Quantifying Bone and Skin Movement in the Residual Limb-Socket Interface of Individuals with Transtibial Amputation Using Dynamic Stereo X-Ray

Individuals with lower extremity amputation (LEA) often experience relative motion between their residual limb and the prosthetic socket, such as vertical translation and axial rotation, which can cause inefficient dynamic load transmission from the distal prosthetic components to the residual limb. This can lead to

significant secondary consequences, such as pain, gait deviations, and discomfort that limit mobility and autonomy. Assessments of the relative motion between the bone and the prosthetic socket have been performed, but there is little existing data on dynamic, in vivo residual limb-socket kinematics since most investigations

have been performed using non-dynamic testing protocols, static measurements, or with unvalidated surface marker-based motion capture systems. Dynamic Stereo X-ray (DSX) is an advanced imaging technology that can quantify 3D bone movement and tissue/liner deformation inside a prosthetic socket during dynamic activities.

It can achieve sub-millimeter accuracy of bone pose (position and orientation) measurement during functional movements by combining 3D models derived from CT scans with movement data from biplanar x-ray video. There is a substantial gap in our understanding of the complex mechanics of the residual limb-socket

interface during dynamic activities that limit the ability to improve prosthetic design. Our 4-year goals for this project are to develop the analytical tools to quantify both the dynamic, in-vivo kinematics between the residual limb and socket, as well as the mechanism of residual tissue/liner deformation. In order to validate the sensitivity

of this methodology to differences in socket suspension, we will evaluate 2 suspension systems: elevated vacuum (EV) and simple suction. We hypothesize that an efficient and highly accurate method to quantify the dynamic interaction between the residual limb and prosthetic socket will be sensitive enough to distinguish between

different types of prosthetic socket suspension, which will further the biomechanical understanding of socket design. To do so, the investigators will address the following aims: (1) To optimize the DSX procedural setup for the accurate tracking of the prosthetic socket, skeletal kinematics, and tissue/liner deformation; (2) To quantify

the relative motion between the residual tibia and the prosthetic socket during dynamic activities; and (3) To measure the deformation of the skin and liner in the prosthetic socket during dynamic activities. To address these aims, we will first employ a cadaver study to optimize the placement of an array of radio-

opaque beads and markers on the socket, liner, and skin to simultaneously assess both dynamic skeletal movement and residual tissue/liner deformation. Five cadaver limbs will be utilized in an iterative process to develop an optimal marker setup. Stance phase gait will be simulated during each DSX session to induce bone

movement and skin/liner deformation. The number and placement of markers will be evaluated after each session to refine the marker placement to track skin/liner deformation and skeletal movement. Once an optimal marker setup is identified, 21 subjects with transtibial amputation will be fit with a socket capable of being

suspended via both EV and traditional suction. Subjects will undergo a 4-week acclimation period and then be tested at the DSX facility at Rutgers University. DSX will be utilized to track skeletal and skin/liner motion under both suspension techniques during 3 dynamic activities: treadmill walking at self-selected speed, fast walking

(10% faster), and a step-down movement. The performance of the two suspension techniques (active EV and normal suction) will be tested by quantifying the 3D bone movement of the residual tibia with respect to the prosthetic socket and quantifying liner and soft tissue deformation at the socket-residuum interface.

By using the analytical tools for a highly accurate, in-vivo assessment of residual limb-socket motion, we can provide vital foundational information to aid in the development of new methods and techniques to enhance prosthetic fit that have the potential to reduce secondary physical comorbidities and degenerative changes that

result from complications of poor prosthetic load transmission.