Comparison of transhumeral socket designs utilizing patient assessment and in vivo skeletal and socket motion tracking: a case study

Assessing 3D printable density-graded lattice structures to minimize risk of tissue damage from compression-release stabilized sockets

BACKGROUND

Pressure, shear stress, and friction can contribute to soft tissue damage experienced by a residual limb. Current compression/release stabilized (CRS) socket designs may pose a risk to soft tissue from abrupt compression differences within the socket.Objectives:Density-graded lattice structures are investigated for their potential to mitigate risk of tissue damage by assessing their ability to produce more gradual transitions between high-compression and low-compression areas.Study Design:A full factorial experimental design was used to reveal the effects of changes among three variables: lattice geometry, density alteration, and displacement magnitude. A total of 144 experimental conditions were examined.

METHODS

Lattice samples representing areas of compression and release based on a novel cushioned transhumeral level CRS style socket design were 3D printed. Compression testing was performed on 2 types of lattice structures which incorporated 1 of 8 design elements to alter density and axial stiffness. The effect on stiffness of the sample as a function of lattice type and density alteration was recorded under 3 loading conditions.

RESULTS

The offset diamond lattice type with blend radius density alterations produced the only samples meeting criteria set for compression areas of the socket. No samples satisfied criteria for release areas. Transitional density lattices that gradually tapered between the best performing compression and release values were successfully produced.

CONCLUSIONS

Transitional density lattices offer promise for mitigation of soft tissue damage through minimization of compression differentials throughout the socket. Wider implications for this research include use in sockets for other levels of amputation and in orthotics. Future work will focus on lattice optimization to improve release behavior within a modified CRS socket.

Measuring residual limb health in persons with upper limb amputation: Modifications of the Prosthetic Evaluation Questionnaire residual limb health scale

BACKGROUND

Assessing the user perspective on residual limb health problems is particularly important for amputation care, given the relationship between residual limb health and prosthetic satisfaction. Only 1 measure, the Residual Limb Health scale of the Prosthetic Evaluation Questionnaire (PEQ) has been validated for use in lower limb amputation, but not examined in persons with upper limb amputation (ULA).

OBJECTIVES

The objective of this study was to examine the psychometric properties of a modified PEQ Residual Limb Health scale in a sample of persons with ULA.

STUDY DESIGN

The study involved a telephone survey of 392 prosthesis users with ULA, with a 40-person retest sample.

METHODS

The PEQ item response scale was modified to a Likert scale. The item set and instructions were refined in cognitive and pilot testing. Descriptive analyses characterized the prevalence of residual limb issues. Factor analyses and Rasch analyses evaluated unidimensionality, monotonicity, item fit, differential item functioning, and reliability. Test-retest reliability was assessed by an intraclass correlation coefficient.

RESULTS

Sweating and prosthesis odor were prevalent at 90.7% and 72.5%, respectively; blisters/sores (12.1%) and ingrown hairs (7.7%) were the least prevalent problems. Response categories were dichotomized for 3 items and trichotomized for 3 items to improve monotonicity. After adjusting for residual correlations, confirmatory factor analyses showed acceptable fit (comparative fit index = 0.984, Tucker-Lewis index = 0.970, and root mean square error approximation = 0.032). Person reliability was 0.65. No items had moderate-to-severe differential item functioning by age or sex. Intraclass correlation coefficient for test-retest reliability was 0.87 (95% CI, 0.76-0.93).

CONCLUSIONS

The modified scale had excellent structural validity, fair person reliability, very good test-retest reliability, and no floor or ceiling effects. The scale is recommended for use with persons with wrist disarticulation, transradial amputation, elbow disarticulation, and above-elbow amputation.

