Download Review of Equine Distal Hock Inflammation and Arthritis

IN-DEPTH:
HOCKS
Review of Equine Distal Hock Inflammation and
Arthritis
Brad R. Jackman, DVM, MS, Diplomate ACVS
Author’s address: Pioneer Equine Hospital, 11501 Pioneer Avenue, Oakdale, CA 95361;
e-mail: [email protected]. © 2006 AAEP.
1.
Introduction
The tarsus is a common etiology of hindlimb lameness in the horse. The distal intertarsal and tarsometatarsal joints are considered the wear and tear
joints of the hindlimbs and are a common source of
reduced performance. Conformation, such as a
sickle hock, may increase the stress across the distal
hocks, but occupation and athleticism are the chief
culprits involved with increasing the shear and rotational forces through these joints. Horses with
distal hock pain can often be managed conservatively and maintain their athletic career. Occasionally, more aggressive methods of management
are indicated and necessary.
2.
Anatomy
The hock is composed of 10 bones and 4 joints.
The proximal tibiotarsal or tarsocrural joint is the
high-motion joint of the tarsus, and it is comprised of
the tibia, talus, and calcaneus bones. The three
lower joints are the proximal intertarsal, distal intertarsal, and tarsometatarsal joints in a proximal
to distal direction. The distal intertarsal joint is
bordered by the central tarsal bone proximally and
the third and fused first and second tarsal bones
distally (Fig. 1). The fourth tarsal bone spans the
distal intertarsal joint laterally and articulates with
both the proximal intertarsal and tarsometatarsal
joints. The tarsometatarsal joint lies between the
distal row of tarsal bones and the proximal aspect of
the metatarsal bones (Fig. 2). Each of these joints
has minimal flexion-extension motion, and most of
the stress applied through them is rotational and
shear.
The proximal intertarsal joint communicates with
the tibiotarsal joint, and therefore, disease of the
proximal intertarsal joint can be considered possible
disease of a high-motion weight-bearing joint.1
For the most part, the distal intertarsal and tarsometatarsal joints do not communicate with either
the proximal intertarsal or tibiotarsal joints.
There have been varying reports of communication
of 8.3– 67% between the distal intertarsal and tarsometatarsal joints, but, in general, they are
thought to communicate ⬃30% of the time.1–5 The
communication seems to occur between the third
and the combined first and second tarsal bones
and/or the tarsal canal.1,4
3.
Lameness Diagnosis
The degree of lameness related to pain emanating
from the distal intertarsal and tarsometatarsal
joints can vary from mild and performance hindering to relatively severe. As with all horses pre-
NOTES
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Fig. 1. Medial view of the bones of the equine hock. The asterisk denotes the location for needle placement within the distal
intertarsal joint in palpable depression distal to the central tarsal
bone and at the proximal junction of the combined first and
second tarsal bone and the third tarsal bone.
sented for lameness, the examination should
commence with a thorough and accurate history as
well as a comprehensive visualization and palpation
of the musculoskeletal system. An accurate history
from the owner or trainer is invaluable, especially in
cases of reduced performance. Any time that the
chief complaint is reduced performance, such as a
prolonged time in speed events, reduced stopping
and turning capabilities, rails knocked down or
jump refusals, trouble picking up or holding leads,
or development of other performance or behavioral
changes, inflammation and/or osteoarthritis of the
distal tarsal joints should be a primary rule out.
Physical examination should include palpation of
the back, forelimbs, and hindlimbs. Particular attention should be focused on pain associated with
the forelimb suspensory ligaments as well as the
lumbar and gluteal muscles. Often, horses with
distal hock pain will place more pressure through
the forelimbs, and proximal suspensory pain may be
present. Any joint effusion should be noted, although effusion of the distal tarsal joints is not capable of being palpated. Occasionally, a firm
swelling will be present on the distal medial aspect
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Fig. 2. Lateral view of the bones of the equine hock. The asterisk denotes the location for needle placement within the tarsometatarsal joint between the distal aspect of the fourth tarsal
bone and the proximal aspect of the fourth metatarsal bone.
of one or both hocks and may indicate more advanced osteoarthritis (Fig. 3). Pain related to palpation of the plantar medial hock in the region of the
cunean tendon and bursa and the head of the second
metatarsal bone may be present but is unreliable.
Any conformational flaws such as sickle hock or
hindlimb base narrow should be noted, because
these issues may increase stress applied through the
distal hock joints.
