Computational Design, Fabrication, and Evaluation of Optimized Patient-Specific Transtibial Prosthetic Sockets
Phase: NA
Conditions: Amputation Stump
Sponsor: Massachusetts Institute of Technology

COVER PAGE 
Document Type: 
STUDY PROTOCOL
Official stutuay title:
 Computational Design, Fabrication, and Evaluation of Optimized 
Patient-Specifc Transtibial Prosthetic Sockets
NCT number: 
not yet assigned
Document Date: 
02/15/2018
Principal investutigator: 
Prof. Hugh Herr
Sponstuor: 
NIH
Participating stuitestu: 
Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
McGovern Institute for Brain Research, MIT, Cambridge, MA, USA

STUDY PROTOCOL
I.
BACKGROUND AND RATIONALE
The overall goal of this study is to further develop, and clinically assess, a computational and data-
driven design and manufacturing framework for mechanical interfaces that quantitatively produces 
transtibial prosthetic sockets in a faster and more cost-efective way compared with conventional 
processes.
In the United States, 623,000 people live with major lower extremity loss, with that population 
expected to double by 2050 [1]. The U.S. Department of Veterans Afairs estimates lower extremity 
amputation (LEA) to account for more than $250 million in direct expenditures each year, not 
including civilian cases [2]. Complications of prosthetic leg use in persons with LEA often occur at the 
prosthetic socket, and includes delayed wound healing, recurrent skin ulcerations, and pressure 
damage to soft tissues [3]–[6]. Such complications can result in limited mobility, which further 
contributes to conditions such as obesity, musculoskeletal pathologies, and cardiovascular disease 
[7]–[9]. Conventional prosthetic socket fabrication is an artisanal process requiring substantial human 
hours, fnancial cost and patient involvement for evaluation. Computer aided design (CAD) (e.g.[10]–
[13]) and computer aided manufacturing (CAM) (e.g.[14]–[24]) methods have been explored as an 
alternative. However, these tools have not reached full clinical efcacy and do not inform the design 
in a data-driven sense since the actual design process remains a manual and experience-based 
procedure [25]. The long-term goal of our research is to develop a fully-quantitative process for 
prosthetic socket design and production that requires minimal patient involvement and can be 
delivered at afordable price points.
In pursuit of our long-term goal, our team has recently developed a framework for prosthetic socket 
design and fabrication [26] that involves: 1) non-invasive imaging to record patient geometry, 2) 
indentation to assess tissue mechanical properties, 3) data-driven and automated creation of patient-
specifc designs, 4) patient-specifc fnite element analysis (FEA) and design evaluation, and 5) 3D 
printing of the end design for clinical evaluation. 
II.
OBJECTIVES
The overall goal of this study is to further develop and clinically assess a computational and data-
driven design and manufacturing framework for mechanical interfaces that quantitatively produces 
transtibial prosthetic sockets in a faster and more cost-efective way than conventional processes. 
Traditionally, prosthetic socket production has been a craft activity, based primarily on the 
experience of the prosthetist. Even with advances in computer-aided design and computer-aided 
manufacturing (CAD/CAM), the design process remains manual. The manual nature of the process 
means it is non-repeatable and currently largely non-data-driven, and quantitative data is either not 
obtained or insufciently employed. Furthermore, discomfort, skin problems and pressure ulcer 
formation remain prevalent. Through the proposed computational modeling framework, a 
repeatable, data-driven and patient-specifc design process is made available which is based on 
scientifc rationale. 

Objective/hypothesis: The main hypothesis of this proposal is that a socket, designed using the novel 
computational design framework, is equivalent to, or better than, a conventional socket (designed by 
a prosthetist) in terms of: 1) skin contact pressures, 2) gait symmetry, 3) walking metabolic cost, 4) 
skin irritation levels as assessed by the dermatologist, and 5) comfort as evaluated from a 
questionnaire. Our hypothesis is supported by the presented pilot data which shows reduced or 
equivalent skin contact pressures and subject reported comfort levels for several critical anatomical 
regions. 
Specifc Aims: 1) Subject-specifc biomechanical modeling for N=18 subjects, 2) Computational design 
and fabrication of sockets for N=18 subjects, and 3) Clinical evaluation of novel sockets for N=18 
subjects.
III.
STUDY POPULATION 
Sample Size 
A total of 18 subjects will be recruited for this study. The worst ratio between the mean and standard 
deviation for pilot contact pressure measurements for static standing was observed for the mid 
posterior wall, which presented with a mean of 97 kPa, and standard deviation of 8.9 kPa. If two-
tailed t-test based analysis is assumed, aiming to detect at least a 10% diference with respect to this 
mean, with a signifcance level of 0.05 and a power of 90%, the theoretically required number of test 
subjects is 12 (power analysis based on the MATLAB sampsizepwr function). However, to increase the 
chances of signifcant statistics for all measures (with varying signal to noise ratios), while also 
anticipating potential candidate drop-out, inclusion of N=18 subjects is proposed here. 
Statistical  analysis  of  the  socket  clinical  evaluation  data  will  focus  on  the  following 
measurements: 1) local skin contact pressures, 2) metabolic power, 3) gait parameters (symmetry 
indices for joint angles, positions, torques, and also ground reaction forces), and 4) the socket 
evaluation questionnaire. For scalar comparisons a paired t-test, with the level of signifcance set at 
0.05, will be used to test for diferences between the novel and conventional sockets. For time-series 
analysis of variance (ANOVA) will be used. 
Inclusion and exclusion criteria
18 healthy participants with below-knee amputations will be recruited. Participants will be generally 
healthy and will have no other musculoskeletal problems or any known cardiovascular, pulmonary or 
neurological  disorders.  This  study  will  consider  subjects  of  all  sex/gender,  race,  and/or  ethnic 
orientation, provided that they conform to the inclusion criteria summarized below. We focus on 
healthy subjects who are unilateral or bilateral transtibial amputees, who are between 18-64 years 
old, have an activity level of at least K3 (a person with the ability or potential for ambulation with 
variable cadence, and to traverse most environmental barriers and may have vocational, therapeutic 
or  exercise  activity  that  demands  prosthetic  use  beyond  simple  locomotion.)  and  that  their 
amputation took place more than 1 year prior to the start of the study. The latter is to exclude 
subjects whose limbs will undergo signifcant changes during the course of the study. Another 
inclusion criterion relates to the subject’s prosthetic sockets. In this study a comparison is made 
between a subject’s conventional sockets (designed by their experiences prosthetist) and our novel 
(computational modeling derived) sockets. Since we aim to match or improve upon comfortable 
prosthetic sockets, we will only include subjects whose current conventional sockets are deemed 
comfortable and of high quality. The quality of a subject’s conventional sockets will be judged by the 
consultant and certifed prosthetist involved in this study (Bob Emerson, A Step Ahead Prosthetics). 
One further inclusion criterion relates the subject’s ability to undergo MRI. If subjects are unable to 

undergo MRI (e.g. due to claustrophobia or the presence of objects their body that are not MRI Safe) 
they are excluded from this study. 
The American lower limb amputee population consists of subjects with varying etiology, sex, 
age, and ethnicity. Since clinical evaluation for only N=18 subjects is proposed here it is not practical 
to attempt to closely match all aspects of variation in the patient population. The key biological 
feature, relevant to the scientifc goals set out for this research, is the biomechanical behavior of soft 
tissue. The biomechanical behavior, e.g. soft tissue stifness dictates the response of the tissue to 
loading and therefore has a direct impact on socket comfort. The biomechanical behavior of soft 
tissue is known to vary with age, activity level and gender, but little information is known on efects 
of ethnicity on soft tissue biomechanics or amputee outcomes. Since variation in ethnicity is not 
expected to efect the study outcomes, subjects from all ethnicities may be eligible. Age and gender 
are more relevant for soft tissue biomechanics. We will aim to have our subject population refect the 
variation in the American amputee population in these respects.    
Subject recruitment
Subject recruitment (N=18) will be done via fyers, word of mouth, and by directly contacting subjects 
who have already worked with existing studies, or who are currently being seen by the consultant 
certifed  prosthetist  involved  in  this  study.  Furthermore,  we  will  actively  recruit  veterans  by 
advertising the study with the Boston chapter of the U.S. Department of Veteran Afairs. In order to 
participate in the study, eligible subjects will sign a consent form where pertinent information 
regarding the study will be provided to them.
IV.
STUDY DESIGN 
A cohort of 18 subjects will be recruited for this study. MRI data will be recorded for all subjects. 
Through image segmentation geometrically accurate 3D fnite element analysis (FEA) models will be 
constructed. Further, non-invasive indentation testing will be performed which, through combination 
with inverse FEA, provides accurate subject-specifc mechanical properties for all subjects. The 
resulting predictive FEA models will then be used in a novel, data-driven, and automated 
computational design framework for prosthetic sockets, to design prosthetic sockets for all subjects. 
The framework optimizes the socket designs, as assessed by skin contact pressures and internal 
tissue strain, through iterative adjustment of the virtual tests sockets. Final designs are subsequently 
3D printed. To evaluate the prosthetic sockets with each of the subjects each subject will do a 
standing and walking exercise using their conventional sockets or the novel sockets. Meanwhile skin 
contact forces, walking metabolic cost, and gait symmetry are recorded. After the exercises, skin 
irritation will be assessed by a dermatologist, and socket comfort is assessed using a questionnaire. 
Together this data provides a quantitative and qualitative evaluation and comparison of the novel 
and conventional sockets. 
V.
Methoastu 
The overall goal of this study is to further develop, and clinically assess, a computational and data-
driven design and manufacturing framework for mechanical interfaces that quantitatively produces 
transtibial prosthetic sockets in a faster and more cost-efective way compared with conventional 
processes.