Effects of Prosthetic Socket Design on Residual Femur Motion Using Dynamic Stereo X-Ray - A Preliminary Analysis

Individuals with transfemoral amputation experience relative motion between their residual limb and prosthetic socket, which can cause inefficient dynamic load transmission and secondary comorbidities that limit mobility. Accurately measuring the relative position and orientation of the residual limb relative to the prosthetic socket during dynamic activities can provide great insight into the complex mechanics of the socket/limb interface. Five participants with transfemoral amputation were recruited for this study. All participants had a well-fitting, ischial containment socket and were also fit with a compression/release stabilization socket. Participants underwent an 8-wk, randomized crossover trial to compare differences between socket types. Dynamic stereo x-ray was used to quantify three-dimensional residual bone kinematics relative to the prosthetic socket during treadmill walking at self-selected speed. Comfort, satisfaction, and utility were also assessed. There were no significant differences in relative femur kinematics between socket types in the three rotational degrees of freedom, as well as anterior-posterior and medial-lateral translation (p > 0.05). The ischial containment socket demonstrated significantly less proximal-distal translation (pistoning) of the femur compared to the compression/release stabilization socket during the gait cycle (p < 0.05), suggesting that the compression/release stabilization socket provided less control of the residual femur during distal translation. No significant differences in comfort and utility were found between socket types (p > 0.05). The quantitative, dynamic analytical tools used in the study were sensitive to distinguish differences in three-dimensional residual femur motion between two socket types, which can serve as a platform for future comparative effectiveness studies of socket technology.

An adaptive socket with auto-adjusting air bladders for interfacing transhumeral prosthesis: A pilot study

Comfort is a critical aspect in the application of wearable device, such as rehabilitation robots and upper limb prostheses. As a physical interface between human body and prosthetic limb, the socket and its comfort largely contribute to the user's acceptance. Traditional sockets are static, lacking dynamic adjustment mechanism for the contact pressure. To ensure a reliable suspension during daily activities, the socket is usually designed to be tightly attached, with a large stress, on the residual limb, which may introduce considerable discomfort during long-term use. In this article, we present a novel adaptive transhumeral socket, in which we employ four independent bladders contacting with the stump. Not only can these bladders provide a necessary suspension for the device but also form an air cushion (soft body) that helps relieve the pressure concentration between the biological body and physical prosthesis. In real time, this adaptive socket continuously monitors the limb posture, the operating load, and the contacting pressure between the socket and the limb, and then dynamically adjusts the clamping force to ensure a reliable attachment during various daily activities. Since well adapting to the contours of the stump, the bladders can effectively accommodate the volume change of the stump, making a balanced load distribution on load-tolerant areas. Through modeling and numerical analysis, we established a dynamic strategy for estimating the external load and an automatic scheme for adjusting the bladders' air pressure. Finally, a close-loop control was constructed based on the contact pressure measured by our self-developed force sensors. Our preliminary experiments on one normal (i.e. non-amputee) subject verified the effectiveness of the proposed method, showing that the adaptive socket can considerably reduce the socket-limb contact pressure while sustaining a secure suspension on the upper arm.

Characterization of interfacial socket pressure in transhumeral prostheses: A case series

One of the most important factors in successful upper limb prostheses is the socket design. Sockets must be individually fabricated to arrive at a geometry that suits the user's morphology and appropriately distributes the pressures associated with prosthetic use across the residual limb. In higher levels of amputation, such as transhumeral, this challenge is amplified as prosthetic weight and the physical demands placed on the residual limb are heightened. Yet, in the upper limb, socket fabrication is largely driven by heuristic practices. An analytical understanding of the interactions between the socket and residual limb is absent in literature. This work describes techniques, adapted from lower limb prosthetic research, to empirically characterize the pressure distribution occurring between the residual limb and well-fit transhumeral prosthetic sockets. A case series analyzing the result of four participants with transhumeral amputation is presented. A Tekscan VersaTek pressure measurement system and FaroArm Edge coordinate measurement machine were employed to capture socket-residual limb interface pressures and geometrically register these values to the anatomy of participants. Participants performed two static poses with their prosthesis under two separate loading conditions. Surface pressure maps were constructed from the data, highlighting pressure distribution patterns, anatomical locations bearing maximum pressure, and the relative pressure magnitudes. Pressure distribution patterns demonstrated unique characteristics across the four participants that could be traced to individual socket design considerations. This work presents a technique that implements commercially available tools to quantitatively characterize upper limb socket-residual limb interactions. This is a fundamental first step toward improved socket designs developed through informed, analytically-based design tools.