Navicular syndrome

Navicular disease is really a group of related conditions affecting the navicular bone and
associated structures in the foot. There are several possible causes of pain in and around the
navicular bone.
Anatomy of the navicular region
The navicular bone is a small flattened bone, which lies across the back of the coffin joint. It
attaches to the pedal (coffin) bone via a short strong ligament (the impar ligament) and to the
pastern joint by suspensory ligaments. The deep digital flexor tendon runs over the lower surface
of the navicular bone, which acts somewhat like a pulley and between these lies a small pocket of
fluid, the navicular bursa, which acts like a cushion between the tendon and its pulley.
What causes navicular disease?
At present, the exact primary cause of Navicular Syndrome is not known. Damage to the
navicular bone may occur due to interference with blood supply or trauma to the bone. Damage
can occur to the deep flexor tendon, navicular bursa, or navicular ligaments all resulting in pain
and lameness. Conformation and unbalanced trimming contribute greatly to the disease. It is
somewhat inherited, either directly or in the inherited conformation of the feet that makes a horse
more prone to navicular disease.

What are the symptoms?
Navicular disease affects the front feet of horses causing a low grade bilateral lameness, which
usually progresses slowly. The lameness might only occur from time to time or when the horse is
exercised on hard ground or in a small circle. In some cases, one foot is affected more than the
other, causing an obvious lameness. Affected horses may stand with the more painful foot in front
placed of the other (pointing).

How is navicular disease diagnosed?
Diagnosis is based on a combination of history, symptoms, nerve blocks and radiography. A
history of intermittent low grade or recurrent lameness is
suggestive of navicular disease. Affected horses often
appear to place the toe down first, as if trying not to put
weight on their heels (in contrast to laminitis), and the
lameness is worse on the inside leg on a circle. Injection
of local anaesthetic (nerve block) around the nerves
sensitizing the back half of the foot and/or into the
navicular bursa will improve or alleviate the lameness
associated with navicular disease. Some cases also
improve when the coffin joint is blocked. Radiographs
may reveal damage to the navicular bone but bone
Radiograph of navicular bone showing
changes can be difficult to interpret, as there are differing chronic change at lower boarder
opinions on what is normal. Navicular syndrome can
exist without demonstrable radiographic abnormality and magnetic resonance imagining (MRI)
may reveal injury to the impar or other ligaments or soft tissues.

What treatments are available?
Navicular disease can be treated and managed, but rarely cured. Corrective trimming and
shoeing is imperative to ensure level foot fall and foot balance. Often a rolled toe egg bar shoe is used to encourage early break over at the toe and good heel support. Medication such as phenylbutazone will elevate pain in many cases and enable work to be resumed. Long term treatment with substances such as isoxsuprine and aspirin may improve blood supply to the navicular bone and improve the condition of the bone. Long term desensitization of the back of the foot can be achieved by performing a neurectomy to cut the heel nerves. This treatment should only be considered as a last resort and then only in full recognition of the implications. Post operative complications are common and include rupture of the deep flexor tendon, painful inflammation of the cut nerve endings (neuromas) and damage to the foot which goes unnoticed by Post mortem navicular
horse and owner. The nerves often grow back and the lameness returns bones showing chronic
within 1-2 years of surgery. Treatment options should be discussed in Can navicular disease be prevented?
Horses with all foot shapes can develop navicular disease. Nevertheless, maintaining good foot
balance and heel support can help to prevent many foot lamenesses. Prepurchase examinations
can help identify affected horses before you buy them.
Daniel P. Keenan, DVM Ron McAlister, DVM Lynsey Makkreel, DVM 165 Third Street ΠBordentown, New Jersey 08505 Π609-291-0535 Πfax 609-291-8899 Π


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