Motion examination should occur at a walk and
trot in a straight line and circle as well as a canter in
a circle. There needs to be no tension on the horse’s
head during the examination to allow for accurate
evaluation of movement. It is also frequently helpful to examine the horse when ridden, although not
necessary in the majority of cases. A characteristic
gait related to lameness from the distal hock joints
has been described as an adduction of the hindlimb
with an abrupt abduction occurring just before the
limb contacting the ground and has been referred to
as a “stabbing” gait.6 Although this is frequently
evident, it is not pathognomonic. Horses can exhibit this gait with lameness originating from other
causes, and distal hock pain may also present with a
different gait. It is also common for the most evi-
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Fig. 3. Large firm swelling present on the distal medial aspect of
the left tarsus. This may indicate more advanced osteoarthritis
of the distal tarsal joints.
dent gait problem to be a caudal shortening of the
stride when circling if the affected limb is the outside limb. Flexion tests of the distal and upper
hindlimbs can help differentiate the likely source of
lameness. Lameness related to the distal tarsal
joints usually causes an exacerbation of the gait
deficit seen on the initial straight trot. Severe responses to upper hindlimb flexion are rare with distal hock pain, and other sources of lameness should
be explored.
A presumptive diagnosis of lameness related to
the distal tarsal joints may be made with a supportive history and clinical examination (i.e., the primary complaint is reduced performance, and the
clinical examination reveals only a mild gait deficit
that is slightly to moderately exacerbated with upper hindlimb flexion). However, if any suspicion
exists of another source of lameness, the examination should continue with the use of perineural and
intrasynovial anesthesia. Intra-articular anesthesia of the distal intertarsal and tarsometatarsal
joints can be performed to help localize the lameness. One has to be cautious in interpreting the
results, because diffusion of mepivacaine occurs between joints as well as surrounding soft tissues.
Although arthrographic studies have shown that the
distal intertarsal and tarsometatarsal joints communicate ⬃30% of the time,1–5 mepivacaine has
been found to diffuse readily (nearly 90%) between
both the distal intertarsal and tarsometatarsal
joints and the tibiotarsal joint.7 Additionally, the
tarsometatarsal joint also has plantar outpouchings
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along the proximal aspect of the proximal metatarsus just axial to the splint bones. Diffusion of local
anesthesia from these pouches may also desensitize
the proximal suspensory ligament, and similarly,
infusion of local anesthetic at the origin of the suspensory ligament may desensitize the tarsal joints.
Attempting to localize the source of lameness may
require several examinations with the performance
of different blocks at different times.
Radiographs of the tarsus should be performed if
the lameness has been localized to the region or if
any inflammation or abnormality of the tarsus is
suspected. Quality radiographs require an adequate number of views, proper positioning, and good
technique. A minimum of four views should be
obtained including a lateral, dorsoplantar, dorsolateralplantarmedial oblique, and dorsomedial-plantarlateral oblique, because abnormalities may only be
present on one view. Occasionally, special views
such as a flexed lateral and plantar-skyline view
may be indicated and helpful. Often, a small, subtle lesion will be present on one view only. Assessment of joint surfaces requires proper positioning
with the limb square under the horse with equal
weight bearing. The increasing availability of digital and computerized radiography has improved the
detail, which allows for more subtle lesions to be
identified. In many cases, inflammation can be
present within the distal tarsal joints without radiographic evidence of disease. If changes are present,
they frequently consist of small osteophytes, jointspace narrowing, bone sclerosis, or small areas of
lysis.8 –10 In more severe cases, there can be extensive bone exostosis, aggressive lysis, and severe narrowing of the joint space or even ankylosis (Fig. 4).
Ultrasonography of the inflamed or arthritic distal tarsus is usually of limited diagnostic value.
The narrow width of the joints limits evaluation of
the joint capsule, articular cartilage, and intertarsal
ligaments. The medial and lateral collateral ligaments have both a long and short component and
can be evaluated. Bony proliferation can usually
be diagnosed with quality radiographs; however, ultrasound examination of the plantar tissues and
proximal suspensory ligament can be invaluable in
determining pathology in closely related regions.
As magnetic resonance imaging and computerized
tomography become more available, the type and
degree of pathology of the distal tarsal joints may be
further defined.
Nuclear scintigraphy is occasionally used to aid
with the diagnosis of distal tarsal inflammation.
