Changes in Tissue Composition and Load Response After Transtibial Amputation Indicate Biomechanical Adaptation

J L Bramley,D L Bader,P R Worsley,A Darekar,A S Dickinson,L King,C Everitt

doi:10.1007/s10439-021-02858-0

J L Bramley, D L Bader + Show 5 more

Open Access

https://doi.org/10.1007/s10439-021-02858-0

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Abstract

Despite the potential for biomechanical conditioning with prosthetic use, the soft tissues of residual limbs following lower-limb amputation are vulnerable to damage. Imaging studies revealing morphological changes in these soft tissues have not distinguished between superficial and intramuscular adipose distribution, despite the recognition that intramuscular fat levels indicate reduced tolerance to mechanical loading. Furthermore, it is unclear how these changes may alter tissue tone and stiffness, which are key features in prosthetic socket design. This study was designed to compare the morphology and biomechanical response of limb tissues to mechanical loading in individuals with and without transtibial amputation, using magnetic resonance imaging in combination with tissue structural stiffness. The results revealed higher adipose infiltrating muscle in residual limbs than in intact limbs (residual: median 2.5% (range 0.2–8.9%); contralateral: 1.7% (0.1–5.1%); control: 0.9% (0.4–1.3%)), indicating muscle atrophy and adaptation post-amputation. The intramuscular adipose content correlated negatively with daily socket use, although there was no association with time post-amputation. Residual limbs were significantly stiffer than intact limbs at the patellar tendon site, which plays a key role in load transfer across the limb-prosthesis interface. The tissue changes following amputation have relevance in the clinical understanding of prosthetic socket design variables and soft tissue damage risk in this vulnerable group.

Highlights

Following lower limb amputation, the residual skin and soft tissues form a critical interface with the bespoke ‘socket’ component of a prosthetic limb
Residual limbs were observed to have a smaller cross-sectional area and a less consistently round shape than intact limbs, the residual limbs often revealed distorted shape artefacts resulting from the foam support (Fig. 3)
A higher proportion of muscle-infiltrating adipose was observed in residual limbs compared to intact limbs, indicating muscle atrophy post-amputation

Summary

Introduction

The residual skin and soft tissues form a critical interface with the bespoke ‘socket’ component of a prosthetic limb. The tissue tolerance to loading magnitude and duration varies between individuals,[19] and is influenced by many intrinsic factors.[10] There has been relatively little research into skin damage in individuals with lower limb amputations, despite the specific risk factors and high prevalence in this group.[18] the residual limbs are exposed to challenging biomechanical conditions, impaired load tolerance due to comorbidities, considerable variability in anatomy and surgical reconstruction, and the presence of scar tissue over vulnerable sites.[41]

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