Page 696 - Adams and Stashak's Lameness in Horses, 7th Edition

662 Chapter 5

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A B
Figure 5.66. Sagittal PD (A) and transverse PD (B) MR images of the tarsus demonstrating normal soft tissue and bone anatomy. MRI is
an extremely useful tool for detection of many types of pathology within the tarsus.

pain revealed variations in subchondral thickness com- has done much work. This is likely due to developmen-
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pared with horses without histories of DT pain. tal lesions of the DT bones (i.e. OC) such as cuboidal
There are few reports on the incidence of MRI diag- bone hypoplasia that is seen in premature and dysma-
noses in the tarsus of live horses. In one cadaver study, ture foals that causes collapse of the central and third
MRI was more sensitive and specific than radiography tarsal bones. 2,3
for detection of all types of pathology of the DT joints, Performance horses in a variety of disciplines and of
including intertarsal ligament pathology, cartilage ero- all ages can develop lameness associated with the DT
sion, osseous cyst‐like lesions, and subchondral bone joints. The DIT and TMT joints are considered the joints
irregularity. In live horses with lameness associated with of the hindlimbs most likely to develop OA from work‐
the tarsal region, the presence of abnormal STIR signal related stress (wear and tear). There are certain types of
hyperintensity compatible with the presence of bone activities that may contribute to uneven or excessive
bruising was reported in the central and third tarsal loading of the lower hock joints. These include sports
bones, talus, and tibia. MRI of the tarsus has also been that require a great deal of hock flexion (dressage),
helpful to diagnose abnormalities that are not identified stress (jumping), sudden stops or turns (western events,
with other imaging modalities. These abnormalities such as reining), or a great deal of concussion
have included subchondral bone injury of the talocalca- (Standardbred [STB] racing). In addition, OA of the DT
neal joint, bone bruising of the distal tibia, intertarsal joints can occur relatively frequently in mature horses
ligament enthesopathy with associated bone edema, that are ridden at a gallop and canter. While bone spavin
focal OA in the plantar aspect of the DIT and talocalca- is seen frequently in mature sport horses used for a vari-
neal joints with localized loss of joint space and sub- ety of disciplines, it is also found as a source of lameness
chondral bone sclerosis, desmitis of the CLs of the TC in young Thoroughbred (TB) and STB racehorses. Bone
and the PIT joints, and tendinitis of the deep digital spavin often occurs in normally conformed horses.
flexor tendon (DDFT) at the level of the calcaneus. There are however some conformational abnormalities
such as sickle hock, cow hock, or excessive straightness
of the hindlimbs that may predispose to DT joint pain.
ARTICULAR DISEASES OF THE TARSUS These types of conformations are felt to produce greater
stress in the medial aspect of the tarsal joint.
Osteoarthritis (OA) of the Distal Tarsal (DT) