**5.1 Lameness**

*Veterinary Anatomy and Physiology*

poiesis takes place in the bone marrow [37].

**5. Morphological changes and pathologies in the foot**

The external morphology of the hoof capsule is indirectly associated with the function and shape of the internal segments of the hoof [38]. Dyson and colleagues [39] drew attention to the fact that, despite differences in the orientation of the distal phalanx between horses, mainly associated with changes in direction of the dished solar border, the morphology of the distal phalanx is unaffected by the external features of the hoof capsule. It is worth noting here that hoof shape can be altered when trimming and shoeing are considered [40]. The impact of trimming/shoeing on the hoof capsule shape has been explained [41] and the researchers demonstrated that the formation of the hoof wall is physically connected to the loading of the lower limb, thus protecting its optimal balance on the ground [42]. Therefore, the geometrical tendency of the foot components determines the ability of the internal structures to respond to loading through the bearing phase of the stride cycle [43]. The distal phalanx is attached within the hoof capsule through the suspensory apparatus [44], which connects the entire parietal surface of the distal phalanx to the lamellar structures of the internal hoof wall [11]. Preliminary work on equine lamellar connection found that this attachment provides the mechanism by which the weight is transferred between the distal phalanx and the epidermal laminae of the hoof wall [45]. This connection, or attachment, has a substantial role in the biomechanics of healthy foot performance, and may lead to foot lameness if damaged [41]. Indeed, the failure of the connection between the epidermal laminae and the underlying basement membrane of the dermal lamellae would weaken the suspensory apparatus of the distal phalanx [46]. Unsurprisingly, changes in the basement membrane of the suspensory tissue have been suggested to signal the first step of laminar failure [47]. While other research reported that lesions in the basement membrane appear before any clinical signs of foot lameness [48]. The dislocation of the distal phalanx, followed by its rotation, applies pressure, first on the sole at the palmar border of the distal phalanx and, secondly, on the coronet or upper area of the lamellae by the extensor process of the distal phalanx [49]. These deflections lead to impaired blood flow into the basal layers of the hoof wall [18], and can lead

Bone also acts as reservoir for growth factors and cytokines, which are released during bone resorption and take effect either locally or systemically [14]. Along with the effects that these growth factors and cytokines may exert on other tissue cell types, such as the endothelial cells of the vasculature, they play important roles in bone formation and resorption, including: insulin-like growth factors, transforming growth factors, and bone morphogenic proteins as growth factors promoting osteogenesis; epidermal growth factor, granulocyte-macrophage colonystimulating factor, macrophage-colony stimulating factor, and tumour necrosis factor as growth factors stimulating osteolytic resorption; platelet-derived growth factor and fibroblastic growth factor which have contributory effects to both bone formation and resorption; prostaglandins and leukotrienes as osteolysis-stimulating cytokines; and interleukins that may directly or indirectly stimulate either bone formation or resorption depending on the interleukin family in question [35]. Strong links exist between the skeletal and vascular systems and, along with a strong vascular and nerve presence in the periosteum, numerous neurovascular bundles enter the bone through nutrient foramina, descend and ascend the canals of Haversian systems, and enter medullary cavity through Volkmann's Canals [36]. The two systems are interdependent in that the bone relies on the vasculature for the delivery of oxygen and nutrients and that, modulated by osteoblasts, haemato-

**26**

Foot lameness is a physical impairment of a limb that has a negative effect on the freedom of movement of the animal [58, 59]. It is accompanied by clinical signs linked to a disturbance of locomotion that is related to hoof pathologies that can be caused by infection, environmental and/or genetic causes [60, 61]. Lameness can also manifest itself in pain and lesions that, in turn, lead to an abnormal gait [62, 63] with undesirable consequences on performance [64] and welfare [65]. This disruption in gait originates from involuntary and voluntary exertions to diminish the level of discomfort and/or pain that are the result of damage or injury of ligaments, muscles, nerves or integument [59, 60], or could be due to asymmetric and/ or uneven feet promoting the development of foot lameness [66].

