Poster Q9 - GAIT ASSESSMENT IN THE TRANSTIBIAL MERCER UNIVERSAL PROSTHESIS WITH “NEUTRAL ALIGNMENT”

Introduction: In fitting Transtibial protheses, clinicians iteratively adjust the Dynamic alignment (DA) of the prosthesis with respect to the residual limb in an attempt to achieve gait symmetry for the amputee’s sound and prosthetic limbs1,2. In clinical practice, however, achieving gait symmetry through DA is often compromised to prioritize the patient’s socket comfort. The process of achieving DA is time-consuming and cost-intensive, imposing a significant financial burden on the approximately 2.1 million amputees residing in North America. Despite the clinical efforts to optimize DA for gait symmetry, studies on Transtibial gait with socket DAs have not shown a significant change within the clinically accepted 10-degree tolerance3.
If DA remains unchanged within this tolerance, adopting a standard alignment might benefit the current and future 150,000 new amputees in North America annually, eliminating the need for the DA process. The concept of standard alignment is exemplified in the Mercer Universal Prosthesis (MUP®) design (US patent # 8870968). The low-cost MUP® incorporates a standard “neutral alignment” that aims to maintain axial alignment between the hip, knee and prosthesis ankle joints, eliminating the need for DA in tuning the patient’s gait. The objective of this study is to quantitatively compare the gait characteristics of Transtibial amputees wearing conventional custom-made and MUP® prostheses. It was hypothesized that spatial and kinematic gait parameters would differ between the sound limb and prosthetic limb within transtibial amputees wearing conventional custom-made (Old) and MUP® prostheses.

Materials and

Methods: 20 Vietnamese transtibial amputees (19 male, 1 female, aged 59.96 ±7.09 years) walked overground at self-selected speed in two conditions: i) using pre-existing (Old) custom prosthetic devices with “bench alignment” (5 degrees of socket flexion and adduction ) and SACH foot design, and ii) immediately after fitting a MUP® prosthesis to replace their Old prosthesis. 3D Gait Analysis was conducted using Ultium® Portable Lab (Noraxon Inc., USA), including lower limb IMU motion sensors (200 Hz) and in-shoe pressure sensors (500 Hz).
Figure 1: Vietnamese amputee wearing the conventional custom-made Old prostheses (Left) and the MUP® prostheses (Right)
Gait kinematics was quantified using maximum, minimum, and total ranges of motion in bilateral sagittal joint angles (hip, knee, ankle), peak plantar pressure in stance phase, and spatial COP parameters (i.e. A/P and Lateral position and gait line). MATLAB® was used to compute intrasubject mean data across approximately 5 strides, and a two-factor repeated measures ANOVA (p < 0.05) tested main effects and interactions between devices (Old vs. MUP) and limbs (Sound vs. Prosthetic). Post hoc pairwise t-tests were used if there was a significant interaction between the devices (comparing limbs for each device, and comparing devices for each limb). Statistical analysis was performed on SPSS (Version 22, IBM, USA ).

Results, Conclusions, and Discussions: Gait analysis revealed asymmetry between sound and prosthetic limbs, with prolonged stance phase in the sound limb and shortened swing phase in the prosthetic limb1,2 in both Old and MUP. However, no significant differences of the spatial parameters were found between the two devices . Additionally, gait symmetry assessment, based on the COP for both limbs, did not demonstrate significant A/P and lateral symmetry between the sound and prosthetic limbs in both MUP and Old devices.
Table 1: Summary of COP Symmetry (N=14 is due to missing data)
For sagittal joint angle analysis, a significant limb-device interaction emerged from the two-factor ANOVA. Post hoc analysis revealed an increase in Hip total ROM (p=0.036), maximum Hip extension (p=0.031), and maximum Knee flexion (p=0.55) during the stance for the MUP prosthetic vs. Old prosthetic, but not for the sound limbs (MUP and Old prostheses).
Figure 2: Sagittal Hip and Knee Angles between MUP and Old
Immediately after fitting the MUP device, participants’ COP and kinematic gait parameters were qualitatively similar those observed when using their Old prostheses. However, increases in hip extension and knee flexion angles could indicate improved gait symmetry with the MUP prosthesis. Future work should analyze longitudinal performance and comfort when using the MUP device.

Acknowledgements (Optional): This study was funded by the Mercer On Mission Office