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New grant awarded by the BBSRC to Dr John Hutchinson, Dr Renate Weller (RVC) and Dr Lei Ren (King's College London) for £433,077 to work on Comparative Biomechanics and pathology of mammalian feet.

A new grant has been awarded to the Royal Veterinary College for £433,077 to look at unravelling the complex interaction between foot form, substrate properties/habitat, size, locomotor behaviour and biomechanics across a diversity of large quadrupedal mammals.

The most common cause of morbidity and mortality of large animals in captivity and domesticity is foot disease. Foot pathologies encountered clinically are similar across species, including humans, and encompass degenerative (e.g. osteoarthritis, tendonitis, laminitis), infectious (e.g. foot abscesses) and traumatic (e.g. fractures) disorders. Foot disease is often progressive and treatment unrewarding in many cases, thus resulting in a poor prognosis for many individuals. Prevention is therefore key in ensuring the welfare of those animals, and knowledge about the main factors contributing to the aetiopathogenesis of foot disease an essential prerequisite. The causes of these pathologies are multifactorial. But the biomechanical foot-ground interaction is a major factor, particularly the frequencies and amplitudes of loading at and after foot impact, which can exacerbate pathology even if not the primary cause.

Why do animal feet (manus and pes) vary so widely in their anatomy, even among herbivorous quadrupeds? Or in other words, what are the functional consequences of foot anatomical variation? Evolutionary history (e.g. ancestrally even-toed artiodactyls, odd-toed perissodactyls, and the five-toed foot inherited by the first mammals) surely has played a huge role in shaping foot form. But how are size and biomechanical function related to foot design? Our integrative study across species of different sizes and anatomies is the most promising approach to establish new general principles that link foot biomechanics and pathogenesis. To understand how feet work, we must determine the influences of loads (size/speed), behaviour, and evolutionary history.

Pathological elephant hindfoot
Severely osteoarthritic elephant's hindfoot in side view.

Aims of the project:

We seek to:

  • Characterise how limb-ground impacts scale with animal size and how they are compensated for by anatomical and behavioural strategies

  • Determine how the regional loads on foot structures (bones, joints, pads, ligaments and tendons) relate to the occurrence of pathologies

  • Elucidate the causal relationships between foot form, function and pathology.

We aim to take an important, fundamental first step for unravelling the complex interaction between foot form, substrate properties/habitat, size, locomotor behaviour and biomechanics across a diversity of large quadrupedal mammals. Regardless of whether our hypotheses are correct, we will gain vital new insight into the biomechanical constraints on foot form and function, and make progress toward formulation of general principles of foot construction and mechanics.

computer model of an elephant hindlimb3D musculoskeletal computer model of an elephant's hindlimb (in side view) used to estimate how the muscles and tendons, including those of the feet, support and move elephants.

Establishing causal links between animal size, foot anatomy, function and disease has vast economic and animal welfare implications in addition to its fundamental scientific importance. Foot related lameness in cows costs the UK dairy industry around £90,000,000 each year, and is the third most common reason for culling. The incidence of lameness has been put at 69 cases per 100 cows per year, thus posing a substantial economical as well as welfare issue.

Lameness has the highest annual incidence, the second longest duration and number of days lost to work in horses. In about 80% of cases, the lameness is localised to the foot. In most cases the animal suffers pain for an extended period of time and in many cases, the disease will progress, ultimately ending in loss of use of the animal and death on economic grounds. Elephants are one of the most popular species kept in zoos and circuses with approximately 16,500 Asian and 1,000 African elephants in captive settings worldwide3. Foot problems are one of the major causes of morbidity and mortality in captive elephants and in one retrospective study of 379 elephants, 50% were found to be affected by foot disease.