In pursuit of our long-term goal, our team has recently developed a framework for prosthetic 
socket design and fabrication that involves: 1) non-invasive imaging to record patient geometry, 2) 
indentation to assess tissue mechanical properties, 3) data-driven and automated creation of patient-
specifc designs, 4) patient-specifc fnite element analysis and design evaluation, and 5) 3D printing 
of the end design for clinical evaluation. This study aims to advance these approaches, and clinically 
assess the overall design process for N=18 transtibial amputees. Socket evaluations are conducted 
during standing and walking activities. For these evaluations, skin-socket interface pressures are 
recorded using sensors located at the skin-socket interface. During the walking evaluation, motion 
capture is used additionally to allow for gait analysis. Furthermore, metabolic cost is measured by 
indirect calorimetry using an open circuit respirometry system. These experiments are repeated for 
each patient’s conventional socket for comparison. In addition to these quantitative evaluations, 
each study participant completes a socket evaluation questionnaire, and a certifed dermatologist 
writes a report documenting skin conditions subsequent to each socket test. 
The main hypothesis of this proposal is that the novel quantitative socket is equivalent to, or 
better than, a conventional socket in terms of: 1) skin contact pressures, 2) gait symmetry, 3) walking 
metabolic cost, 4) skin irritation levels as assessed by the dermatologist, and 5) comfort as evaluated 
from  a  questionnaire.  Furthermore,  we  hypothesize  that  equivalence  or  improved  socket 
performance can be achieved for all N=18 subjects using a single computational design framework, 
i.e. that we can formulate the computational design framework such that it can automatically design 
these sockets for all subjects without requiring algorithm adjustments from one subject to the next. 
In order to address the hypothesis that the novel sockets can perform equivalently to, or 
better than, conventional sockets (designed by a qualifed prosthetist) we propose an experimental 
evaluation using N=18 subjects. Static standing and walking exercises will be performed. During the 
standing and walking exercise skin contact pressures will be recorded. During walking skin contact 
pressure,  metabolic  cost,  and  motion  capture  data  will  be  recorded.  Finally,  a  custom  socket 
evaluation questionnaire will be used to assess the level of socket comfort experienced by the 
subject. 
This study consists of three phases: 
1) Data collection 
2) Socket design 
3) Socket evaluation
Participant involvement is required for phase 1 and 3 which occur in two separate sessions.
Session 1 (phase 1): Data collection
In the frst session, each amputee participant will be scheduled to visit the Biomechatronics Group in 
The MIT Media Laboratory and our imaging center (the MIT McGovern Institute). The main purpose of 
this session is to quantitatively measure the stifness of the residual limb and map out the anatomy 
of the residual limb,  for N=18 subjects,  by using  Magnetic Resonance Imaging (MRI), 3D scanner, 
ultrasound  scanner,  and  a  stifness-measuring  device  on  the  amputee.  Mechanical  property 
investigation may also take place during imaging, e.g. during MRI by using MRI compatible indentor 
systems. Subjects are scanned using a 3T MRI system (Siemens Magnetom 3 Tesla, Siemens Medical 
Systems, Erlangen, Germany). The structural and geometrical data derived from MRI (e.g. using 
segmentation) provides the input for computational model development (used in the socket design 
process).  Morphological  data  (such  as  height,  weight,  limb  length  and  circumference)  of  the 
participant will also be recorded. 

