Insights into the spectrum of transtibial prosthetic socket design from expert clinicians and their digital records.

Background: Transtibial prosthetic sockets are often grouped into patella tendon bearing (PTB) or total surface bearing (TSB) designs, but many variations in rectifications are used to apply these principles to an individual's personalised socket. Prosthetists currently have little objective evidence to assist them as they make design choices. Aims: To compare rectifications made by experienced prosthetists across a range of patient demographics and limb shapes to improve understanding of socket design strategies. Methodology: 163 residual limb surface scans and corresponding CAD/CAM sockets were analysed for 134 randomly selected individuals in a UK prosthetics service. This included 142 PTB and 21 TSB designs. The limb and socket scans were compared to determine the location and size of rectifications. Rectifications were compiled for PTB and TSB designs, and associations between different rectification sizes were assessed using a variety of methods including linear regression, kernel density estimation (KDE) and a Naïve Bayes (NB) classification. Results: Differences in design features were apparent between PTB and TSB sockets, notably for paratibial carves, gross volume reduction and distal end elongation. However, socket designs varied across a spectrum, with most showing a hybrid of the PTB and TSB principles. Pairwise correlations were observed between the size of some rectifications (e.g., paratibial carves; fibular head build and gross volume reduction). Conversely, the patellar tendon carve depth was not associated significantly with any other rectification, indicating its relative design insensitivity. The Naïve Bayes classifier produced design patterns consistent with expert clinician practice. For example, subtle local rectifications were associated with a large volume reduction (i.e., a TSB-like design), whereas more substantial local rectifications (i.e., a PTB-like design) were associated with a low volume reduction. Clinical implications: This study demonstrates how we might learn from design records to support education and enhance evidence-based socket design. The method could be used to predict design features for newly presenting patients, based on categorisations of their limb shape and other demographics, implemented alongside expert clinical judgement as smart CAD/CAM design templates.

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

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.

Establishing a measurement array to assess tissue tolerance during loading representative of prosthetic use.

BACKGROUND: In the early stages of rehabilitation after primary amputation, residual limb soft tissues have not been mechanically conditioned to support load and are vulnerable to damage from prosthetic use. There is limited quantitative knowledge of skin and soft tissue response to prosthetic loading. METHODS: An in-vivo protocol was developed to establish suitable measures to assess tissue tolerance during loading representative of early prosthesis use. Ten participants without amputation one participant with trans-tibial amputation were recruited, and pressure applied to their calf in increments from 20 to 60 mmHg. Measurements were recorded at relevant skin sites including interface pressures, transcutaneous oxygen (TCPO2) and carbon dioxide (TCPCO2) tensions and inflammatory biomarkers. FINDINGS: At the maximum cuff pressure, mean interface pressures were between 66 and 74 mmHg, associated with decreased TCPO2 values. On the release of pressure, the ischaemic response was reversed. Significant upregulation (p < 0.05) in inflammatory biomarker IL-1α and its antagonist IL-1RA were observed at all sites immediately following loading. INTERPRETATION: The protocol was successful in applying representative prosthetic loads to lower limb tissues and monitoring the physiological response, both in terms of tissue ischemia and skin inflammation. Results indicated that the measurement approaches were sensitive to changes in interface conditions, offering a promising approach to monitor tissue status for people with amputation.