It is rarely needed in the typical case, but it can
be very helpful in horses not amenable to intraarticular anesthesia or to rule out other sources of
lameness. Normal horses exhibit a greater radiopharmaceutical uptake in the dorsal and lateral aspects of the joint.11 Compared with horses with
diagnosed distal tarsal pain, there was a significant
increase in radiopharmaceutical uptake in painful
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Fig. 4. Dorsolateral-plantarmedial oblique radiograph of the
tarsus with severe narrowing and lysis of the distal intertarsal
joint.
limbs, especially if osteoarthritis was radiographically apparent.12
At times, it may be difficult to completely determine the precise source of lameness. The physical
exam may be suggestive of distal tarsal inflammation or arthritis but not completely confirmed with
the use of anesthetics or imaging. In those situations, a presumptive diagnosis can be made and
later confirmed if a positive response to intra-articular medication occurs.
4.
Non-Surgical Treatment
As most clinical conditions related to the distal tarsal joints are primarily performance-limiting problems, owners generally prefer maintaining the horse
in their occupation if there is not a risk of future
damage. Treatment is directed at reducing inflammation in the affected region and keeping the horse
in performance training.
Systemic anti-inflammatory medication is accomplished with the use of non-steroidal anti-inflammatories (NSAIDs). Both phenylbutazone and
flunixin meglumine are commonly used and can be
effective; however, because the inflammation and
trauma to the region is related to occupational
strain, NSAIDs are transiently effective and of lim8
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ited use for long-term therapy if the horse continues
to perform. Supplementation with IM polysulfated
glycosaminoglycans, oral glucosamine/chondroitin,
or IV hyaluronan may also be beneficial and is more
commonly used as maintenance therapy. Additionally, the topical application of diclofenac liposomal
cream over the distal tarsus can benefit some horses,
but the response is inconsistent.13
The most effective way to treat distal tarsal inflammation while the patient is performing is with
local injection of the distal joints with corticosteroids. Often, intra-articular hyaluronan is added,
because it has anti-inflammatory properties and to
reestablish the joint environment. The most common corticosteroid used is methylprednisolone
acetate. Other corticosteroids used include triamcinolone acetonide and less frequently, betamethasone. Controversy exists as to whether both the
distal intertarsal and tarsometatarsal joints need to
be injected. A recent study showed that injection of
methylprednisolone into the tarsometatarsal joint
achieved diffusion of methylprednisolone into the
distal intertarsal joint in therapeutic concentrations; however, these concentrations were ⬃50 times
lower than the concentration within the tarsometatarsal joint.14 The author still prefers to inject both
joints individually, because clinically, there have
been horses with a superior clinical result versus
injection of the tarsometatarsal joint alone. In general, the majority of horses can be managed with
periodic injection of the distal joints throughout
their athletic career. Although corticosteroids
have been shown to have negative effects regarding
cartilage metabolism,15,16 their repeated use does
not clinically seem to enhance the progression of
degeneration within the joint. Likely, the ability to
keep the horses in work and the repetitive strain on
the joints is what causes further progression of the
arthritis in a limited number of cases.
Recently, tiludronate has been used in the treatment of distal tarsal inflammation. It has been
used more frequently in Europe and the United
Kingdom, and the author has limited experience
with the medication. Tiludronate is a bisphosphonate compound that theoretically has antiresorptive
properties by inhibiting osteoclastic activity.
There are few controlled studies with this medication, and in a small double-blind clinical study, only
one of eight horses improved with the administration of tiludronate for distal tarsal inflammation or
arthritis.17 Further studies are needed to effectively evaluate this treatment.
Extracorporeal shockwave treatment (ESWT) has
also been used in the treatment of distal tarsitis.
Both focused and radial portable units are available
and have been used. There has been one published
retrospective study where 74 horses with osteoarthritis of the distal tarsal joints were treated with
ESWT.18 These horses were selected as cases, because they had a diminishing or unsatisfactory response to routine intra-articular injections. They
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reported complications include persistent swelling,
septic arthritis, skin sloughing, and increased lameness. This technique has fallen out of favor because of the initial severe pain and significant
possible complications.
5.
Fig. 5. Application of a focused extracorporeal shockwave treatment to the distal tarsus.
were treated with a focused unit under general anesthesia. There were 139 joints treated in the 74
horses, and 80% of the horses had improvement in
their lameness of at least one lameness grade; however, only 18% of the horses became clinically sound.
The author occasionally uses standing focused
shockwave therapy with some benefit in horses that
have become refractory to routine intra-articular
medication (Fig. 5).
