Gait Assessment in the Transtibial Mercer Universal Prosthesis Designed with a “Neutral Alignment” Socket

Standardizing socket design and maintaining a default socket alignment in transtibial prostheses are innovations that aim to simplify fitting procedures and reduce prosthetic service costs, particularly in low-income countries. Objectives: This study evaluated the Mercer Universal Prosthesis (MUP) with a standardized “neutral alignment” against custom-made conventional prostheses (CVPs). Methods: Twenty transtibial amputees (n = 20) completed gait assessments using their CVP and immediately after fitting with an MUP. Temporal–spatial and sagittal plane kinematics (hip, knee, and ankle angles) were analyzed, along with a gait symmetry index. Results: the MUP group reported a significant difference between the prosthetic and the intact limb for both hip and knee kinematics (p < 0.05), but there was no change in the CVP group. When compared with the sound limb in the MUP group, post hoc analysis showed that both hip flexion and the hip range of motion (ROM) in the MUP limb significantly increased by 5.7° and 7.3° (p = 0.002 and p < 0.001, respectively). Spatial and temporal gait parameters were comparable between the MUP and CVP groups, and gait symmetry showed no significant differences. The CVP showed greater symmetry in terms of hip (19%, p = 0.012) and knee flexion (8%, p = 0.026) compared to the MUP, while the MUP had higher plantarflexion symmetry (24.4%, p = 0.013). Conclusions: Immediately post fitting, MUP improved joint mobility in the prosthetic limb, potentially enhancing kinematics. While short-term benefits are evident, further research is needed to assess long-term gait adaptation and quality of life impacts.