Bone Spavin
Alison Green Hanson
Rebecca Emanuel McCain
About the hock
The hock (tarsus) is a complex of
joints of the lower rear limb of the horse.
It is composed of six bones (tarsal bones) that comprise four different
joints. The uppermost or most proximal
joint (tarsocrural) has the widest range of motion. The other three joints are less mobile (low motion joints) but do
experience torsional forces that affect the overall health of the hock. Bone spavin usually affects the two most distal
lower joints of the hock [distal intertarsal (DIT) and tarsometatarsal (TMT)
joints].
What is bone spavin?
Bone spavin
is a common, often painful condition of the two most distal joints of the hock
(DIT and TMT); it is also called true spavin or jack spavin and is a
manifestation of osteoarthritis or degenerative joint disease. The lameness associated with bone spavin
usually has a slow onset with progressively worsening clinical signs.
What causes bone
spavin?
Bone spavin
usually occurs in mature or older horses that are asked to work excessively off
the hind limbs. Repeated compression
and rotation of the bones (as with high speed stops and turns) and excessive
tension on the ligaments and tendons is a prominent component of the whole
disease process. Multiple repetitive
traumatic insults (“use trauma”) to the hock as associated with day to day
training, activities, and competition of these horses is a common factor in the
pathogenesis of osteoarthritis.
Although some horses do not have
observable changes that can be detected or measured, they still suffer from
pain in the hock. When this is the
case, the term blind or occult spavin is instituted. These horses display the clinical signs of bone spavin (such as
pain and/or a reluctance to perform or a reluctance to perform at the previous
level), but not all of the documentable changes are necessarily seen.
Conformation
of the horse is also a factor in the development of bone spavin. Horses with sickle hocks (increased angle of
flexion) or cow hocks (hocks close together and almost touching with the toe
pointing outward) have increased stress on the bony structures of the
joint. Bone spavin can also occur in
conjunction with fractures, infectious joint disease, metabolic bone disease,
and developmental bone diseases of young horses.
How is bone spavin
diagnosed?
Bone spavin can be diagnosed by a
veterinarian by assessing the history of the horse (age, breed and use of
horse), performing a physical exam (joint effusion or swelling, heat, pain on
palpation of the joint), performing a lameness exam (hock flexion, trotting and
circling the horse on a hard surface, intraarticular anesthesia (joint blocks),
and radiographs. Radiography of the
hock may reveal periarticular osteophytes (bony proliferation in proximity with
joint spaces), bone lysis (decreased density of bone), and/or bone remodeling
(increased density of tarsal bones).
Nuclear scintigraphy (bone scan) can also be performed which may reveal
"hot" spots indicative of joint/bone injury. Not all of these procedures are necessary to
diagnose bone spavin. Consideration is
given to the owner’s wishes to either invest in the diagnosis or to invest in
treatment. Although some horses do not
have observable changes that can be detected or measured, they still suffer
from pain in the hock; when this is the case, the term blind or occult spavin
is instituted. These horses display the
clinical signs of bone spavin (such as pain and/or a reluctance to perform or a
reluctance to perform at the previous level), but not all of the documentable
changes are necessarily seen.
Treatment
Treatment of bone spavin can be divided into
three main types: conservative, medical, and surgical. Conservative and
medical treatments focus on reduction of inflammation with or without
protection of the joint cartilage, while surgical treatment involves
arthrodesis (joint fusion), or tendon cutting. The goal of any treatment for
bone spavin is to make the horse pain free. The choice of treatment is
dependent on a variety of factors including the degree of lameness, other
causes of lameness coincidentally present such as back problems, the
progression to ankylosis (natural joint fusion), the type of work the horse is
used for, time and financial constraints, and response to other
treatments.
Conservative treatment makes sense when there are financial constraints,
only mild lameness, radiographic evidence of self-ankylosis, or simply if the
wait-and-see approach is desired. Corrective trimming and shoeing,
controlled exercise, and oral phenylbutazone comprise conservative
therapy. The hoof must be trimmed so that it is balanced, and it should
be trimmed regularly. A flat steel or aluminum shoe is used. To ease breakover, the toe is squared off
and the heel can be elevated with pads or wedged shoes. In general the
horse should be encouraged to perform as much moderate exercise as possible
with the emphasis placed on straight line walking and trotting four to five
times per week. Exercise facilitates
cartilage degeneration once it has begun, and this will lead to desirable
ankylosis of the distal hock joints.
