches off the ground. 
8. Subjects will walk on a treadmill while wearing the prosthesis while we measure lower body 3D 
biomechanics.  
9. Subjects will then fill out the OPUS HRQOL, LEFS, PEQ, Veteran SF-36, and fall history survey 
to assess their perception of performance and other health related quality of life factors associated 
with use of each device. Pilot work with these surveys indicates this will take approximately 30-
45 minutes. 
10. Subjects will repeat Steps 4-8 with periods of rest provided as necessary until they have 
completed the full protocol for each of the three MPKs and research grade powered knee. 
 
During all testing participants are instructed to vocalize any concerns or discomfort to 
researchers. Tests that occur in the lab will occur with the use of a safety harness and or gait 
belt. During tests, verbal feedback from the participants will be used to improve the comfort of 
the devices. Participants are instructed to notify researchers if they feel unsafe, and may quit the 
study at any time without penalty. Additionally, participants may be asked to wear EMG sensors, 
markers for measuring biomechanics and other mechanical sensors (such as IMUs) All 
participants will be guided through the following general procedure during their visits, requiring 
action on their part: 
● Participants will be briefed about the details of and their rights during the 
study. 
● The prosthesis and attachment interface will be fit to the participant, along 
with any additional data collection equipment. 
● Participants will be guided through the specific activities of the study, 
detailed already. 
● Participants will receive assistance removing any sensors used during the 
study. 
Other equipment may be utilized to measure biomechanics of the user during 
ambulation. Specifically, we will be using a VICON motion capture analysis system and an 
instrumented treadmill. This will also us to measure biomechanical similarities and 
differences while using the powered prosthesis compared to the sound side limb. Also, 
some protocols will require the use of an EMG (electromyography) system to measure 
muscle activity across different ambulation tasks. Three systems may be used which 
includes the Delsys Trigno Wireless EMG system, Biometrics Ltd. EMG system, and 
COAPT EMG system. All of these systems will use electromyography sensors that will be 
placed on the surface of the user’s skin. 
In order to also measure functional clinical measures, a Protokinetics gait mat will be 
utilized to measure common measures such as step length, step time, and symmetry. This 
system is just a mat that users will need to walk on top similar to walking overground. Users 
will be in a harness and have the options for handrails or gait belt if needed.  
Throughout the tests there will be a camera recording the session. The purpose of 
the camera is to record performance for future analysis. The participant will always have the 
right to stop the test and/or take a break. The participant may also choose to discontinue 
participation at any time. 

 
 
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During the first visit, fitting and tuning will be no longer than 4 hours. Participants 
may end the visit at any time without penalty, or choose not to return for additional visits. If 
the participant agrees to continue the study subsequent visits will be scheduled at their 
convenience and pending availability of the prosthetic knee joints. During these subsequent 
visits, testing will last between 2­6 hours based on participant comfort. 
Participants will be asked to attend at least 5 sessions in order to compare the 
effectiveness of the different prosthetic knees. However, each participant will 
maintain the right to discontinue their involvement for future sessions. Depending on the 
progress of the tests, participants may be involved in sessions ranging over the course of a 
few months. 
The results of the study will be in the form of device performance and participant 
feedback. Sensor data will record the movement parameters of the subject. This includes 
mechanical instruments on the device and biomechanical instruments attached to both the 
device and the human subjects. These instruments will give information about the 
kinematics (movement), kinetics (force), muscle activity, step count, heart rate and 
metabolics of the user. This allows for the effectiveness of the design strategy to be 
assessed. The participants will also give feedback in the form of verbal conversation. This 
verbal feedback will deal with the comfort, convenience and preferences of the devices and 
controllers. 
This study will use statistical analysis to compare between different intent recognition 
systems. We will use intent recognition accuracy as the primary metric to compare statistical 
differences across conditions. We will compare biomechanics between the powered device 
and a passive prosthesis. Typically, ANOVA tests are used with repeated measures to 
compare across multiple conditions. 
Statistical & data analysis plan 
A repeated measures ANOVA with within factor MPK will be used to assess 
differences across treatment for Aims 1 and 2, provided assumptions are met.  In the event of 
missing data or violation, a linear mixed models procedure, which does not assume 
compound symmetry, will be considered.  Bonferroni-Holmes correction will be made to 
control for family-wise error rate.  Samples size calculations are outlined below.  Estimated 
effect size was calculated using Cohen’s d for within factor designs [71], assuming a 
correlation among repeated measures of 0.5.  Effect sizes were then converted to Cohen’s f 
for sample size estimations using G*Power. [72] Aim 1:  Comparison of clinical outcome 
measures on MPKs.  A Borg RPE of 2 (pooled SD= 2) was deemed clinically relevant for 
this study, resulting in an effect size of 1.  Gait variability index effect size was based upon 
minimally detectable change (MDC) cited in [73].  An MDC of 8 and hypothesized pooled 
SD of 6, produced an effect size of 1.3.  These data indicate a sample size of approximately 9 
will achieve 90% power.  The sample size proposed in this study (N=12) should ensure 
adequate power, even in the event of attrition or slightly higher variability. Aim 2:  Patient 
reported outcomes. Resnik & Borgia (2011) have suggested a MDC of 10.3 (90% CI) for 
OPUS lower limb function.[61]  Effect size for this study was calculated using MDC of 10 
and a pooled SD of 7.7, assuming higher variability than previously reported SD’s for upper 

