Passive engineering mechanism enhancement of a flexor digitorum longus tendon transfer procedure.

Standard treatments of adult acquired flatfoot deformity (AAFD) fail to correct associated dysfunction of the posterior tibial tendon (PTT). This study aimed to determine if a novel passive engineering mechanism (PEM) enhanced flexor digitorum longus (FDL) tendon transfer procedure would better restore physiologic PTT function to improve AAFD gait parameters compared to standard treatment. We evaluated the kinetic, pedobarographic, and kinematic effects of a pulley-based PEM-enhancement system utilizing a cadaveric flatfoot model and robotic gait simulator. FDL tendon force, FDL tendon excursion, regional peak plantar pressures, center of pressure, and foot bone/joint motions were quantified. Throughout the stance phase of gait, PEM-enhancement significantly increased FDL tendon forces, resulting in gait cycle medial column unloading, lateral column loading, forefoot adduction, hindfoot inversion, and increased plantar flexion (p < 0.05). This proof-of-concept study demonstrated that an innovative PEM-enhanced FDL tendon transfer procedure better restored physiologic PTT function, resulting in improved correction of the distinctive AAFD gait characteristics-medial column collapse, hindfoot eversion, and forefoot abduction. Clinical significance: Novel PEM-enhancement of a FDL tendon transfer procedure holds promise as a method for improved treatment of AAFD. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3033-3042, 2018.