However, in juvenile cases of bone spavin, cartilage preservation rather
than ankylosis is the priority, and exercise is discouraged. Because the distal hocks joint have a low
range of motion, fusion will not significantly affect gait or athletic ability
but will relieve pain. Oral phenylbutazone can be given for an extended period
of time (four to six weeks) if used at a low dose or given only when the horse
will be ridden.
Medical treatment may be either systemic (intravenous or
intramuscular) or intraarticular (injected into the joint). Medical treatment is often recommended in
the early stages of bone spavin. Polysulfated glycosaminoglycans such as
Adequan ® can be given intramuscularly.
These drugs are chondroprotective (protect cartilage) and appear to have
anti-inflammatory activity. Intravenous
sodium hyaluronate is also chondroprotective and may be more beneficial than polysulfated
glycosaminoglycans in an acute flare up of bone spavin. If the results of
systemic treatment are unsatisfactory, intraarticular long-acting
corticosteroids are indicated. It is important to continue systemic
therapy, because it maximizes the effect and reduces the frequency of
intraarticular therapy. The addition of intraarticular sodium hyaluronate
may increase the corticosteroid’s duration of effect. Reduced but
continued exercise should follow intraarticular therapy. Corticosteroids
may actually slowly encourage cartilage erosion, but they also impair healing;
the net effect is slower ankylosis.
Therefore, if rapid ankylosis is the top priority and soundness can be
sacrificed until the joint fusion occurs, both systemic chondroprotectives and
intraarticular therapy may be avoided. However, chondroprotective drugs
as well as nutraceuticals such as chondroitin sulfate and glucosamine may be
beneficial in prevention of bone spavin in a mature, athletic horse.
Several
surgical therapies for bone spavin
are available. There are advantages to performing surgery early in the
course of bone spavin although it is usually not recommended until the horse’s
pain is unresponsive to other therapies. For example, surgery can reduce
the time to achieve ankylosis in the lower hock joints. However, if
advanced radiographic evidence of ankylosis exists, surgery is not
recommended.
One
surgical technique that does not require general anesthesia is the cunean
tenectomy. The cunean tendon (a branch of the tibialis cranialis tendon) is cut, and pressure applied to
the inside of the lower hock joints is relieved. This procedure does not
fuse the hock joints. Joint drilling and plating can be used in
conjunction with cunean tenectomy or separately. Three types of joint
arthrodesis are available. However,
these require general anesthesia. Bone
drilling destroys the cartilage in the joint and initiates new growth between
the upper and lower bones of the joint which arthrodeses the joint.
Alternatively, chemical arthrodesis can be performed with sodium
monoiodoacetate (MIA), which blocks an enzyme pathway, resulting in cartilage
death and joint collapse. Laser
arthrodesis can also be performed to destroy the cartilage; this is the least
invasive procedure for fusing the joint.
A
new therapy for bone spavin has recently been investigated: Extracorporeal
shock wave therapy. High energy shock waves similar to the ones used for
breaking up kidney stones are applied to the joint and surrounding structures. The technique is non-invasive but does
require general anesthesia for the large focused systems to ensure exact
positioning. The exact mechanism by which shock waves work on bone is
unknown. A potential explanation is that the therapy increases the activity
of osteoblasts (bone making cells) which strengthens the bone under the
cartilage. This activity may help maintain joint shape and shock absorption
thus protecting the cartilage, or it may enhance ankylosis. The therapy is safe and appears effective in
the short-term, but long-term effects are unknown.
Prognosis
The prognosis for bone spavin is always guarded. A
prognosis cannot be given until the gamut of therapies has been attempted,
including surgery, especially when ankylosis is in progress. Of the
arthrodesis options, chemical arthrodesis has been reported as more successful
than surgical arthrodesis (drilling technique) but with many more potential
side effects. Laser arthrodesis and shockwave therapy hold promise, but
long-term results are not yet known.
Regardless of the means by which it is achieved, fusion of the lower
hock joints usually results in soundness.
There is clearly no single universally accepted technique to achieve
permanent relief of pain in horses that have developed bone spavin. The
variety of treatments available reveals that each technique has its
limitations, and the unique circumstances of each case must determine the
choice of treatment regime. Every horse is different, but with an
individualized treatment schedule, a horse with bone spavin can often be
maintained as a useful athlete for an extended period of
time.
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