Page 697 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 663

potentially excessive tension on the attachment of the walk and trot in a straight line and circle as well as a
major dorsal ligaments. It has long been thought that canter in a circle. If possible, watching the horse being
VetBooks.ir affected joints, which then progress dorsally. However, demonstrating the lameness that the owner/trainer has
ridden can be very useful and may be most effective at
DT joint pain begins on the dorsomedial aspect of
described. When the opportunity exists, the horse can be
Dyson has reported that DT joint OA initially manifests
radiographic and scintigraphic abnormalities on the examined with a rider up and comparisons made about
dorsolateral aspect of the joints. 40,43 the gait before and after intra‐articular diagnostic anal-
OA of the DT joints commonly affects athletic horses gesia is performed.
during the most productive years of their lives and can Physical examination can be confusing and reveal pain
limit career length. 7,17,24,43,56,57,99,100,138 The pathogenesis and sensitivity through the back and pelvic regions. These
of spavin can be divided into three phases: (1) fibrilla- clinical findings may give the impression that lameness
tion of cartilage, (2) osteolysis, and (3) ankylosis. The originates from the topline or more proximal on the limb.
first stage can be observed in young horses and can pre- Some horses with DT joint pain manifest a lower arc of
dominantly be found at two predilection sites on the the foot flight and toe dragging with wear patterns devel-
articular cartilage of the DIT joint. The lesions can then oping on its dorsal edge of the toe. In addition, some may
progress further in the direction of the subchondral manifest a change in foot conformation due to an altera-
bone plate where osteolytic lesions may develop. In this tion in how the horse loads the foot. In acute cases of
phase, horses commonly start to show clinical signs of moderate lameness, the application of hoof testers should
lameness. In some cases, the lesions may proceed further be performed to rule out the presence of foot pain before
until a complete ankylosis occurs. The degree of osteoly- evaluating the rest of the limb. Some lamenesses may
sis may significantly influence whether diagnostic anes- involve multiple structures, so it is critical to develop a
thesia will be effective at eliminating the lameness or routine examination protocol that evaluates the entire
provide only partial improvement. Dyson classifies horse while concentrating on the affected limb.
43
horses with DT pain into three categories: (1) horses Joint distension is not a typical sign of OA of the DT
that respond to IA analgesia of either the DIT or TMT joints, because the tarsal retinaculum over these small
joints or both, but with no detectable radiological joints prevents its detection. However, changes in the sil-
abnormality; (2) horses with predominantly periarticu- houettes of the hock may develop medially. This can be
lar osteophyte formation; and (3) horses with joint space due to soft tissue change such as with cunean bursitis
narrowing, subchondral bone lysis, and sclerosis. and/or effusion of the cunean bursa. However, this
However, these three categories are not necessarily con- change in shape is more often due to a firm bony swell-
sidered continuums of OA of the distal tarsus. OA also ing associated with more advanced stages of DT OA.
has been associated with increased intramedullary pres- Palpation of the horse may also demonstrate soreness of
sure particularly within the cuboidal bones of the tarsal the epaxial muscles in the lumbar region and sometimes
region. the caudal gluteal muscles. A compensatory forelimb
In some breeds such as the Icelandic horse, there lameness may also develop due to a reluctance of the
appears to be a genetic component to development of horse to bear appropriate weight on its hindlimbs.
OA in the DT joints. While heritability can be difficult to Physical examination may not reveal any obvious
prove, there has been a very obvious decrease in preva- abnormalities. Palpating the tarsal region may reveal
lence of bone spavin in the Royal Dutch Warmblood irregularity over the dorsomedial aspect of the tarsus,
Studbook (KWPN) due to a strong and consistent selec- but often this is not sensitive to digital pressure. Some
tion process. Selection was based on two main criteria: clinicians may perform a manipulation called Churchill’s
7
conformation and a reduction in radiographic signs of test, which is accomplished by directing digital pressure
bone spavin. It has also been shown in the Dutch over the head of the medial splint as a reflection of DT
Warmblood that there is a strong relationship between a pain. The test is considered positive when the horse
faulty conformation in the hock region (sickle hocks but abducts the limb away from the pressure. The lameness
also extremely extended hocks and abnormal outward examination should begin with a flexion test of the least
rotation during the stance phase) and the occurrence of affected hindlimb first, because the more severely
bone spavin. Animated gaits (such as seen with American affected limb may remain lame after flexion, which can
Saddlebred and Tennessee Walking Horse) can also con- complicate the rest of the lameness exam. The disease is
tribute to the development of bone spavin in these often bilateral, and flexing the unaffected limb may be
horses. For example, the rack is a fast four‐beat gait quite positive or it may cause the hindlimb gait to even
during which the horse places their hindlimbs extremely out because the pain is distributed more evenly behind.
far forward. Proximal and distal limb flexion test should be per-
formed separately. The proximal limb flexion test or
spavin test is useful at accentuating lameness with tarsal
Diagnosis
joint pain in most affected horses. However, a positive
The diagnosis of distal limb/tarsal disorders of the response is not specific for the tarsal lameness because
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hindlimb can be challenging. Frequently clinical signs the reciprocal apparatus creates flexion of tarsus, stifle,
are not obvious and not specific to the tarsus. Structures and coxofemoral joints (to varying degrees) simultane-
in the distal limb and tarsus should be palpated while ously. A stifle flexion test may be utilized to help differ-
standing on the limb and with the limb raised. entiate lameness originating from the tarsus vs. the stifle.
Manipulation of the limb by flexion, extension, and Many horses with proximal limb involvement may
rotation may provide some indication of joint(s) involve- respond positively to both distal and proximal limb
ment. A moving examination should be performed at a flexion.