Tat Jimmy, Kociolek Aaron M, Keir Peter J
Department of Medicine, McGill University, Montreal, QC, Canada.
School of Physical and Health Education, Nipissing University, North Bay, ON, Canada.
J Biomech. 2016 Nov 7;49(15):3682-3687. doi: 10.1016/j.jbiomech.2016.09.038. Epub 2016 Oct 6.
The most common finding in carpal tunnel syndrome is fibrosis and thickening of the subsynovial connective tissue (SSCT). While the SSCT mediates tendon gliding in the carpal tunnel, this histopathology suggests excessive shear forces are involved in injury development. Ultrasound is often used to quantify relative motion between the finger flexor tendons and SSCT as an indirect measure of "shear-strain"; however, the underlying mechanical implications of using ultrasound are not well understood. The middle flexor digitorum superficialis (FDS) tendon of 8 cadavers was moved in a combination of 2 wrist postures (neutral, flexed), 3 velocities (5, 10, 15cm/s), and 3 forces (10, 20, 30N) to assess ultrasound-based FDS-SSCT relative displacement while simultaneously quantifying tendon frictional work in the carpal tunnel. We found independent velocity effects for both constructs (relative displacement, η=0.862, p<0.05; frictional work, η=0.937, p<0.05), indicating ultrasound captured viscous gliding resistance owing to the gel-like inter-fibrillar matrix of the SSCT. FDS-SSCT relative displacement also increased independently in a flexed wrist posture (p=0.010) and with greater tendon force (p=0.036), likely representing strain dependant changes with tendon position. Alternatively, we found a significant posture×force interaction on tendon frictional work (p<0.01), due to, in part, greater surface friction against the transverse carpal ligament with a flexed wrist and high force. While ultrasound provided a different interpretation compared to direct measurement of mechanical shear, FDS-SSCT relative displacement successfully localized viscoelastic shear-strain, which may help elucidate the role of hand motion in SSCT pathology and CTS.
腕管综合征最常见的表现是滑膜下结缔组织（SSCT）纤维化和增厚。虽然SSCT在腕管中介导肌腱滑动，但这种组织病理学表明，过度的剪切力参与了损伤的发展。超声通常用于量化手指屈肌腱与SSCT之间的相对运动，作为“剪切应变”的间接测量；然而，使用超声的潜在力学意义尚未得到很好的理解。对8具尸体的中指浅屈肌腱（FDS）在2种腕部姿势（中立、屈曲）、3种速度（5、10、15厘米/秒）和3种力（10、20、30牛）的组合下进行移动，以评估基于超声的FDS-SSCT相对位移，同时量化腕管中的肌腱摩擦功。我们发现两种结构都有独立的速度效应（相对位移，η=0.862，p<0.05；摩擦功，η=0.937，p<0.05），这表明超声捕捉到了由于SSCT的凝胶状纤维间基质而产生的粘性滑动阻力。FDS-SSCT相对位移在腕部屈曲姿势下（p=0.010）和肌腱力增大时（p=0.036）也独立增加，这可能代表了随肌腱位置的应变依赖性变化。另外，我们发现姿势×力对肌腱摩擦功有显著的相互作用（p<0.01），部分原因是腕部屈曲和高力时与腕横韧带的表面摩擦力更大。虽然与直接测量机械剪切相比，超声提供了不同的解释，但FDS-SSCT相对位移成功地定位了粘弹性剪切应变，这可能有助于阐明手部运动在SSCT病理学和腕管综合征中的作用。