Virtually all ungulate animals can be affected by foot lameness [67–70]. However, our knowledge concerning the aetiology of the condition is often related to the economic implications of the animal in our society [58, 62]. Foot lameness is classified into acute and chronic types depending on the severity of lesions and the

#### **Figure 6.**

*The anatomical displacement (indicated by \*) of the distal phalanx. (A, B) Longitudinal section of two laminitic feet shows lamellae wedge inside the hoof capsule indicates (\*) abnormal tissue, which changed the shape of hoof capsule.*

time requirement for healing, if healing is possible [71]. In dairy cows it represents the most important financial and welfare problem faced by the industry [60], as it is responsible for a drop in reproductive efficacy, a decrease in milk production, and increased culling rates [5, 69]. Similarly, in horses, foot lameness is a significant and predominant medical disorder which accounts for about to \$1 billion in losses annually for the equine industry in the United States of America [72, 73]. In the UK, the maintenance of each horse is estimated to cost about £2660 annually and much of this in the treatment of foot lameness [74]. Foot lameness in the horse is the most prevalent and frequent medical issue, affecting about 11% of the general equine population in the UK in 2011 [75]. This rose significantly in 2012 to 18.6% [76] and was thought to be due to factors such as differing foot balance, shoeing and trimming techniques. Some subpopulations however, seem to be more affected than others as, for example, it is estimated that nearly 33% of dressage horses in the UK suffer from foot lameness [69]. The clinical diagnosis of foot lameness in the equine population is subdivided into scores ranging from 0 to 5 depending on the degree of the condition, with 5 being the worst outcome [77].

Lame horses adapt their gait to compensate for the pain originating from damaged tissues or foot lesions [78–80]. Accordingly, foot lameness is considered to be one of the most common signs of kinetic disorder affecting the musculoskeletal system [30]. As forelimb foot lameness is more common than hind limb foot lameness [81], it has been suggested that conformations of the distal limbs may have a substantial impact in the development of front and rear limb foot lameness [66]. The relatively high prevalence of forelimb foot lameness [81] which reaches to more than 75% of equine foot lameness being found in a forelimb particularly in breeds such as Thoroughbred horses and 40% in Standardbred racehorses [82]. This may be explained by that fact that the centre of gravity of the horse is closer to the front limbs than the rear limbs, as the loading ratio is spread approximately 60% forelimbs: 40% hind limbs [66]. Other research [80] has shown that horses with severe foot lameness in the front limb display an untrue foot lameness in the contralateral rear limb, whereas horses with a real rear limb foot lameness exhibit an incorrect foot lameness in the ipsilateral front limb.

Although the aetiology of equine foot lameness is still an active research area, recent efforts have also tried to determine whether the hoof shape is a disposing factor for foot lameness-causing lesions. The investigation of variations between foot lameness and non-foot lameness affected horses [51], demonstrated that the angle between the capsular wall and the ground is larger in the lame horse with an enlarged heel, curved or misshapen coronary band, that diverging growth lines can occur, and that the tubular horns differ from non-lame horses. It was suggested that hereditary influences and trimming are factors contributing to the asymmetrical shape of the hoof [83, 84].

In chronic foot lameness, the hoof capsule of the lame foot can be more distorted than in the non-lame one [85], as a result of altered loading forces applied to the hoof, hence affecting the shape of the hoof and the internal structures of the foot [86, 87]. These variations in the shape of the capsule are triggered by biological sources causing autolysis of the collagen fibres connecting the epithelium to the bone [68]. The role of these fibres is to support and suspend the weight of the horse via the distal phalanx, as well as to maintain the shape of the capsule constant [88, 89]. Another cause that could lead to hoof distortion is the ability of the foot to produce keratinous material proximally [90]. A number of chronic foot lameness states can be related to sheared heels causing palmar foot pain and hoof deviation [34]. Sheared heels are considered as one of the main causes of foot lameness in the equine genus, which results from an abnormal stride and persistent uneven weight bearing [91]. This leads to higher soft tissue strains that predispose the hoof capsule to deformation [92].

**29**

**6. Conclusions**

**Acknowledgements**

0000-0001-8518-4205.

