Department of Radiology, University of Wisconsin-Madison, Madison, WI, USA; Department of Medical Physics, University of Wisconsin-Madison, Madison, WI, USA.
Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI, USA.
J Biomech. 2014 Aug 22;47(11):2685-92. doi: 10.1016/j.jbiomech.2014.05.008. Epub 2014 May 16.
Supersonic shear imaging (SSI) is an ultrasound imaging modality that can provide insight into tissue mechanics by measuring shear wave propagation speed, a property that depends on tissue elasticity. SSI has previously been used to characterize the increase in Achilles tendon shear wave speed that occurs with loading, an effect attributable to the strain-stiffening behavior of the tissue. However, little is known about how shear wave speed varies spatially, which is important, given the anatomical variation that occurs between the calcaneus insertion and the gastrocnemius musculotendon junction. The purpose of this study was to investigate spatial variations in shear wave speed along medial and lateral paths of the Achilles tendon for three different ankle postures: resting ankle angle (R, i.e. neutral), plantarflexed (P; R - 15°), and dorsiflexed (D; R+15°). We observed significant spatial and posture variations in tendon shear wave speed in ten healthy young adults. Shear wave speeds in the Achilles free tendon averaged 12 ± 1.2m/s in a resting position, but decreased to 7.2 ± 1.8m/s with passive plantarflexion. Distal tendon shear wave speeds often reached the maximum tracking limit (16.3m/s) of the system when the ankle was in the passively dorsiflexed posture (+15° from R). At a fixed posture, shear wave speeds decreased significantly from the free tendon to the gastrocnemius musculotendon junction, with slightly higher speeds measured on the medial side than on the lateral side. Shear wave speeds were only weakly correlated with the thickness and depth of the tendon, suggesting that the distal-to-proximal variations may reflect greater compliance in the aponeurosis relative to the free tendon. The results highlight the importance of considering both limb posture and transducer positioning when using SSI for biomechanical and clinical assessments of the Achilles tendon.
超声剪切波成像（SSI）是一种超声成像方式，通过测量剪切波传播速度来提供组织力学的洞察力，该速度取决于组织弹性。SSI 先前已被用于描述跟腱的剪切波速度随加载而增加，这归因于组织的应变硬化行为。然而，关于剪切波速度如何在空间上变化知之甚少，这很重要，因为跟骨插入部和腓肠肌腱-肌腹连接处之间存在解剖学差异。本研究的目的是在三个不同的踝关节姿势（休息踝关节角度（R，即中立）、跖屈（P；R-15°）和背屈（D；R+15°））下，研究跟腱内侧和外侧路径的剪切波速度的空间变化。我们观察到十名健康年轻成年人的跟腱的剪切波速度存在显著的空间和姿势变化。在休息位置，跟腱自由部分的剪切波速度平均为 12 ± 1.2m/s，但在被动跖屈时降至 7.2 ± 1.8m/s。当踝关节处于被动背屈姿势（从 R 增加 15°）时，远端跟腱的剪切波速度通常达到系统的最大跟踪限制（16.3m/s）。在固定姿势下，从自由腱到腓肠肌腱-肌腹连接处的剪切波速度显著降低，内侧测量的速度略高于外侧。剪切波速度与跟腱的厚度和深度仅呈弱相关，这表明从远端到近端的变化可能反映了相对于自由腱，跟腱的腱膜的顺应性更大。结果强调了在使用 SSI 进行跟腱的生物力学和临床评估时，考虑肢体姿势和换能器定位的重要性。
