Measuring and Predicting Soft Tissue Strains following Lower Limb Amputation

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

Lower limb amputation is a life-altering event that may significantly impact an individual's independence, social situation and quality of life. The major rehabilitation obstacle is discomfort in loading the residual limb, and the risk of soft tissue injury. A personalised socket allows the transmission of loads generated during activities of daily living, from the prosthetic limb into the musculoskeletal system. Sockets are designed by skilled prosthetists, who use iterative trial sockets to reach a final socket. This is a real challenge as the residual limb changes size throughout the day with temperature, activity and hydration, and adapts over time. Amputees must return to their prosthetist several times in the first year, at considerable expense and inconvenience. There is a clear clinical need for an improved, quantitative basis for prosthetic socket design and fabrication, and an understanding of how stump-socket fit influences long-term rehabilitation outcomes. This is the objective of our research programme.

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 01/10/2016 30/09/2021
1831892 Studentship EP/N509747/1 09/01/2017 31/12/2019 Jennifer Bramley
 
Description Post-amputation, reformed soft tissues of the residual limb, that have not been mechanically conditioned to support load, represent a vulnerable site with high potential for tissue damage. These soft tissues form a critical interface with a prosthetic socket, transferring load during activities of daily living. This inevitably creates pressure at the skin-device interface, which can result in recurring soft tissue discomfort and damage.
The aim of this research was to assess tissue tolerance at the residual limb-prosthesis interface.
This was to be achieved by applying representative pressure to the right calf of 10 participants without amputation and both lower limbs of 10 participants with unilateral transtibial amputation, via an inflatable cuff. Measurements were taken at the skin surface to record the response and MRI was used to observe how the limbs changed shape under load and how soft tissue composition changed post-amputation.

Measurements demonstrated that low representative loads were sufficient to affect vascular activity and cause deformation of the soft tissues.This research used the calf tissue of participants without amputation as a control representative of the newly reformed soft tissues of the residual limb as neither will have been mechanically conditioned to support load. Participants with a range of cause of amputation and time since amputation were recruited to further understanding of tissue adaptation post-amputation. Results demonstrated lower ischaemic and inflammatory responses at some residual limb sites indicating greater tolerance to loading potentially due to prosthetic load bearing. This work highlights the importance and consideration of duration wearing prosthetic devices particularly in the early stages of rehabilitation. There is a potential for tissue damage can occur at low representative pressures. Ischaemic and inflammatory precursors to tissue damage can be measured at low representative loads to assess tissue tolerance to loading.
Exploitation Route The measurement array could be implemented in a larger cohort of participants with amputation to further understand soft tissue adaptation and tolerance post-amputation and how to translate measurement techniques for daily and clinical use.
Sectors Healthcare
 
Description These data will contribute to understanding of safe tissue loading thresholds for early rehabilitation and prosthesis use, reducing the risk of tissue damage and improving quality of life for prosthesis users. Investigation of these measurement techniques will help to inform clinically implementable techniques that could be used in everyday life to reduce the risk of tissue damage.
Sector Healthcare
 
Title Measurement Array to Characterise Biomechanical and Physiological Effects on Dermal Tissues of Simulated Prosthetic Loading on a Cohort of Participants with Unilateral Transtibial Amputation 
Description A human in-vivo protocol has been developed for assessing the biomechanical and physiological response of lower limb soft tissues to loads representative of prosthesis use during early rehabilitation when using the Pneumatic Post-Amputation Mobility Aid. Pressure was applied incrementally from 20 to 60 mmHg to their lower limb tissues using a pressure cuff. An array of measurements, taken at three sites relevant to prosthetic load bearing, included: - Magnetic Resonance Imaging to characterise direct tissue deformation; - Myoton measurement of structural tissue stiffness; - Transcutaneous oxygen (TcPO2) and carbon dioxide (TcPCO2) measurement to characterise ischaemia; and - Collection of biomarkers, further exploring their potential as precursors to tissue damage. 
Type Of Material Physiological assessment or outcome measure 
Year Produced 2019 
Provided To Others? Yes  
Impact Techniques showed potential to enable measurement of precursors to tissue damage at the residual limb-prosthetic socket interface. Results enabled further understanding of adaptation and behaviour of soft tissues following lower limb amputation. The measurement array was presented at the 17th ISPO World Congress in 2019 recorded in the publications section. 
 
Title Measurement Array to Characterise Physiological Effects on Dermal Tissues Following Simulated Prosthetic Loading on a Cohort of Participants Without Amputation 
Description A human in-vivo protocol has been developed for assessing the biomechanical and physiological response of lower limb soft tissues to loads representative of prosthesis use during early rehabilitation when using the Pneumatic Post-Amputation Mobility Aid. Pressure was applied incrementally from 20 to 60 mmHg to their lower limb tissues using a pressure cuff. An array of measurements, taken at three sites relevant to prosthetic load bearing, included: - Magnetic Resonance Imaging to characterise direct tissue deformation; - Transcutaneous oxygen (TcPO2) and carbon dioxide (TcPCO2) measurement to characterise ischaemia; - Visualisation of lymphatic activity using near Infra-Red imaging; and - Collection of biomarkers, further exploring their potential as precursors to tissue damage. 
Type Of Material Physiological assessment or outcome measure 
Year Produced 2018 
Provided To Others? Yes  
Impact Techniques showed potential to enable measurement of precursors to tissue damage at the residual limb-prosthetic socket interface. This research is still ongoing and the array of measurement techniques, excluding visualisation of lymphatic activity, has now been translated for prosthesis users, to enhance knowledge of biomechanical adaptation and behaviour of soft tissues following lower limb amputation. The measurement array has been presented at a number of conferences recorded in the publications section. 
 
Description Demonstration of 3D printing in University open workshop for undergraduate students 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact A weekly open 3D printing workshop is available for students to come and receive help in 3D printing for their design projects. 3D printing has been used within this research to manufacture MRI safe testing equipment and I regularly demonstrate at the workshop, helping students to print 3D print and discussing research projects. I have also presented at introductory 3D printing lectures in the workshop.
Year(s) Of Engagement Activity 2017,2018,2019,2020
 
Description SmallPeice Bioengieering Design Project Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact The Smallpeice Trust organises a yearly one week visit to the University of Southampton for secondary school students, who have just finished their GCSE's, to carry out STEM projects for a week and learn about Bioengineering to try and inspire them and show them what careers are available. I ran a keyhole surgery design project where three teams of students designed keyhole surgery implements to perform surgery on a plaster cast torso and score points by completing tasks such as removing plasticine bugs. The students were interested in finding out more about bioengineering and the projects that are carried out at the University of Southampton.
Year(s) Of Engagement Activity 2018,2019