Computational Design, Fabrication, and Evaluation of Optimized Patient-Specific Transtibial Prosthetic Sockets

Title: Computational Design, Fabrication, and Evaluation of Optimized Patient-Specific
Transtibial Prosthetic Sockets

Principle investigator: Dr. Hugh Herr

Background: The overall goal of this application 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-effective 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
insufficiently employed. Furthermore, discomfort, skin problems and pressure ulcer formation
remain prevalent. Through the proposed computational modeling framework, a repeatable,
data-driven and patient-specific design process is made available which is based on
scientific 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.

Specific Aims: 1) Subject-specific 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.

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 finite
element analysis (FEA) models will be constructed. Further, non-invasive indentation testing
will be performed which, through combination with inverse FEA, provides accurate
subject-specific 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.

Inclusion Criteria:

- Age: 18-64 years old

- Amputation type: Transtibial amputation (bilateral or unilateral) which took place >1
year prior to study

- Activity or K-level: At least K3

- Socket quality: The subject's conventional socket(s) should be deemed of high quality
and comfortable

- MRI safety: Subjects should be able to undergo MRI

Exclusion Criteria: