Background/Objectives: Ultrasound-guided flexor pollicis longus (FPL) injection is limited by the muscle’s deep location and its proximity to the cephalic vein (CV) and superficial branch of the radial nerve (SBRN). We aimed to identify the wrist and forearm posture producing the largest measured corridor width and target exposure. Methods: This prospective single-center study evaluated 51 forearms from 27 healthy adult volunteers with full range of motion, using transverse ultrasound of the distal volar forearm in six standardized positions. Two corridors were measured: CV-to-SBRN (L₁, Approach A) and CV-to-radial-cortex apex (L₂, Approach B), with FPL exposure height (F). Results: L₂ was present in all limbs and was wider with forearm supination than in neutral (supination [SUP], +2.36 mm; flexion plus supination [F+SUP], +2.05 mm; extension plus supination [E+SUP], +2.66 mm; each p < 0.001), an ~40% increase; the three supination postures did not differ. F increased across the same postures and was greatest in E+SUP (+2.32 mm), which did not differ from SUP. L₁ was absent in 12–28% of limbs and, where present, was narrower with supination (both p < 0.001). Conclusions: In healthy adults, forearm supination widened the safety corridor and increased target exposure. Applicability to spasticity requires confirmation.

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.