*The Anatomy, Histology and Physiology of the Healthy and Lame Equine Hoof*

The hoof conformation seems to be a two-way process whereby the hoof shape is a key factor in foot lameness [54, 93] and foot deformation can arise as a consequence of foot lameness [85]. However, there has been little evidence showing that malformation is one of the predisposing factors for foot soreness and foot lameness. Dyson and colleagues [39] highlighted that, despite the differences in the shape of the distal phalanx between horses, lameness is mainly associated with changes in the direction of the dorsal hoof wall. For example, constant shoeing has an impact on the way in which the hoof grows and can, over time; result in a different foot conformation/capsular shape, which can have an effect on foot lameness [15, 40]. Recent bovine work using micro CT has shown that lame cows can present with additional bone growth on the distal phalanx [94]. It is important to remember that comparative findings in other animals could provide crucial evidence which may be applicable to horses and is therefore a further consideration for work in this area. The methodologies which are used are also being developed over time and giving new insights into anatomy and physiology. In a recent study looking at foals with osteomyelitis it was shown how important newer techniques such as CT could be used to compliment traditional radiography whilst also providing novel information about disorders [95], the emerging evidence indicating that CT may be superior at detecting osseous changes in general in comparison to traditional techniques. The number of studies comparing MRI methods to more traditional methods is also highlighting the knowledge that can be gained in not only osseous tissue but also in soft tissue. For example in recent studies in equine limbs lesions where MRI was considered against retrospective patient data/ultrasonography radiography [96, 97]. In addition anatomical knowledge and imaging are becoming increasingly important for new discoveries and techniques in relation to stem cell and gene therapy as highlighted by recent studies using gene therapy to treat equine lameness [78, 98].

There is no doubt that understanding the anatomy, histology and physiology of the equine foot and limb is essential in treating a wide range of disorders. Advances in technology such as magnetic resonance imaging, computed tomography and other imaging techniques also play a role in assisting both anatomical knowledge and understanding equine conditions [99]. Coupled with more traditional techniques recent research has used these techniques to show bone conformation and growth, vascularisation and a number of other factors which could help inform us about anatomy and limb disorders. Although much is known about equine anatomy and histology, more is being discovered in both the normal and pathologically affected horse. In addition, new information from cellular and molecular studies is advancing not only the anatomical and histological sides but also the physiology

The work was funded by PetPlan, Waltham, The Ministry of Higher Education

and Scientific Research of Iraq, Western Scholarship and The University of Nottingham School of veterinary Medicine and Science. We also thank Mr. Craig Sturrock CIPB, Hounsfield Building, University of Nottingham with whom the computed tomography imaging was carried out. Catrin Rutland Orcid: 0000- 0002-2009-4898. Cyril Rauch Orcid: 0000-0001-8584-420X.F. Emily Paul Orcid:

and function of the equine limbs and the disorders they are prone to.

*DOI: http://dx.doi.org/10.5772/intechopen.84514*

#### *The Anatomy, Histology and Physiology of the Healthy and Lame Equine Hoof DOI: http://dx.doi.org/10.5772/intechopen.84514*

The hoof conformation seems to be a two-way process whereby the hoof shape is a key factor in foot lameness [54, 93] and foot deformation can arise as a consequence of foot lameness [85]. However, there has been little evidence showing that malformation is one of the predisposing factors for foot soreness and foot lameness. Dyson and colleagues [39] highlighted that, despite the differences in the shape of the distal phalanx between horses, lameness is mainly associated with changes in the direction of the dorsal hoof wall. For example, constant shoeing has an impact on the way in which the hoof grows and can, over time; result in a different foot conformation/capsular shape, which can have an effect on foot lameness [15, 40]. Recent bovine work using micro CT has shown that lame cows can present with additional bone growth on the distal phalanx [94]. It is important to remember that comparative findings in other animals could provide crucial evidence which may be applicable to horses and is therefore a further consideration for work in this area.

The methodologies which are used are also being developed over time and giving new insights into anatomy and physiology. In a recent study looking at foals with osteomyelitis it was shown how important newer techniques such as CT could be used to compliment traditional radiography whilst also providing novel information about disorders [95], the emerging evidence indicating that CT may be superior at detecting osseous changes in general in comparison to traditional techniques. The number of studies comparing MRI methods to more traditional methods is also highlighting the knowledge that can be gained in not only osseous tissue but also in soft tissue. For example in recent studies in equine limbs lesions where MRI was considered against retrospective patient data/ultrasonography radiography [96, 97]. In addition anatomical knowledge and imaging are becoming increasingly important for new discoveries and techniques in relation to stem cell and gene therapy as highlighted by recent studies using gene therapy to treat equine lameness [78, 98].
