# A biofidelic mock residual limb for prosthetic socket testing

## TL;DR

A low-cost, adjustable mock residual limb was developed to test prosthetic sockets, enabling repeatable and controllable volume changes for better device prototyping.

## Contribution

A biofidelic mock limb with real-time volume adjustment and high repeatability for prosthetic socket testing was designed and validated.

## Key findings

- The mock limb can adjust volume by ±5% and maintains consistent interfacial pressure regardless of change rate.
- The design is repeatable with a pressure coefficient of variation below 10.4% across three tests.
- The limb is cost-effective and customizable for simulating different residual limb physiologies.

## Abstract

Evaluating prosthetic socket fit and function relies on accurately simulating load transfer between the residual limb and the socket. This limb can be either real (of a study participant) or a mock residual limb that simulates in vivo properties. Mock limbs minimize reliance on resource-intensive clinical trials; however, most are static in size, limiting their use in testing clinical outcomes like socket adjustability.

To design and validate a biofidelic mock limb, capable of real-time, controllable volume adjustments of up to ±5% limb volume.

Water-filled bladders were embedded within a transtibial residual limb model made of a dual-durometer urethane composition, mimicking deep and soft tissue. An Arduino-controlled syringe system was used to actuate volume adjustments. The method was validated through repeatability tests at different rates of volume change, cycling through expansion, holding at maximum volume, and contraction. Volume change was quantified by measuring interfacial pressures between the limb and a static socket.

The limb was fabricated with readily available materials for less than CAD 400. Volume change rate had minimal effect on interfacial pressure throughout the testing cycle, and minimal hysteresis was found between expansion and contraction periods. Repeatability was high, with a coefficient of variation of normalized pressure remaining below 10.4% over three repeated tests.

The proposed biofidelic limb was validated for its ability to mimic volume change in a transtibial residual limb. The design enables easy replication or customization to simulate different limb physiologies and anatomies. The limb allows for controllable bench-top testing during prototyping of adjustable sockets or other devices, thus bringing devices to clinical use sooner.