Quantitatively-informed Socket Design Process

Study Overview
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Brief Summary
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This study will investigate the effects of specific standardized modifications to trans-femoral prosthetic sockets in a randomized within-subject design. This is in preparation for a subsequently planned clinical trial to validate the findings by implementing them into a fitting method for individual sockets.

Detailed Description
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Background: Lower limb amputees experience chronic health challenges such as residual limb skin problems, low back pain, and osteoarthritis. These problems are exacerbated by high physical activity levels and by poor prosthetic socket fit. Prosthetists believe that limiting residual femur and skin motion will improve force coupling and thereby address these problems. However, there are no data demonstrating how changes in socket design affect residual femur and skin motion, and, by extension, lead to improved patient-reported outcomes. Objective/Hypothesis: Goal of this research is to improve the current socket design optimization process that involves trial and error and relies heavily on the prosthetist's experience and intuition by using a quantitatively informed optimization process. The hypothesis is that modifiable in-socket mechanics, i.e. residual femur motion, skin strain, and pressure within the socket, are related to socket design and patient outcomes, and can be estimated using readily available clinical measurements. Specific Aims: First aim is to identify the key characteristics of in-socket mechanics that are related to physical function and patient-reported comfort and function. The second aim is to identify readily available clinical measurements that are associated with the in-socket mechanical characteristics that are related to outcomes. The purpose of this aim is to correlate our laboratory findings from Aim 1 with more conventional modalities for clinical assessment. Research Strategy: Preliminary data demonstrates the feasibility of the proposed research plan and will progress to a pilot clinical trial. The two aims will involve 30 transfemoral amputees. A highspeed biplane radiography system is used to image the residual limb while participants walk on a dual-belt instrumented treadmill both in their current socket and in sockets with purposely altered volume, brim height, cross-sectional geometry, and stiffness. Three-dimensional (3D) skin motion within the socket will be determined by tracking the motion of 40 to 50 small metal beads placed in a grid pattern on the skin of the residual limb before donning the socket. Residual femur motion within the socket will be determined with submillimeter accuracy using a validated tracking process that matches subject-specific bone models obtained from CT to the biplane radiographs. Discrete in-socket pressure will be recorded at four locations using pressure sensing pads. Readily available clinical measurements will be collected as well, including gait analysis, foot loading patterns, ground reaction forces, residual limb tissue stiffness, and hip range of motion hip strength. Each participant will complete clinical questionnaires to qualitatively evaluate comfort, fit, and overall satisfaction after wearing each socket. The different socket modifications are intended to affect the in-socket mechanics of the residual limb, physical function and patient-reported outcomes (Aim 1). These relationships will be assessed using a generalized linear model. Correlation between the research grade measurements and accessible clinical measures (Aim 2) will be evaluated using bivariate correlation analyses. The information gained in Aims 1 and 2 will be used to develop a quantitatively-informed socket optimization process, wherein the clinical measurements associated with in-socket mechanics will be used to inform socket design optimizations.

Official Title
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Improving Physical Function and Patient-reported Outcomes Through a Quantitatively-informed Socket Design Process

Conditions
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Artificial Limbs

Intervention / Treatment
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* Device: Trans-femoral prosthetic socket


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Transfemoral prosthesis user 18-80 years of age Body weight less than 125 kg Able to walk unassisted on a treadmill Exclusion Criteria: Pregnant females Clinically diagnosed osteoporosis Previous high exposure to radiation

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 80 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Intervention Model: Single Group Assignment
Interventional Model Description: Participants will perform study activities with nine different versions (including the original unmodified) of their prosthetic socket in a randomized sequence.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Unmodified Socket + 8 Socket Modifications in Random Order<br>The sequence of the 9 different interventions (original socket and 8 versions derived from it) is randomized for each participant. The number of participants is smaller than the number of possible permutations. Therefore the enacted ordering is randomly selected from the pool of possible orderings. Participants walk for less than 10 minutes with every socket type while data is being collected. | Device: Trans-femoral prosthetic socket<br>* Unmodified) A custom-made check socket serving as the interface between residual limb and prosthesis Soft socket (Socket made from softer material than unmodified original) Stiff socket (Socket made from stiffer material than unmodified original) moderately lower brim height (Brim of the socket is lowered by 10% of socket length compared to unmodified original) slightly lower brim height (Brim of the socket is lowered by 5% of socket length compared to unmodified original) Oversized socket (The socket volume is 6% larger than the unmodified original) Undersized socket (The socket volume is 6% smaller than the unmodified original) CAT-CAM influenced geometry (The cross sectional geometry of the socket is modelled following the contoured adducted trochanteric-controlled alignment method (CAT-CAM)) MAS influenced geometry (The cross sectional geometry of the socket is modelled following the Marlo Anatomic Socket (MAS) template)<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Residual Femur motion | medial-lateral and superior-inferior translation of the distal femur relative to the socket from late swing through midstance | 1 second | 
| Skin strain | average and peak skin strain within each of four regions, expressed as a percentage of the gait cycle | 1 second | 
| Socket pressure | measure peak pressure and area under the pressure versus time curve, expressed as a percentage of the gait cycle | 20 seconds | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Gait symmetry | average of the peak trunk lean, and the average peak hip flexion and extension, measured by motion capture system | 20 seconds | 
| Plantar pressure | peak plantar pressure from foot strike to midstance | 20 seconds | 
| Static displacement | distance from the most distal point of the residual femur to the inside surface of the socket under weightbearing | 1 second | 
| Tissue Stiffness | Average tissue stiffness for four regions of the residual limb | 3 seconds | 
| Trunk lean | Body angles based on markers placed on the shoulders and spine | 20 seconds | 
| Hip flexion/extension | Based on markers at greater trochanters, knee, ankle and foot. | 20 seconds | 
| Hip strength | Manual muscle testing of hip flexors and extensors | 20 seconds | 
| Hip Range of Motion | Manually measured using goniometer | 20 seconds |