Influence of neglecting the curved path of the Achilles tendon on Achilles tendon length change at various ranges of motion

Abstract

Achilles tendon length has been measured using a straight‐line model. However, this model is associated with a greater measurement error compared with a curved‐line model. Therefore, we examined the influence of neglecting the curved path of the Achilles tendon on its length change at various ranges of motion. Ten male subjects participated in this study. First, the location of the Achilles tendon was confirmed by using ultrasonography, and markers were attached on the skin over the Achilles tendon path. Then, the three‐dimensional coordinates of each marker at dorsiflexion (DF) 15°, plantarflexion (PF) 0°, PF15°, and PF30° were obtained. Achilles tendon length in the curved‐line model was calculated as the sum of the distances among each marker. On the other hand, Achilles tendon length in the straight‐line model was calculated as the straight distance between the two most proximal and distal markers projected onto the sagittal plane. The difference of the Achilles tendon length change between curved‐line and straight‐line models was calculated by subtracting the Achilles tendon length change obtained in curved‐line model from that obtained in straight‐line model with three different ranges of motion (i.e., PF0°, PF15°, and PF30° from DF15°, respectively). As a result, the difference in Achilles tendon length change between the two models increased significantly as the range of motion increased. In conclusion, neglecting the curved path of the Achilles tendon induces substantial overestimation of its length change when the extent of ankle joint angle change is large.

Effects of Contract–Relax, Static Stretching, and Isometric Contractions on Muscle–Tendon Mechanics

“…However, a possible limitation of this method is that linear 3D motion analysis model using 2 reflective markers was used to calculate Achilles tendon length. A curved path using multiple reflective markers may more accurately reflect Achilles tendon length (11), with substantial error introduced when measurements are taken over multiple, joint angles. However, error using the linear model is negligible in the anatomical position (0.8%; ref 11), thus any error in tendon length is likely minimal in the present study.…”

Quantifying mechanical loading and elastic strain energy of the human Achilles tendon during walking and running

“…Previous in vivo approaches used for assessing AT length during functional tasks either calculated AT length using a simple planimetric model 7 , 8 or did not consider the AT's concave curvature in their measurements 1 , 25 , 26 . There is evidence that considering the AT as a straight line between calcaneus (insertion) and gastrocnemius medialis (GM) myotendinous junction (MTJ, origin) results in an underestimation of the AT length and substantial errors (up to 78%) of the AT length changes 27 .…”

“…Although this method has been validated by comparing the outcomes with accurate AT length measurements from magnetic resonance imaging 30 , it has not been applied to assess AT length during locomotion. The neglect of AT's curvature during locomotion could result in a 3.4 mm error when the ankle rotates from 30° in plantar flexion to 15° in dorsiflexion 27 . Considering an average AT rest length of 200 mm would cause a significant strain error of 1.7%.…”

Automatic Myotendinous Junction Tracking in Ultrasound Images with Phase-Based Segmentation

“…As an illumination and contrast invariant measure of symmetric structures, phase congruency can be employed to perceive and enhance ridge-like features [ 34 ], which is beneficial for the detection of tendinous tissues using Radon transform. Moreover, MTJ is the specific site of connection between tendons and muscles [ 54 ], which can be identified as the intersection of two aponeuroses in ultrasound images [ 55 , 56 ]. With the consideration of the poor localization of phase-based techniques, the locations and the orientation of tendinous tissues and MTJ were used to facilitate the segmentation of MTJ obtained with LRT and Otsu methods.…”

“…Furthermore, a two-point representation may not properly account for the Achilles tendon curvature. The Achilles tendon is almost straight in the dorsiflexion region; as the ankle joint angle changes, the Achilles tendon becomes slightly curved, resulting in an approximately 3% underestimation of tendon length with the plantar flexion angle reaching 30° [ 55 ]. Thus, this effect is likely to be a minor factor in measuring MTJ and tendon length in daily human movements.…”