Comparative biomechanics and pathology of mammalian feet

关节炎、肌腱炎、骨髓炎等足部疾病和包括骨折在内的损伤是大多数圈养/家养动物的主要肌肉骨骼健康问题，由于动物残疾和被安乐死造成了巨大的全球经济损失。脚和地面之间的机械相互作用是一个关键因素。它还会影响肥胖、虚弱和运动，从而恶化机械状况。特别是，在运动过程中，当脚撞击地面时的高频振动，以及在后面的步骤中施加的大力（因此应力或压力），是主要的原因或影响。然而，足部解剖结构差异很大。马有一个极端的设计，一个脚趾末端是一个刚性的蹄子，这是极好的快速摇摆，但非常僵硬。当这个坚硬的蹄碰到地面时，它会产生巨大的振动，这些振动会导致组织损伤的逐渐累积。脚相对于身体来说太小了，内部压力可能会高度集中。相比之下，大象代表了另一种极端：它们的脚有五个脚趾被一层由脂肪纤维组织组成的柔软垫（数字垫子）束缚着，这种垫子很重，因此摆动起来很昂贵，但看起来很结实，似乎可以抑制“脚跟”撞击时的振动。其他大型哺乳动物也有类似的解剖结构。这种足部设计是一种神奇的解决方案，可以控制大型动物的高频冲击和压力吗？那么，像猪“蹄子”这样的中间设计是如何工作的呢？令人惊讶的是，这些重要的问题几乎被忽视了。我们拟研究5个物种（猪、马、牛、犀牛、大象），体重在80-3000公斤之间，以测量足部解剖和体型对足部负荷的影响。我们将对运动及其与足部疾病的联系进行三部分分析。首先，我们将使用动作捕捉相机和力平台来测量行走和慢跑（如小跑）期间四肢和脚的动态。这将使我们能够描述足部与地面碰撞的力学特性。通过描述冲击如何在100倍的尺寸范围内变化，我们将量化脚是如何设计来控制冲击的。我们假设，不同体型、不同脚部的动物受到的冲击水平保持在接近恒定的水平。这可能会启发人们设计新的足部假肢或动物围栏的缓冲表面。其次，我们将“放大”脚部的力学，使用3D高速运动捕捉和区域压力测量来确定外部脚部在运动过程中如何变形，以及这些变形与局部压力的关系。接下来，我们将使用体外加载尸体脚和3D透视视频来复制这种机械环境，以测量内部脚如何变形。最后，我们将使用CT和MRI扫描来建立这些脚的高度逼真的有限元模型，以及我们在体内和体外测量的力学，以估计跑步过程中骨骼和其他组织的峰值应力。我们假设，跨物种，峰值骨应力保持在接近恒定的水平，以保持安全边缘，避免受伤。然而，这种安全性很容易因损坏（如振动）或力学改变（如肥胖或虚弱）而丧失。第三，我们将对我们的研究物种及其野生家畜近亲进行广泛的调查，以量化脚的哪些特定区域容易发生足部疾病。我们假设，在我们的模型和实验显示运动过程中压力最大的区域，动物会有更多的疾病。这将激发新的足部疾病诊断和预防措施。我们新颖的方法多样性和强大的比较方法将产生对动物足部解剖学和力学奥秘的研究爆炸式增长，并与临床应用紧密联系，将为广泛造福健康和福利奠定新的基础。

Foot disorders such as arthritis, tendonitis, osteomyelitis and injuries including bone fractures are the major musculoskeletal health problem for most captive/domestic animals, with huge global economic costs due to disabled and euthanised animals. The mechanical interaction between the foot and the ground is a critical contributor. It also influences obesity, weakness, and exercise, which worsen mechanical conditions. In particular, high-frequency vibrations when the foot impacts the ground during locomotion, as well as large forces (hence stresses, or pressures) imposed later in the step, are major causes or influences. However, foot anatomy varies enormously. Horses have an extreme design with one toe ending in a rigid hoof, which is superb for fast-swinging but very stiff. When this rigid hoof hits the ground, it generates large vibrations, and these vibrations can cause gradual accumulation of tissue damage. The foot is so small relative to the body that internal stresses may be highly concentrated. In contrast, elephants represent another extreme: their feet have five toes bound in a flexible pad of fatty, fibrous tissue (the digital cushion), which is heavy and thus costly to swing, but seems strong and seems to dampen vibrations at 'heel' impact. Other large mammals have similar anatomies. Is this foot design thus a marvellous solution that controls high-frequency impacts and stresses in giant animals? How then do intermediate designs such as pig 'trotters' work? Such important questions surprisingly remain almost ignored. We propose to study 5 species (pigs, horses, cows, rhinos, elephants) from 80-3000 kg mass, to measure how foot anatomy and body size influence foot loading. We will do this with a 3-part analysis of locomotion and its links with foot disease. First, we will use motion capture cameras and force platforms to measure the dynamics of the limbs and feet during walking and slow running (e.g. trotting). This will enable us to characterize the mechanics of foot impact with the ground. By characterising how impacts change across a ~100x size range, we will quantify how feet are designed to control impacts. We hypothesise that impact levels are maintained at near-constant levels across animal sizes by foot specialisations. This may inspire new designs for foot prosthetics or cushioned surfaces for animal enclosures. Second, we will 'zoom in' on the mechanics of the feet alone, using 3D high-speed motion capture and regional pressure measurements to determine how the external foot deforms during locomotion and how those deformations relate to localised pressures. Next, we will replicate this mechanical environment using in vitro loading of cadaveric feet and 3D fluoroscopic video to measure how the internal foot deforms. Finally, we will use CT and MRI scans to build highly realistic Finite Element models of these feet and the mechanics we have measured in vivo and in vitro, to estimate the peak stresses in bones and other tissues of the feet during running. We hypothesise that across species, peak bone stresses are kept at near-constant levels to preserve margins of safety that avoid injury. This safety however can easily be lost by damage (e.g. by vibration) or altered mechanics, such as obesity or weakness. Third, we will conduct a broad survey of our study species, and their wild relatives for domestic animals, to quantify which specific regions of the feet tend to develop foot disorders. We hypothesise that animals will have more disease in regions where our models and experiments show the highest stresses during locomotion. This should inspire new diagnostic and preventative measures for foot disorders. Our novel diversity of methods and powerful comparative approach will generate an explosion of research into the mystery of animal foot anatomy and mechanics, and with its strong links to clinical applications will build a new foundation to broadly benefit health and welfare.