Page 131 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

106 CHAPTER 1

VetBooks.ir 1.187 structural lesions of the navicular bone in both acute
CT and MRI are more sensitive in detecting

and chronic disease, including osseous fragments
associated with a defect in the distal margin of the
navicular bone. MRI is currently the preferred
technique for evaluation of the navicular bone in
horses with palmar foot pain. The most common
MRI abnormality seen in horses with both acute and
chronic navicular disease is increased osseous fluid
signal in the spongiosa of the navicular bone on fat-
suppressed (STIR) images. Clinical experience with
MRI in these cases has lead to the documentation of
a whole range of pathological changes in the struc-
ture of the navicular bone and fibrocartilage and
provides support for the concept of progression of
lesions through various stages of damage, as outlined
Fig. 1.187 Close-up lateromedial radiograph in the introduction.
demonstrating a large entheseophyte in the collateral
sesamoidean ligament of the distal sesamoid (arrow). Management
The treatment of navicular disease is more about
managing the horse rather than curing the disease.
oblique; a lateromedial; and a palmaroproximal/ Developing a specific treatment protocol depends on
palmarodistal oblique (flexor) view. The most reliable the ability to determine the exact cause of pain in
findings for diagnosing navicular disease are defects a horse with palmar foot lameness. It is important
in the flexor cortex, medullary trabecular disruption, to determine whether or not the DDFT is injured
medullary pseudocyst formation, medullary sclerosis, (this can only be determined by MRI) as such cases
poor flexor corticomedullary demarcation, proximal require a very long period of rest as a central part of
or distal extension of the flexor border of the bone, their treatment. A variety of treatment options are
distal border fragments, remodelling of the proxi- available to manage navicular disease including: rest
mal border, including entheseophyte formation, and followed by controlled exercise; corrective trimming
the presence of a bi-partite navicular bone. The size, and shoeing; systemic NSAIDs; vasoactive drugs to
shape and number of the synovial invaginations of the improve blood flow; bisphosphonates; anti-inflam-
distal border are more ambiguous features. As there matory intrasynovial medications; and surgical treat-
is a wide variation in the appearance of these synovial ments such as collateral sesamoidean desmotomy
invaginations in horses without lameness, it is impos- and palmar digital neurectomy. In general terms,
sible to base a diagnosis of navicular disease, or to horses with no or few radiological abnormalities
predict the possibility of future navicular disease, on are managed medically using supportive trimming
the appearance of the distal border of the bone. The and shoeing along with isoxsuprine, tiludronate and
absence of radiographic abnormalities does not rule NSAIDs, with the goal of returning them to regular
out the presence of navicular disease. exercise as soon as possible. If the response to medi-
Nuclear scintigraphy is more sensitive than radi- cal management is unsatisfactory, intra-articular or
ography for diagnosing increased metabolic turn- intrabursal corticosteroids can be used. Horses that
over within the navicular bone, but an increase in become refractory to corticosteroid injections, or
radionuclide uptake in the navicular bone is not horses with advanced radiological changes, usually
necessarily the source of pain causing lameness, as require surgical treatment. Rest is not commonly
increased metabolic bone turnover can be a nor- indicated as lameness generally recurs immediately
mal adaptive response to an increase in workload following return to exercise, except in horses with
in sound horses. primary inflammation or contusion of the medulla