 
 
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extremity [73].  This resulted in a Cohen’s D of 1.3.  Resnik & Borgia (2011) also reported 
PEQ subscale MDC’s which ranged from 0.8-1.4 with Std errors of 0.3-0.6.[61]  Based upon 
an MDC of 1.1 and SD of 1.25, Cohen’s d would be 0.88.  The sample size of 9 corresponds 
to 80% power. The SF36V will be used as an additional measure of health related QOL but 
due to high variability reported in the literature (from the inclusion of both mental and 
physical function scales)[61], this measure will not be powered by this preliminary study. 
Instead, this measure will be used to look for clinical trends in the data and aid in potential 
direction for the future larger study outlined in our transition plan. Aim 3: Clinical Decision 
Algorithm. The creation of the clinical decision algorithm for personalizing the MPK 
prescription to an individual is an exploratory, informative analysis that is constrained by 
population size and resources. Repeated sampling is employed to increase the information 
gained while attempting to minimize within subject variability and provide better 
examination of relationships. It is expected that in initial development, large effect sizes will 
be detected which play a critical role in the satisfaction with the use of prosthetic devices. To 
be valuable to clinical decision making, it is imperative that identification of this causal 
mechanism include factors other than solely clinical measurements. In addition, proximal 
outcomes, based on existing knowledge, will supplement the model. This process will lay the 
groundwork for the decision tree to be refined over time as the sample can be increased. 
There are a number of models that can be used for this aim (Bayesian approaches, linear 
discriminant analysis for repeated measures, etc.) which do not require as large a sample size 
for estimation procedures. The choice of model will be determined based on the underlying 
data structure by our co-I biostatistician, Dr. Teresa Snow. 
 
4. Research Risks 
The prosthetic knees have hydraulics and sensors. This type of device is classified 
as a prosthetic component and is a FDA Class I device. This means that it is a low-risk type 
of medical equipment. Although these procedures are very safe and commonly used in our 
lab, participation in this study may involve the following risks: The primary risk of injury in 
this protocol would be due to falls, regardless of the prosthesis being used. To minimize this 
risk, participants will be asked to wear a safety harness and initially walk with handrails until 
they become comfortable using the prosthetic device(s) and demonstrate that they can use 
it without falling. Should participants fall during this familiarization session, the harness will 
support them. When walking overground, participants will still have the option of wearing the 
safety harness, access to hand rails or other walking aids, and may be supported by staff 
members using a gait belt as you complete the activities. When participants wear the 
prosthesis at home, they will not have access to a harness or gait belt. This is similar to 
what happens in clinical scenarios when a prosthetist fits a patient with a prosthetic 
component; while in the clinic, familiarization occurs and then the patient is sent home to 
use the device independently. 
 
A second risk is muscle soreness and fatigue. Muscle soreness is a common 

 
 
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problem when walking with a new prosthesis. To prevent this, experimental sessions will be 
kept as short as possible, adequate rest periods will be provided between trials, and 
participants will be questioned often about any discomfort.  
 
A third risk is skin irritation. Skin can become irritated while using any prosthesis and 
it may also become irritated by adhesive reflective markers. Additionally, the residual limb 
will be checked prior to and after the study to inspect for skin irritation or if participants 
experience discomfort in their residual limb during the study, we will give time for the socket 
to be removed to allow for appropriate inspection. To avoid the risk of skin irritation, 
participants will use your normal, take-home socket.  
 
A fourth risk is that participants may find that they prefer a different prosthetic knee 
following use of the various knees within the study and may not be able to obtain this knee 
through your clinical provider and/or insurer. We will provide all information to you that you 
request regarding your performance in the various knees but the goal of the study is not to 
provide participants with a knee to take home following the study. 
 
5. Confidentiality 
Participants will sign a consent form before participating which explains that no 
identifiers linking them to this study will be included in any sort of report that might be 
published except for the video taken. Participant faces will be blocked out upon request. 
They will be given a pseudonym different from their own name that will be referred to in 
studies published, if at all. Participants will be assured in the informed consent that the data 
will be used only for studies that are consistent with the original research purpose. 
This consent form will be filed securely in an official area. People who have access 
to information include the Principal Investigators and research study personnel. 
Representatives of regulatory agencies such as the Office of Human Research Protections 
(OHRP), the Food and Drug Administration, the DoD, and entities such as the Georgia Tech 
Office of Research Integrity Assurance may access participant records to make sure the 
study is being run correctly and that information is collected properly. 
Information about participants related to this study will be kept confidential to the 
extent permitted or required by law. 
When the data is stored, it will no longer be linked to the subject's personal 
information. There will be a master list stored separately that connects the subject identifiers 
with their personal information, for when they need to be contacted. The data will be kept on 
the computers of the research personnel only. These computers will all be password 
protected to prevent non­authorized access to the data. Data will be transmitted 
electronically between researchers. The master list of subjects and their personal 
information will not be transmitted in any form between researchers. This master list will only 
be in the possession of the PI and researcher responsible for recruiting. It will not be shared 
with anyone else in any way. 
 