Chemical arthrodesis of the distal intertarsal and
tarsometatarsal joints has been performed with the
use of sodium monoiodoacetate (MIA). MIA is a
very irritating chemical that induces an inhibition of
chondrocyte glycolysis and death.19 This technique
can only be performed if the joints can physically be
injected, and care must be taken to ensure that the
correct joints are injected. Contrast arthrography
is necessary to ensure accurate needle placement as
well as confirm if any communication with proximal
joints is present. Generally, 100 mg of MIA diluted
into 2 ml of sterile saline solution is injected into
each affected joint. After injection, pain control is
necessary with the use of analgesics and anti-inflammatories, because severe pain is often present
for 4 –18 h post-injection. Perineural analgesia
with bupivacaine of the peroneal and tibial nerves
will also help alleviate the pain. Several studies
have shown that 75– 85% of horses have been free of
lameness with radiographic evidence of joint fusion
at ⬃6 mo after treatment.17,19 –21 However, because horses were followed for several years after
treatment, the success rate decreased, and a significant number of horses developed arthritis of the
proximal intertarsal and tibiotarsal joints. Other
Surgical Treatment
Many different techniques have been reported for
the treatment of distal tarsal arthritis. These include cunean tenectomy, subchondral forage,
neurectomy, and several different techniques of surgical arthrodesis.22– 40 The reason so many techniques exist is that there has not been one single
technique shown to be vastly superior to the others.
Additionally, there is likely tremendous individual
variation in the clinical patient both in disease process and definition of successful outcome.
Cunean tenectomy has been described for several
decades as a treatment for distal tarsitis. Theories
of its use have been to reduce the pressure over the
medial aspect of the distal tarsus and cunean bursa;
additionally, it might reduce the rotational and
shear stress over these joints during contraction of
the tibialis cranialis muscle. The procedure is generally performed in the standing sedated horse with
local anesthesia. A linear vertical incision is made
over the palpable cunean tendon on the medial aspect of the hock. Curved hemostats or forceps are
used to identify the tendon, and a 1.5- to 2.0-cm
section of cunean tendon is excised. Routine skin
closure is performed. Reports of successful outcome in racehorses has been variable, but an ownersurvey study reported an 83% good or excellent
outcome in 285 horses, although 30% of the horses
required further medical treatment. The author
has generally used a cunean tenectomy in those
cases with radiographic evidence of medial bone proliferation. Periodic intra-articular medications
have usually been necessary post-operatively.
Subchondral forage or fenestration involves the
drilling of tracts across the joints and into the bones
in an effort to reduce subchondral bone pressure.
Bones adjacent to osteoarthritic joints often become
sclerotic with a resulting increase in intraosseous
pressure. Fenestration has been performed
through stab incisions on the medial aspect of the
tarsal region in a distal to proximal direction; it
begins in the proximal third metatarsal bone and
extends proximally and obliquely through the tarsometatarsal joint, third tarsal bone, and distal intertarsal joint and into the medullary cavity of the
central tarsal bone. Radiographic or fluoroscopic
guidance is recommended to avoid penetration of the
proximal intertarsal joint. Conversely, the drilling
can commence in the central tarsal bone and extend
distally to the third metatarsal bone. Additionally,
a more subtle fenestration can occur at the time of
arthrodesis using intra-articular drilling. Studies
to evaluate subchondral fenestration are limited,
but in one study, 66% of horses treated returned to
their intended use. The clinical significance of subAAEP PROCEEDINGS Ⲑ Vol. 52 Ⲑ 2006
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chondral bone pressure in distal-tarsal osteoarthritis is currently unknown.
A technically difficult procedure of transection of a
portion of the tibial nerve and its branches, the deep
peroneal nerve, and the plantar nerves has been
described. The procedure is performed under general anesthesia with the use of a tourniquet. This
study reported a success rate of eliminating lameness in 83% of horses at 2 mo, but only 61%
remained sound for 12–36 mo. Presumably, regrowth of the nerves occurs over time, reducing the
long-term effectiveness. The author has no personal experience with this technique and is reluctant to pursue its use related to the non-selective
desensitization that occurs.
The most common surgical technique used in the
treatment of distal tarsal osteoarthritis is facilitation of fusion of the affected joints. A natural ankylosis of the joints is preferred, and further
intervention is only indicated if the patient cannot
continue in performance work despite medical therapy or if the lameness is severe. Fusion of the joint
results in stabilization and subsequent pain alleviation. A true arthrodesis is the removal of joint
cartilage and mechanical stabilization. Most described tarsal arthrodesis techniques are more to
facilitate ankylosis, because these joints have minimal natural motion and are inherently stable. Before considering a surgical arthrodesis, the lameness
needs to be carefully localized to the distal tarsal
joints. Quality radiographic images are necessary
to determine if any proximal-tarsal osteoarthritis
exists, because this would affect the prognosis.
