No Association of Plantar Aponeurosis Stiffness with Medial Longitudinal Arch Stiffness

Quantification of the in vivo stiffness and natural length of the human plantar aponeurosis during quiet standing using ultrasound elastography

This study aimed to identify the stiffness and natural length of the human plantar aponeurosis (PA) during quiet standing using ultrasound shear wave elastography. The shear wave velocity (SWV) of the PA in young healthy males and females (10 participants each) was measured by placing a probe in a hole in the floor plate. The change in the SWV with the passive dorsiflexion of the metatarsophalangeal (MP) joint was measured. The Young's modulus of the PA was estimated to be 64.7 ± 9.4 kPa, which exponentially increased with MP joint dorsiflexion. The PA was estimated to have the natural length when the MP joint was plantarflexed by 13.8°, indicating that the PA is stretched by arch compression during standing. However, the present study demonstrated that the estimated stiffness for the natural length in quiet standing was significantly larger than that in the unloaded condition, revealing that the PA during standing is stiffened by elongation and through the possible activation of intrinsic muscles. Such quantitative information possibly contributes to the detailed biomechanical modeling of the human foot, facilitating an improved understanding of the mechanical functions and pathogenetic mechanisms of the PA during movements.

Effects of Barefoot and Shod on the In Vivo Kinematics of Medial Longitudinal Arch During Running Based on a High-Speed Dual Fluoroscopic Imaging System

Shoes affect the biomechanical properties of the medial longitudinal arch (MLA) and further influence the foot’s overall function. Most previous studies on the MLA were based on traditional skin-marker motion capture, and the observation of real foot motion inside the shoes is difficult. Thus, the effect of shoe parameters on the natural MLA movement during running remains in question. Therefore, this study aimed to investigate the differences in the MLA’s kinematics between shod and barefoot running by using a high-speed dual fluoroscopic imaging system (DFIS). Fifteen healthy habitual rearfoot runners were recruited. All participants ran at a speed of 3 m/s ± 5% along with an elevated runway in barefoot and shod conditions. High-speed DFIS was used to acquire the radiographic images of MLA movements in the whole stance phase, and the kinematics of the MLA were calculated. Paired sample t-tests were used to compare the kinematic characteristics of the MLA during the stance phase between shod and barefoot conditions. Compared with barefoot, shoe-wearing showed significant changes (p < 0.05) as follows: 1) the first metatarsal moved with less lateral direction at 80%, less anterior translation at 20%, and less superiority at 10–70% of the stance phase; 2) the first metatarsal moved with less inversion amounting to 20–60%, less dorsiflexion at 0–10% of the stance phase; 3) the inversion/eversion range of motion (ROM) of the first metatarsal relative to calcaneus was reduced; 4) the MLA angles at 0–70% of the stance phase were reduced; 5) the maximum MLA angle and MLA angle ROM were reduced in the shod condition. Based on high-speed DFIS, the above results indicated that shoe-wearing limited the movement of MLA, especially reducing the MLA angles, suggesting that shoes restricted the compression and recoil of the MLA, which further affected the spring-like function of the MLA.