6. Benefits 
Our goal is to optimize the prosthetic prescription process for currently available 

 
 
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MPK devices as there is no current understanding for which MPKs are best suited for which 
patients. The long-term goal of this research is to improve the ability of people with 
amputations to be able to walk better and more easily: including walking on level surfaces, 
stairs, ramps, hills and other activities. 
 
7. Compensation 
Subjects will be paid at $20/hour while they are in the lab and an addition $300 once 
they complete the full study to incentivize all subjects to complete the full study which is 
important for our results. Free parking will be provided to all subjects when they come to 
campus for experimental sessions. 
Subjects will be given the choice of compensation via check which will be issued 
through USPS mail to their home (or a provided) mailing address or a gift card 
which will provided at the end of each visit to the lab. 
 
8. Costs 
There are no direct costs to study participants. The costs to participants for this 
study will most likely be only their time and energy. Participants will be responsible for 
covering any unforeseen costs including, but not limited to, transportation to the research 
location, parking expenses, food, or child care. 
 
9. Alternatives 
Participants are informed that participation in this study is voluntary. It is made clear 
that they have the right to change their mind and leave the study at any time without giving 
any reason and without penalty. Any new information that may make participants change 
their minds about being in this study will be given to them. 
 
10. Consent/Assent Process and Documentation of Consent/Assent 
After being informed about the study through recruitment by way of flyers, e-mail or 
word of mouth, participants will be given a consent form outlining details about the study. 
The consent form provides detailed information about the study procedures. When reading 
through the consent form potential participants are encouraged to vocalize any questions 
they have including, but not limited to, inquiries about testing procedure, risks of the study 
and participant rights. Questions will be answered by the researcher personnel conducting 
the study. Participants will be given as much time as they need to make a decision about 
whether or not to participate. During this process, as well as throughout testing it will be 
made clear that participants may chooses to end the study at any time, no questions asked, 
and will not face any negative repercussions. Signing of the consent form will take place in 
person where researchers present will answer any questions then obtain their signatures. 
This consent form will be filed securely in an official area, that can only be accessed by 
Principal Investigators of this  study and research study personnel. Participants will be given 
a copy of this consent form and do not waive any legal rights by signing it. 
The only personal information we will collect is the participant's name, telephone, 
email, and contact information. This information will not be published in the research results, 
nor will it be used to perform data analysis. This information will also not influence the 

 
 
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results of the research. We only collect this information so we can contact the participants 
and refer to them by their names during conversation. 
 
11. Investigator’s Qualifications 
The PI, Dr. Aaron Young, has conducted a number of experiments similar to this one 
with amputees. The Co-PI, Kinsey Herrin, is a certified prosthetist specifically trained to 
work with individuals with amputation and fit prosthetic devices to them. Three of the 
prosthetic knees used in this protocol are clinically available through manufacturers and 
used broadly in the prosthetics clinical community. These are the devices that will be 
brought home for 1 week testing protocols with participants. The fourth device is our own 
experimental investigational device and the testing of this device was IRB approved 
previously at Georgia Tech with a separate, but related protocol. All members listed on this 
IRB protocol have CITI training. 
 
12. Funding Sources 
This work is funded by the Department of Defense through the Congressional 
Directed Medical Research Program (CDMRP). The grant title is Personalizing MPK 
Prescription for Individuals With Transfemoral Amputation. None of the researchers involved 
in this study have conflict of interest. 
 
 
References 
1. 
Gailey RS, Roach KE, Applegate EB, Cho B, Cunniffe B, Licht S, et al. The Amputee 
Mobility Predictor: An instrument to assess determinants of the lower-limb amputee's ability to 
ambulate. Archives of Physical Medicine and Rehabilitation. 2002;83(5):613-27. doi: 
https://doi.org/10.1053/apmr.2002.32309. 
2. 
Thiele J, Schöllig C, Bellmann M, Kraft M. Designs and performance of three new 
microprocessor-controlled knee joints. Biomedical Engineering/Biomedizinische Technik. 
2019;64(1):119-26. 
3. 
Johansson JL, Sherrill DM, Riley PO, Bonato P, Herr H. A clinical comparison of variable-
damping and mechanically passive prosthetic knee devices. American journal of physical 
medicine & rehabilitation. 2005;84(8):563-75. 
4. 
Orendurff MS, Segal AD, Klute GK, McDowell ML. Gait efficiency using the C-Leg. Journal 
of rehabilitation research and development. 2006;43(2):239. 
5. 
Borg GAV, Noble BJ. Perceived Exertion. Exercise and Sport Sciences Reviews. 
1974;2(1):131-54. PubMed PMID: 00003677-197400020-00006. 
6. 
Fredrickson E, Ruff RL, Daly JJ. Physiological Cost Index as a proxy measure for the 
oxygen cost of gait in stroke patients. Neurorehabilitation and Neural Repair. 2007;21(5):429-34. 
 
 
 
 
 
 

 
 
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