Comparative biomechanics and pathology of mammalian feet

足部疾病如关节炎、肌腱炎、骨髓炎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，由于动物残疾和安乐死，全球经济成本巨大。脚和地面之间的机械相互作用是一个关键因素。它还影响肥胖、虚弱和运动，从而使机械条件恶化。特别是，当脚在运动过程中撞击地面时的高频振动，以及随后在步骤中施加的大的力（因此应力或压力）是主要的原因或影响。然而，足部解剖结构差异巨大。马有一个极端的设计，一个脚趾结束在一个刚性的蹄，这是一流的快速摆动，但非常僵硬。当这种坚硬的蹄子撞击地面时，它会产生很大的振动，这些振动会导致组织损伤的逐渐积累。足部相对于身体来说是如此之小，以至于内部应力可能高度集中。相比之下，大象代表了另一个极端：它们的脚有五个脚趾，被束缚在一个由脂肪纤维组织组成的柔性垫（数字垫）中，这个垫很重，因此摆动起来很昂贵，但似乎很结实，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。这种足部设计是不是一种控制巨型动物高频冲击和压力的绝妙解决方案？那么，像猪蹄这样的中间设计是如何工作的呢？令人惊讶的是，这些重要问题几乎被忽视了。我们建议研究5个物种（猪，马，牛，犀牛，大象）从80-3000公斤的质量，以测量足部解剖和身体大小如何影响足部负荷。我们将通过对运动及其与足部疾病的联系的3部分分析来做到这一点。首先，我们将使用运动捕捉相机和力平台来测量行走和慢速跑步（例如小跑）期间四肢和脚部的动态。这将使我们能够表征脚与地面的碰撞力学。通过描述影响如何在~ 100倍大小范围内变化，我们将量化脚是如何设计来控制影响的。我们假设，影响水平保持在接近恒定的水平，跨动物大小的脚专业化。这可能会激发新的设计假肢或动物围栏的拱形表面。其次，我们将“放大”单独的脚的力学，使用3D高速运动捕捉和区域压力测量来确定外部脚在运动过程中如何变形，以及这些变形如何与局部压力相关。接下来，我们将使用尸体脚的体外加载和3D荧光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扫描来构建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，以估计跑步过程中脚部骨骼和其他组织的峰值应力。我们假设，在不同的物种中，峰值骨应力保持在接近恒定的水平，以保持安全边际，避免受伤。然而，这种安全性很容易因损坏（例如振动）或力学改变（例如肥胖或虚弱）而丧失。第三，我们将对我们的研究物种及其家养动物的野生亲属进行广泛的调查，以量化足部的哪些特定区域倾向于发展足部疾病。我们假设动物在我们的模型和实验显示运动过程中压力最大的区域会有更多的疾病。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，并与临床应用密切相关，将建立一个新的基础，广泛造福健康和福利。

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.