Direct visualization and measurement of the plantar aponeurosis behavior in foot arch deformation via the windlass mechanism

Abstract

The plantar aponeurosis (PA) is an elastic longitudinal band that contributes to the generation of a propulsive force in the push-off phase during walking and running through the windlass mechanism. However, the dynamic behavior of the PA remains unclear owing to the lack of direct measurement of the strain it generates. Therefore, this study aimed to visualize and quantify the PA behavior during two distinct foot postures: (i) neutral posture and (ii) windlass posture with midtarsal joint plantarflexion and metatarsophalangeal joint dorsiflexion, using computed tomography scans. Six healthy adult males participated in the experiment, and three-dimensional reconstruction of the PA was conducted to calculate its path length, width, thickness, and cross-sectional area. This study successfully visualized and quantified the morphological changes in the PA induced by the windlass mechanism, providing a precise reference for biomechanical modeling. This study also highlighted the interindividual variability in the PA morphology and stretching patterns. Although the windlass posture was not identical to that observed in the push-off phase during walking, the observed PA behavior provides valuable insights into its mechanics and potential implications for foot disorders.

Keywords: biomechanics; computed tomography; foot; kinematics; models; plantar.

FIGURE 1

CT‐scanned foot postures. Neutral (A) and windlass (B) postures. The windlass posture is a simulated weight‐bearing posture with metatarsophalangeal joint DF and midtarsal joint PF using a calf stretcher. DF, dorsiflexion; PF, plantarflexion.

FIGURE 2

Segmentation of the proximal (i), middle (ii), and distal (iii) portions of the plantar aponeurosis (PA) on the CT images resliced perpendicular to the PA path.

FIGURE 3

Definition of the origin (${\mathbf{p}}_{\mathit{\text{or}}}$), branch point (${\mathbf{p}}_{\mathit{br}\_i}$), via point (${\mathbf{p}}_{\mathit{via}\_i}$), point below the metatarsal head (${\mathbf{p}}_{\mathit{MH}\_i}$), and insertion (${\mathbf{p}}_{\mathit{ins}\_i}$) to calculate the lengths of the proximal ($L_{\mathit{\text{prox}}\_i}$) and distal ($L_{\mathit{\text{dist}}\_i}$) parts of the ith PA. PA, plantar aponeurosis.

FIGURE 4

Three‐dimensional model of the plantar aponeurosis (PA). Sagittal and frontal views in the neutral (A) and windlass (B) postures. Comparisons of the PA paths between two postures when the position and orientation of the calcaneus were aligned between the neutral (red) and windlass (yellow) postures (C).

FIGURE 5

Comparisons of the lengths of the PA between the neutral and windlass postures (A) and the strain of the PA when in the windlass posture (B). Mean (solid line with circle plots = neutral, dashed line with triangle plots = windlass) ± standard deviation (red and yellow bands, respectively) * p < 0.05. ** p < 0.01. PA, plantar aponeurosis.

FIGURE 6

Comparisons of the thickness, width, and cross‐sectional area of the PA measured at the proximal 10%, middle 50%, and distal 90% of the length of the proximal band ($L_{\mathit{\text{prox}}}$), between the neutral and windlass postures (A), and among different locations when in the neutral posture (B). Mean (solid line with circle plots) ± standard deviation (red band). * p < 0.05. ** p < 0.01. ⁺ p < 0.05. ⁺⁺ p < 0.01.

FIGURE 7

Length of the proximal part of the PA in the neutral (solid line with circle plots) and windlass (dashed line with triangle plots) postures. PA, plantar aponeurosis.