May
25
Written by:
Surgi-Care Center for Horses
5/25/2011 3:46 PM
“Navicular
disease/ Navicular syndrome” are the terms used to define a number of different
conditions that give rise to a chronic forelimb lameness characterized by heel
pain and associated to the navicular bone and surrounding structures. Many
theories have been proposed for the cause of this disease/syndrome. Currently
the most accepted theory involves both biomechanical forces and conformation.
During weight bearing the bottom half of the navicular bone is subjected to
large compressive forces. In horses with poor conformation these forces can be
supraphysiological. The typical conformation of a horse with “navicular
syndrome” is small feet, upright pastern, broken hoof-pastern axis or a long
toe/low heel. Horses
affected with navicular disease/navicular syndrome have an average age of 9
years and the most common breeds affected are Quarter Horses, Thoroughbreds and
Standardbreds. Common presenting complaints from the horse owners are a short
–stride, stumbling and toes wearing off easily (landing on toes).
A
diagnosis of navicular disease will be established following a thorough
lameness evaluation from your veterinarian. Some of the diagnostic tests that
may be performed during the exam are flexion tests, hoof testers, nerve blocks,
radiographs, ultrasound, nuclear scintigraphy, and MRI. A reliable diagnostic
test is the palmar digital nerve block. Blocking (injecting a local anesthetic)
the palmar digital nerves desensitizes the heel area of the foot, therefore if
there is heel pain (which is the case with navicular disease) this block
partially or totally eliminates the lameness. It is important to consider that
heel pain is not always caused by navicular disease, there are other structures
in the heel that can be causing the lameness. If your horse does go sound
following the palmar digital nerve block, your veterinarian will utilize
further diagnostics to determine if the cause of pain is truly from navicular
disease/syndrome, or rather there are other problems going on in the heel region
of the foot.
Radiographs
can support the diagnosis of navicular disease. If no changes are seen in
radiographs, navicualr disease should not be ruled out since some lame horses
show no radiographic findings, while others showing radiographic changes have no
pain. Lesions commonly seen on radiographs consistent with navicular
disease/syndrome, include changes in the navicular bone such as a lost of the
distinction between the junction of the cortex (outer) and medullary (inside)
cavity of the bone, cyst formation, fractures and thining and roughening of the
flexor cortex. MRI and CTscans are other diagnostic modalities that can be more
sensitive than radiographs. Nuclear scintigraphy (“bone scan”) is also a
valuable diagnostic tool especially when the radiographic findings are minimal
and do not support the clinical findings.
As
is the case with many degenerative conditions, there is no cure for navicular
disease, but it can be managed. Treatments are instituted to decrease trauma to
the bone and the navicular bursa, to improve navicular bone circulation and to
arrest the degenerative process. The first line of treatment usually involves
corrective shoeing, pain management (phenylbutazone) and rest or modified
exercise. Corrective shoeing is a very important aspect of the treatment. The
goal of corrective shoeing should be to restore and maintain foot balance,
correct any hoof conformation abnormalities, to decrease biomechanical forces
on the navicular bone and protect the injured region. The type of shoes usually
varies between horses, it should be tailored to the particular horse and
determined by your veterinarian and farrier. More aggressive medical treatment
include, but are not limited to joint injections, navicular bursa injections,
Isoxsuprine and Tildren. Your veterinarian will decide which medical treatment
is most appropriate for your horse.
If
no improvement is seen from prolonged medical therapy, a palmar digital
neurectomy (cutting the nerve) can be considered. Neurectomy is usually
performed as a salvage procedure when all else fails. The surgery will
alleviate pain and restore function but the disease will still be present and
progressing. It is important to consider the possible complications from this
surgery, which include: incomplete desensitization of the heel, failure to
recognize (can not feel) a penetrating wound to the heel region, decreased
vascular supply, deep digital flexor tendon rupture and regeneration of the
nerve. Due to the loss of sensation that will result from this surgery it is
important to check the horse’s feet daily for any penetrating injury. It is
important to discuss all possible complications with your veterinarian prior to
choosing this option.
Prognosis
for navicular syndrome is guarded in the majority of the cases because of its
degeneration and chronicity. Treatment will prolong the athletic use of the
horse, but the time greatly varies between horses. Each case is different and
each horse responds to treatment very differently. Your veterinarian and
farrier will work closely together to determine which shoeing regime and which
treatment protocol will most benefit your horse. It is also important to
remember that no one protocol works on all horses and often times the protocol
will change or be updated as the condition progresses.
Contact
Surgi-Care Center for Horses at 813-643-7177 or
email lkuebelbeck@surgi-carecenter.com with
any questions regarding this topic.