Common Lameness Problems In Endurance Horses - Australian ...

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effects of weight bearing and concussion on compacted surfaces can lead to interference with blood perfusion, bone dissolution with initial subtle lameness on soft surfaces that compact under the soles Affected horses exhibit ‘shuffling’ and ‘proppy’ gait, especially on soft surfaces which is exacerbated after concussive exercise. As the pedal bone becomes more demineralised in more severe cases, in older campaigners, there is an increased risk of fractures of the outer sides of the pedal bones where greatest demineralisation and increase in vascular channelling occurs, as seen on X-ray. Ensuring that a horse’s hooves are trimmed and shod to reduce sole contact, and fitting underpads to horses with thin or flat soles, will help to reduce the risk and the severity of pedal bone concussion and associated lameness. Horses that have had any previous history of laminitis or mild founder, with any degree of downward rotation of the pedal bones and collapse of the soles, are more prone to concussive hoof injury. It is important that they are shod to support and protect the under surface of the sole and frog. Although demineralization cannot generally be reversed, even by providing calcium and bone minerals in excess relative to dietary requirements and resting the horses for extended periods, therapy to increase blood perfusion within the hoof and pedal bone, such as by fitting magnetic bell boots overnight, may help to slow down the progressive demineralisation. Navicular Syndrome and Coffin Joint Arthritis Although “navicular syndrome”, as it is now termed, is largely influenced by genetic predisposition, especially in horses with naturally small, contracted hooves, the concussive effects of long distance exercise can result in vascular changes within the navicular bone and arthritis in the associated coffin join. This progressive deterioration is now collectively referred to as navicular syndrome, rather than navicular disease. The navicular bone acts as a pulley implanted in the relative avascular upper structure of the deep flexor tendon as it passes over the coffin joint to attach on the under surface of the pedal bone. High loading forces in exercising horses of up to 40,000 Newtons (1000 lbs per square inch) are thought to restrict blood supply to the navicular bone. Although early stage navicular deterioration is often responsive to oral vasodilating therapy (termed isoxsuprine responsive), new studies reveal that fluid pressure accumulates within the navicular structure to cause demineralisation and internal collapse of the navicular body. The fluid eventually erupts through the articular surface of the navicular bone into the coffin joint, resulting in progressive arthritic change. Early navicular disease is recognized by a stumbling gait, especially when moving downhill, increased wear on the toes of shoes, and a “scratchy” gait that often warms out on exercise returning to be more obvious for 2-3 days after a ride. Horses often appear to be “tied-up in the shoulders” because of the shortened stride length, and stand resting on the toe of the affected hoof(s) to relieve pressure on the painful navicular bone.
The progressive deterioration and associated pain of diminished blood supply and internal fluid accumulation, results in avoidance of heel contact, with development of higher and contracted heels, and deeper grooves (sulci) around the frog, with a progressive chronic lameness. Diagnosis by nerve blocks, X-rays and coffin joint anaesthesia can help confirm navicular syndrome in chronic cases. The use of rolled toes to hasten break-over and support to the heel area with eggbar shoes, with or without heel wedges, will improve comfort and gait in early cases. Daily supplementation with glucosamine based oral joint preparations (reviewed in a separate section in this publication) can provide relief of early navicular related arthritic changes in the coffin joint, in conjunction with therapeutic shoeing and regular hoof care. Recently, the use of magnetic bell boots with strong magnetic fields above 1500 gauss (Animal Magnetism, Wyong, Aust) have been observed to provide relief in early cases of navicular syndrome, presumably by improving blood perfusion within the navicular bone and hoof structure. Laminitis Laminitis caused by tearing and deterioration of the laminae attachment of the hoof wall to the pedal bone within the hoof capsule, can occur as a result of extreme concussive exercise, often referred historically as “road founder”. Although 80% of laminitic conditions result from starch overload from excess grain (such as corn) or very lush pastures (containing fructan sugars and other soluble non-structural sugars), during spring in grazing horses, the average endurance horse in training, with a controlled diet and “fit” body condition aided by regular exercise, is unlikely to develop a carbohydrate overlaod type “founder” condition. Concussive exercise on hard ground at speed can result in physical tearing of the laminae, with shortened stride and a ‘leaning back on the heels’ stance, often with an increased digital pulse. Prompt first aid with ice packs and antiinflammatories, and rest, as prescribed by a veterinarian, will help resolve milk tearing of the laminae in an otherwise healthy hoof. Ring Bone The bony growth referred to as “ring bone” associated with the pastern and coffin joints is often a result of long term concussion, and is most prevalent in Arabian and other breeds of horses with lightly boned and long sloping pasterns and turned out toe conformation. Initially, peri-articular bone reaction, due to collateral ligament tearing away from the pastern bones and bone surface (periosteal) reaction above or below the joint, as a result of twisting and overflexion of the pastern joint, can cause shortening of the stride and a ‘scratchy’ gait. However, continued concussion, especially when the collateral ligaments are stretched and allow excess bone on bone movement within the pastern joint, can lead to cartilage damage and subchondral bone pain within the pastern joint. This results in chronic intra-articular ring bone in one or both front limbs. The lameness associated with early peri-articular ring bone can be alleviated by judicious use of anti-inflammatories, including DMSO and Dermcusal (Vetsearch, Australia), but if the bony proliferation encroaches into the pastern joint, then arthritic changes develop which
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Common Lameness Problems In Endurance Horses - Australian ...

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