Our study is basic science but has clear and diverse benefits for many strategic aims/priorities:

  • Animal health: Lameness is a poorly understood syndrome that is the most common cause of euthanasia, and >80% of the pathology is located in the foot. Foot treatments rarely cure or prevent pathology. It is hence paramount to improve and invent treatments via a thorough understanding of foot mechanics.
  • Animal welfare: Foot pathologies are dominant causes of disability and euthanasia in kept animals. Natural foot form and function are far removed from domestic conditions. Our study will enhance understanding of foot mechanics and foot-ground interaction; thus improving animal husbandry; and illuminate how domesticity has altered natural foot form and function. It will help predict how much more weight (e.g. in draught animals) can be carried safely by different animals. Our simulations could predict the effects of orthotic intervention and thereby spin-off to commercial/medical applications.
  • Ageing: Many disorders that are common in the elderly affect the feet, e.g. osteoporosis, osteoarthritis and diabetes. Foot disorders increase the risk of falls and hence injuries. The resulting limitations on mobility cause secondary problems (e.g. obesity), accelerating the ageing process. Our study will help elucidate how ageing affects the feet in many species.
  • Arthritis: The foot encompasses many joints and (osteo)arthritis is commonly observed. Species have evolved locomotor strategies to keep joint stresses at safe levels and allow sufficient joint motion. Osteoarthritis is irreversible and often progressive despite treatment, hence prevention is key. Understanding the fundamental comparative principles of foot mechanics will help to optimise orthotic intervention and exercise protocols.
  • Obesity: Heavier individuals load their feet relatively more, elevating stresses. But how have large animals evolved to modulate these stresses? Quantification of these mechanisms will inspire new prevention measures.
  • Biomaterials: Feet are marvellously complex systems. We will determine how the interactions of foot material properties influence function across species. The foot provides an unique opportunity to determine the interaction between live biomaterials and inert surface substrates.
  • Theoretical biology: Scaling and computer modelling feature prominently in this study. Finite Element Analysis involves the non-invasive estimation of stresses in complex structures such as feet to quantify form-function relationships, and our study will advance these methods. Furthermore, this project would benefit theoreticians and roboticists modelling or designing physical feet, which are among the greatest challenges for successfully emulating locomotor function. Co-I Ren has published simplified rollover models for human feet; our work will enable similar models of foot shape to be created for animals, improving simulations of critical foot-ground interactions.
  • Systems approaches: Our integration of multiple scales of complexity from foot anatomy to limb mechanics and broad scaling trends is an exemplar of modern systems-level biomechanics. This approach promises to give the deepest insights into organismal function and pathology, and should inspire future holistic studies.
  • 3Rs: Our methods replace those requiring surgical implantations of devices that would (1) only give limited localized surface strain data, (2) cause discomfort and lead to unreliable results.

a pressure trace from an elephant hindfoot
A record of the vertical pressures underneath an elephant's hindfoot. "Hot" colours are high pressure; "cool" colours are low pressure. The white line illustrates the path that the foot's centre of pressure takes during a step. The toenails are on the right side of the image; the heel is on the left.

Researchers in health and welfare, biomechanics and physiology, comparative anatomy and evolution and many others will benefit as ours is the first integrative study of foot biomechanics in hoofed mammals, paving the way for an explosion of research. A better understanding of foot mechanics will assist palaeontologists and biologists in correlating foot morphologies with habitats and locomotor modes.

This project is a joint collaboration between the Royal Veterinary College and King's College London. Dr John Hutchinson (PI) is a Reader in Evolutionary Biomechanics at the Royal Veterinary College. Dr Renate Weller (Co-I) is a Lecturer and Clinician at the RVC. She has two PhDs, one in medical imaging and one in animal locator biomechanics. She has extensive experience in both clinical and research orientated imaging. Dr Lei Ren (Co-I) is based at King's College London. He has two PhDs, one in mechanical engineering and one in human locomotion biomechanics. He has extensive experience in applying physical, mathmatical and mechanical methods to biomechanics. Dr Olga Panagiotopoulou will join the team at the Royal Veterinary College as a postdoc, straight from her PhD work at Hull York Medical School. She is already an expert on finite element modelling and will augment her skills in skull/feeding biomechanics with a new repertoire in limb/locomotor biomechanics.

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