Session 2 (phase 3): Socket evaluation. 
During a second session the sockets (designed based on the image and mechanical property data) are 
evaluated  (at  the  MIT  Media  Lab’s  Biomechatronics  department).  In  this  session  both  the 
conventional  and  novel  socket  systems  will  be  tested.  For  all  subjects  the  order  of  testing 
(conventional or novel frst) is randomized. Subjects are frst asked to sit on a chair and expose their 
residual limb surface for force sensor placement. Recently we established a new inter-socket skin 
contact pressure assessment system based on fexible pressure and force sensors (A201, 111N, 
FlexiForce®, TekScan, Boston, MA, USA, and also F-Socket, TekScan, Boston, MA, USA). Data for an 
array of force sensors can be simultaneously recorded during static standing or dynamic walking 
exercises. Evaluating loads at select anatomical regions are of interest, these sites include: 1) the 
medial crest, 2) the fbular head, 3) the tibial crest, and 4) the Mid posterior wall. Sensors are secured 
to the skin using a thin adhesive tape (12.7 mm wide, 0.0625 mm thick, Scotch Magic®, 3M, USA) 
which can be removed with minimal discomfort. After sensor placement a liner is rolled over the skin 
and sensors. The conventional sockets are evaluated with the subject’s own liner and suspension 
system. For evaluation with the novel socket, subjects are ftted with a custom liner (e.g. through 
Ottobock Healthcare Gmbh) or standard commercially available liners (such as the Silosheath Double 
cushion 3-mm liner, Silipos Holding LLC, Niagara Falls, N.Y, USA). A commercially available sleeve is 
used for suspension (such as BK Suspension sleeve, Silipos Holding LLC, Niagara Falls, N.Y, USA). Next 
the compliant socket and rigid outer socket are donned on. For the novel sockets the outer socket is 
frst attached to the subject’s conventional foot-ankle system, and alignment is optimized by a 
certifed prosthetists (present during all socket ftting and evaluation procedures) consulted for this 
study (Bob Emerson, A Step Ahead Prosthetics). Once subjects have been ftted with the sockets the 
standing, followed by the walking exercise is conducted. For the walking exercise not only force but 
also metabolic cost and motion capture data are recorded. The metabolic analysis will provide an 
assessment of the energy expenditure while wearing either a conventional or the novel socket 
(discomfort may result in a less efcient or asymmetric gait causing increased energy use). For 
metabolic cost analysis, subjects are equipped with a breath-by-breath portable telemetric system 
(Model K4b2, COSMED, Rome, Italy). Subjects are also equipped with 46 refective markers (15 mm 
diameter) for motion capture (following the Helen Hayes marker model). For the standing evaluation 
subjects are asked to stand still in an upright position for 5 minutes while skin contact force (or 
pressure) data and resting state metabolic data is acquired. 
For the walking evaluation subjects are asked to walk at 1.4 m/s for 10 minutes on an 
instrumented treadmill (Bertec, Columbus, OH) while ground reaction forces are recorded, as well as 
3D marker locations and the metabolic data. The marker locations are recorded at a sampling rate of 
100 Hz by a 12 infrared camera motion capture system (model: T40s, Vicon Motion Systems Ltd, 
Oxford, UK). The locations of these markers is chosen to track joint motion. 
The treadmill system used for the walking exercise is equipped with parallel bars to prevent 
any injury to the subject if he were to lose balance and fall. A safely harness attached to the ceiling 
will also be utilized if the subject makes that request. In addition, a member of the laboratory staf 
will also accompany the study participant to catch him/her in the event of a fall, if necessary. The 
participant may ask to rest or to terminate their participation in the study at any time. The socket 
evaluation session (walking and standing evaluations) should take no more than 4 hours to complete. 
The kinematic  and  force  plate data can  be combined with inverse  dynamics  analysis  to 
compute joint angles and moment profles. Furthermore, analysis between data for the left and right 
limb and for the conventional and novel socket  allows for comparison of symmetry measures. 
Symmetry indices will be derived for: 1) ankle, knee, and hip joint angle, position, torque time 
profles, and 2) the vertical ground reaction forces. The metabolic measurements for standing will be 

