Effects of a Torsion-Adaptive Energy-Storing-and-Return Prosthetic Foot on Balance Control in Individuals with Transtibial Amputation: A Pilot Pre–Post Motion Analysis Study

Individuals with transtibial amputation have impaired postural control due to limited ankle function. Conventional energy-storing-and-return (ESAR) prosthetic feet mainly support sagittal-plane mechanics and provide limited frontal-plane adaptability. This pilot pre–post motion analysis study examined the effects of the Intersection Foot® (IF), a torsion-adaptive ESAR prosthetic foot, on balance control in 10 male individuals with unilateral transtibial amputation. Three-dimensional motion analysis and force plate measurements were performed during five Berg Balance Scale-derived tasks. During sit-to-stand, IF reduced the mediolateral root mean square distance of center of pressure from 10.20 ± 3.59 to 8.29 ± 3.32 mm (p = 0.047) and the anteroposterior center of mass (CoM) range from 345.51 ± 31.72 to 326.45 ± 47.40 mm (p = 0.008). During tandem stance, IF increased mediolateral CoM range from 23.94 ± 18.77 to 55.99 ± 30.90 mm (p = 0.021), vertical CoM range from 4.14 ± 4.18 to 9.45 ± 7.72 mm (p = 0.038), and sound-side frontal-plane ankle ROM from 1.44 ± 1.20° to 2.48 ± 1.30° (p = 0.022). Overall, replacing the habitual feet with IF produced task-dependent biomechanical adaptations rather than uniform improvements in postural stability, suggesting reduced dynamic sway during sit-to-stand but increased whole-body and sound-limb compensatory motion during tandem stance.