Page 698 - Adams and Stashak's Lameness in Horses, 7th Edition

664 Chapter 5

DT joint OA often occurs bilaterally, but occasionally the accuracy of diagnostic analgesia may be questioned
it may occur unilaterally. There is often a history of based on the potential for leakage of local anesthetic
VetBooks.ir eral DT joint pain may not manifest overt lameness but around the insertions of the cranial tibialis (CT) and
around the proximal plantar metatarsus and extension
gradual onset of lameness. Occasional horses with bilat-
peroneus tertius (PT) tendons following injection of the
may be thought to have a behavioral issue or a lack of
performance. When lameness occurs, it may become TMT joint. The injection of contrast media into the DT
worse when the horse is worked hard for several days joints of the tarsus demonstrated that once the media
and may improve with rest. Lameness tends to be worse filled the joint space, there was extension of fluid sur-
when the horse is first started into work. Many mildly rounding the proximal plantar metatarsus and origin of
affected horses tend to warm out of the lameness after a the SL in 70% of the limbs. One study found that
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short time. The horse may feel stiff or jerky when circled forced injection into the TMT joint caused rupture and
to the affected side, and it may refuse or be reluctant to extra‐articular leakage of contrast around the head of
go in the opposite direction or take the opposite lead. the lateral splint. Leakage was found to occur close to
80
However, some horses show more lameness with the the area of the lateral plantar nerve and DBLPN, poten-
lame or lamer limb on the outside. Western performance tially leading to false‐positive responses. In addition, the
horses (i.e. reining, roping, and cutting) or gaming variability of communication between the TMT and
horses that are required to stop aggressively can become DIT joints 11,42,80,121 suggests that these joints should be
reluctant to decelerate or perform sliding stops required anesthetized separately.
for their discipline. An animal may develop a problem The TMT joint is the easiest joint to inject and is
with the performance of discipline‐specific maneuvers approached plantaroproximal to the base (head) of the
such as refusing to jump or to jump poorly with an fourth metatarsal bone. The site for injection of the DIT
increase in rails knocked down. The horse may have joint is from the dorsomedial aspect of the limb distal to
trouble picking up or holding a lead or may show a the palpable distal border of the medial branch of the
reluctance to turn in one direction. The development of tendon of the tibialis cranialis muscle (cunean tendon)
these types of performance or behavioral issues can be and between the central, third, and combined first and
consistent with the development of DT joint pain. second tarsal bones. In the normal horse this may be dif-
The way in which horses with DT joint pain manifest ficult to accurately palpate, making is difficult to com-
lameness can vary considerably. Some clinicians have fortably inject this joint. Many clinicians prefer to inject
reported a tendency for horses with DT joint pain to the TMT joint first with 2–3 mL of mepivacaine until
manifest a characteristic limb carriage and foot place- resistance is felt. Any more pressure increases the risk of
ment. This gait can be described as an axial deviation of anesthetic solution escaping the joint capsule. When
limb during the swing phase of the stride with a rapid communication between these two joints exists, needle
abaxial deviation of the limb just before contact with placement into the DIT may allow for observing of local
the ground (so‐called J‐step). While this limb carriage is anesthetic dripping out of the needle. The clinician
common in horses with DT pain, it is not pathogno- should interpret this carefully as the needle may easily
monic. In addition the horse with DT joint pain can enter the TMT joint if it is placed too far distally in the
have a reduced degree of flexion of the hock during the space between the third and second tarsal bones. When
swing phase of the stride. This translates into a reduc- communication of these joints is found to exist, treating
tion in the height of the foot flight arc and a shortening only the TMT joints may prove to be effective at ade-
of the cranial phase of the stride often with an associ- quately managing DT (both DIT and TMT) joint pain.
ated dragging of the toe. Lameness associated with DT That may not be the case once the pathological process
pain may include asymmetrical movement of the tubera progresses and begins to occlude or obstruct this com-
coxae, shortening of the cranial phase of the stride, and munication. Interpreting the results of intra‐articular
sometimes a reduced extension of the fetlock during analgesia of the DT joints may prove to be difficult.
stance phase. In addition the affected limb usually lands Intra‐articular analgesia may only improve the lameness
toe first, resulting in excessive wearing of the toe. score by 50% due to moderate to advanced osteoar-
Kinematic gait measurements recorded after endotoxin‐ thritic and coexistent subchondral bone pain.
induced lameness of the DT joints were considerably Improvement is generally seen within 20 minutes, but
different than what occurs clinically in horses with bone occasionally the response is delayed. Some clinicians
spavin. This study reported that fetlock and tarsal recommend delaying further blocks until at least 1 hour
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joint extension decreased during stance phase, fetlock has elapsed.
joint flexion and hoof height during swing phase Moderate to severe OA with proliferative periarticu-
increased, and vertical excursion of the tuber coxae lar bone can make placing a needle into a narrowed
became more asymmetrical. 79 joint space difficult if not impossible. In these cases radi-
ographic and US‐guided control may be required to
assist needle placement into the joint space. When intra‐
Diagnostic Analgesia
articular analgesia is too difficult or ineffective at elimi-
Flexion tests of the hindlimb have low specificity nating lameness of the DT joints, perineural analgesia of
(multiple joints are flexed at the same time), which the superficial and deep peroneal (fibular) and the tibial
emphasizes the need to utilize diagnostic analgesia to nerves should be utilized. Blocking of the caudal tibial
confirm the source of lameness. Accurate placement of and deep peroneal nerves is a reasonably accurate diag-
the intra‐articular anesthesia of the TMT and/or DIT nostic method. However, other structures in addition to
joints should be performed in many horses to confirm the DT joints are blocked, and the effect of this block
that the origin of the lameness is the tarsus. However, may not be complete. Further, confirmation of complete