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Common diseases of the foot
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Summary
In the horse, the foot is the commonest site for pain resulting in lameness. In all lameness examinations it is prudent to focus your initial examination on the foot, and the historical quote ‘No Foot, No horse’ is as true now, as it was several centuries ago when this term first arose. The foot, by virtue of its important mechanical role in shock absorption and locomotion, can be afflicted by a range of degenerative and traumatic conditions. Further, diagnosis of foot pathology can be challenging due to the constraint the rigid hoof wall gives to imaging and palpation.
The use of diagnostic local anaesthesia is a key diagnostic tool available to the equine veterinarian, but the accuracy of specific nerve blocks in the foot has become recognised as a major limitation for these techniques in recent years. Imaging techniques, such as radiology and ultrasongraphy have some major limitations in foot orthopaedic diagnosis. In recent years, magnetic resonance imaging has allowed much more accurate diagnosis of many aspects of foot pathology; however this technique is expensive and not always widely available.
Foot diseases in the horse have numerous therapeutic approaches and prognostic outcomes. Often treatment approaches will include a strong interaction between the veterinary surgeon and a farrier. The importance of the foot shape and conformation, and the specific shoeing technique can have major implications for the onset and progression of chronic degenerative foot disease in the horse, and therapeutic/surgical farriery has a significant role in the treatment of such common cases.
Keywords: foot, phalanx, navicular
Abstract
The foot is the commonest site of pathology in the lame horse, and in most cases of lameness it is sensible to initially expect the site of pain will be in the foot prior to concentrating on the more proximal limb. The foot is often a site for acute traumatic pathology. However chronic lameness as a result of degenerative conditions of the foot is extremely common. A significant risk factor for onset of a number of degenerative foot diseases is poor hoof conformation. Frequently such horses will have some degree of poor dorsopalmar foot balance combined with low or collapsing heels. Further, some degree of mediolateral hoof imbalance is not uncommon. Often, where shod, such horses will have overlong toes and the shoes will not extend sufficiently palmar to allow necessary heel support. Such hoof conformational traits will allow accumulation of repetitive mechanical trauma which when accumulated over time resulting in a variety of degenerative disorders associated with the joints, tendons, ligaments and navicular bone.
Clinical assessment
Foot assessment should include assessment of the hoof conformation with the horse weight bearing, and with the horse both at walk and trot. Specific attention should be placed to observing how the foot strikes the ground (ie foot or heel first), as well as how the horse turns short at the end of any walk or trot-up. The horse should be observed at both the walk and trot to identify lameness. In cases of mild lameness, gait assessment whilst lunged in a circle on both a hard and soft surface is an extremely useful technique to identify subtle gait impairment, as well as any bilateral nature to the lameness (which is extremely common in degenerative conditions). Response to both passive flexion and flexion test of the distal joints should also be ascertained. It is useful to identify when the horse was last shod, the type of shoeing, and whether there is any abnormal wear to the foot or shoes.
Specific clinical examination should include careful palpation of the foot to identify any sites of abnormal heat and inflammation. Digital pulses should be assessed to assist with identification of foot inflammation. Response to hoof testers should be used to identify any sites of solar pain or sensitivity, as well as determining response to percussion of the foot with a light hammer. Careful examination of the coronary band and the heels should take place to identify any site of exudation or draining tracts. In cases of acute onset lameness, or when lameness has occurred following recent shoeing, it is always sensible to remove the shoe and carefully pare the hoof with a hoof knife and identify any potential sites of solar infection or penetration.
Further diagnostic tests
Diagnostic local anaesthesia has long been an important diagnostic test to determine whether pain is associated with the foot, and potentially localising where the site of pain is. Such approaches can include using perineural local anaesthesia through either palmar digital or abaxial sesamoid nerve blocks. In some cases, intrasynovial anaesthesia through either distal interphalangeal joint or navicular bursal joint block can be useful. In recent years the exact specificity of such techniques has come under some scrutiny, and there is probably less accuracy in such techniques than previously thought; however, they still are an important technique. Diagnostic imaging is of huge importance in defining foot pathology. Radiography can be very useful in some foot conditions (including fracture, osteoarthritis and laminitis) but its limitations are now well recognised since many structures that are commonly injured in foot disease are soft tissues which are hard to discriminate radiologically. Ultrasonography is rarely useful, as imaging is highly constrained by the difficulties of imaging through the hoof capsule.
In recent years the use of cross sectional imaging techniques has shown a huge potential in assisting diagnosis of complex foot diseases. Techniques such as computed tomography and magnetic resonance imaging are both extremely useful in defining foot disease. However, such technologies are expensive and may not be readily available to many areas of veterinary practice. In particularly MRI is hugely useful in foot diagnosis through its ability to define both osseous and soft tissue pathological changes.
Conditions of the foot
There are a vast number of conditions which affect the foot and I will identify and discuss only a selection of the more common diseases. In particular I will mention acute injuries which affect the foot including subsolar infections and the more serious solar penetrations. I will identify common fractures which affect the foot region, as well as traumatic injuries of the hoof wall. In chronic conditions of the foot I will identify distal interphalangeal joint osteoarthritis, navicular syndrome, DDFT injury, distal interphalangeal joint collateral ligament desmitis and palmar foot pain. Key clinical and diagnostic features of these conditions will be identified and brief mention of treatment and prognosis will be given.
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