Intra-articular drilling across the distal intertarsal and tarsometatarsal joints is the most frequently
used procedure for distal tarsal arthrodesis. Initial
techniques described a more aggressive procedure
with 60% of the articular cartilage removed. Significant post-operative pain was associated with this
procedure, and a more conservative approach is currently used and recommended. The approach is on
the medial aspect of the limb either through a linear
incision and cunean tenectomy or with the use of
stab incisions. Needles are placed into the joints,
and their positioning is confirmed with radiographs.
Three diverging drill tracts are made with a 3.2-,
4.0-, or 4.5-mm-diameter drill bit to an approximate
depth of 3 cm in each joint. Radiographic or fluoroscopic guidance during drilling is recommended,
and care must be taken to avoid breaking a drill bit.
As previously mentioned, subchondral fenestration
may also be performed at the same time. Postoperatively, a controlled exercise program is followed with the horses returning to exercise after the
lameness significantly improves (generally 2– 4 mo).
A return to full athletic performance usually takes
10 –12 mo. A recent retrospective study evaluating
this technique reported 59% of horses successfully
returning to their previous level of performance and
a further 11% improved. The client should be notified before performing this procedure that com10
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plete ablation of the joint space is unlikely and that
the goal is to create functional bone bridging to
eliminate joint motion and pain.
Both a neodymium:yttrium aluminum garnet (Nd:
YAG) and 980-nm diode laser have also been used to
facilitate arthrodesis of the distal tarsal joints.
The technique involves placing a laser fiber through
a stainless-steel cannula placed into the dorsomedial aspect of the joints. A second needle is also
placed at a distant location to serve as an egress for
the smoke plume generated by the laser. Approximately 800-1200 J of energy are then delivered
through the laser in an effort to boil the synovial
fluid until it vaporizes. The heat generated causes
chondrocyte death and a collagen shift in the joint
capsule and intertarsal ligaments. Several studies
have shown that horses treated with laser-facilitated arthrodesis are more comfortable after the
procedure than when surgical drilling or MIA is
used. It has been theorized that the superheating
occurring with the laser may cause thermal damage
to nerve endings and diminish the perception of
pain. Also, several recent studies comparing the
laser-facilitated method with other techniques have
shown that less bone formation and bridging occurs
with the laser-facilitated procedure; however, these
studies have been performed in normal horses.
Longer studies and especially studies in clinically
affected horses are needed to determine if this technique is ultimately successful in generating joint
fusion.
In an effort to improve success rates and benefit
from features of multiple techniques, it has recently
been described to combine the intra-articular drilling with diode-laser treatment. It is recommended
to perform the laser-facilitated procedure first followed by the surgical drilling. The drilling should
stimulate more bone production and fusion, whereas
the laser might reduce the post-operative pain.
This combination of procedures has been reported to
have been performed without complications thus
far.
Surgical stabilization in addition to intra-articular drilling of the distal tarsal joints has been proposed to have a superior clinical result versus intraarticular drilling alone. Lag screws or a screw and
plate combination have been used. That study reported a success rate of 89% of horses returning to
soundness compared with 60% with drilling alone.
However, only a small number of cases were reported. Further studies are needed to determine if
surgical stabilization should be recommended as a
means to improve clinical outcome.
Post-operative care includes the use of NSAIDs,
bandaging, and initial stall confinement. Except in
those cases where surgical implants are used, hand
walking commences after bandages are removed in
2–3 wk. During the second month, the patient is
allowed turnout into a small paddock. If responding favorably after 60 days, the horse is allowed to
return to a gradual exercise program. In many
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cases, the horse will be significantly improved in
90 –120 days and may return to competition; however, it usually takes ⬃1 yr for fusion to occur.
In those cases where the distal intertarsal disease
was significantly more advanced than the tarsometatarsal joint, periodic corticosteroid injections of
the tarsometatarsal joint may be beneficial postoperatively for a period of time.
6.
Conclusions
Distal tarsal inflammation and osteoarthritis are
very common conditions in the athletic horse. The
severity of signs are variable but frequently are related to a reduction in athletic performance. Often,
a tentative diagnosis can be made with a corresponding history and supportive clinical signs.
The diagnosis can be confirmed with an appropriate
response to intra-articular anesthesia and radiographic findings. Many horses can be managed
throughout their athletic career with periodic injections of corticosteroid, usually in combination with
hyaluronan. If the clinical response to injections is
less than optimal, then further therapy such as extracorporeal shockwave or surgical intervention
may be necessary. The need for more aggressive
therapy decreases the prognosis for athletic function, although the majority still have a positive
outcome.
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