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MEET BORIS ….. (Navicular Disease)

 

Boris imageBoris is a dutch gelding who presented with a sudden onset right forelimb lameness subsequently diagnosed and under treatment for Navicular Disease.

 

 

 

 

 

 

Navicular Disease

 

Navicular Disease is a complex condition which involves damage to the navicular bone, the coffin joint, tendon and ligaments. It is a problem that can affect all four feet but is really only considered in the front feet. There is a definite hereditary conformation predisposition with Thoroughbreds being over represented and Arabs rarely affected, typically low heel and long toe foot conformation contributes as well as contracted feet.

 

The visual presentation is a horse over 4 years old with an intermittent fore limb lameness which initially responds to a few days box rest and is worse the day after hard work.   It is commonly suspected to be coming from the shoulder by the horses owner because of the obviously shortened stride in the more severely affected limb, usually both limbs are affected one worse so than the other. The disease progresses to a stage where the horse is lame most days and lameness is aggravated by work and turn out. Often the horse lands the affected leg toe first to avoid the pain in the heel, even to the point that the toe becomes very badly bruised and confuses the diagnosis as this itself is painless. Navicular disease affects a number of structures situated close to the navicular bone. The bone itself becomes weakened as it thins in specific areas due to 2 processes. Firstly a reduced blood supply caused by clots in the arterioles supplying the bone and secondly increased bone turnover by specialist cells that remove the bone. The poor confirmation seen in many cases contributes to damage to the deep digital flexor tendon which is put under increased pressure and degenerative joint disease of the distal interphilangeal joint (coffin joint).   There is also a ligament between the navicular bone and the pedal bone which is damaged in navicular disease.  

 

A diagnosis of navicular disease normally requires both a response to nerve blocks (palmer digital or navicular bursal) and significant x-ray changes. This is because it is possible to x-ray a sound horses feet and find moderate to severe changes in the navicular bone. These animals are likely to suffer with lameness at a later date.

 

The classic and common radiographic changes are the large “lollipop” shaped defects in the 60 degree upright view and thinning of the cortex, the dense border of the navicular bone.   The disease is progressive and will not be cured therefore the aim of treatment is to manage and remove the pain. This is addressed in several ways.   In the short term administration of anti inflammatory drugs is used alongside the more long term aids including corrective showing and more specific drugs. Egg bar shoes are the basis of any successful treatment, providing the correct balanced support for the feet ideally controls 100% of the pain.   Another common component of treatment is Isoxuprine (Navilox) which is a drug used to increase the blood flow to the navicular bone based on the theory that the disease is at least partially cause   by a reduced blood flow to the bone. There is also an injectable drug available which is designed to slow the breakdown of bone by the body.   If an affected horse responds to the initial treatment it will be for a variable amount of time and the horse is likely to need short courses of painkillers until it eventually becomes permanently lame. This could vary between a period of weeks or years. At this point if a patient fails to respond to treatment at all there is a salvage procedure whereby the nerves to the foot are transected (a Neurectomy) immediately relieving the pain. However, in my opinion, this operation has serious welfare implications as the horse could develop neuromas (painful swellings of the nerve endings) or suffer traumatic injury to the feet and be unaware of it.

 

 


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