subtracted from the metabolic rate of walking trials in order to obtain the net metabolic cost of 
walking. 
After the standing and walking exercises subjects will be requested to take of the socket and 
liner to expose their residual limb skin surface. The consultant dermatologist (Dr. Tan) will then 
inspect the skin and report on skin irritation. The dermatologist will also talk to the subjects on 
comfort and instruct them to fll out the developed socket evaluation questionnaire. Questions will 
also relate to points where contact pressure measurements will be made, thus enabling direct 
comparison of local comfort assessment to pressure fndings. Subjects fll out their answers by 
drawing a line at a desired level for each of the questions. This method allows for post-processing 
based conversion of the input to numerical data (i.e. 0-100 %) and lacks biases associated with 
constrained integer number input (e.g. favoring of even/odd numbers). 
Data & Safety Monitoring Plan
All sensor (e.g. force/pressure) data is recorded using data acquisition units (e.g. Arduino Uno, Arduino 
LLC) connected to dedicated laptop computers. The motion capture data (VICON system) and treadmill 
data (speed and force plates) are recorded using a dedicated desktop computer. The metabolic cost 
analysis are recorded on a dedicated data acquisition unit (COSMED) and are subsequently uploaded to 
a laptop computer. 
We  will  record  video  (in  digital  format)  for  each  subject  walking  for  analysis  and  development 
purposes. Videos in digital format will be archived in a password protected secure server located at the 
MIT Media Laboratory. Access to video material will be limited to authorized investigators associated 
with this study. Video will remain archived in the data server for future reference. Upon subject 
request, videos can be deleted from server once study is completed.
Benefits
There are no immediate benefts for participating in this study. The prosthetic sockets produced will 
be prototypes and would not be immediately available. 
It is expected that knowledge generated in this study will beneft society. The processes developed 
for producing 3D printed sockets during this research will be used to understand how to most 
efectively attach (mechanical) devices to humans. This understanding will aid the development of 
advanced prostheses, orthoses and other augmentation/rehabilitation technologies.
Risks 
Following the inclusion criteria (which include MRI safety) there should be no elevated risk associated 
with the MRI  acquisitions. Other risks and discomforts are minimal as they are those incurred by 
standing still for 5 minutes, and walking on a treadmill for 10 minutes, both while using either a 
conventional socket and the 3D printed socket. 
There will be a "spotter" standing next to the treadmill and close to the amputee while standing or 
walking in our facilities. We will give subjects periodic rest/water breaks. Any other necessary 
assistance to make the subjects comfortable will be provided. If during the standing or walking 
exercise the subject experiences discomfort such that he/she wishes to terminate the test he/she can 
decide to do so at any time. To minimize these uncomfortable situations, we will have a certifed 
prosthetist and a dermatologist around during the ftting process during the socket evaluation. 
The dermatologist (Dr. Tan) involved in the study will be present during socket evaluation and will 
judge skin irritation as a function of socket discomfort. Actual harm is unlikely but the researchers, 

dermatologist, and prosthetist are present to judge any potential harm. Feedback from the subject 
can be obtained promptly by researchers present, prosthetist, and/or the dermatologist present. The 
MIT ethical board (COUHES) will be informed of any adverse circumstances. No follow-up will be 
made as the procedure poses minimal risk of injury.  
Informed Consent
Informed consent will be obtained.  The informed consent process will be conducted prior to the 
initial visit by qualifed and approved study personnel. Retention is based upon the decision of each 
participant to continue with research enrollment. Participants may discontinue at any time without 
consequence.

VI.
DATA ANALYSIS 
Perstuonal iaentifierstu
All data and fles particular to a subject will be anonymized (subjects will be assigned a code for naming 
fles e.g. subject1mmonthmdaymyear) and stored on password protected computers to which only the 
members of the research group have access. 
Data stutorage
The data will be stored on a password protected computer server in the MIT  Biomechatronics Group, 
Media Laboratory, E-14 room 274.  Access to this server is secured by a password. Only authorized 
investigators associated with the study will have access to data.
Treatment of aata after stutuay completion
The data will remain in the MIT Media Laboratory secure server for future processing. Upon subject 
request, digital videos can deleted from the data server once study is completed.

VII.
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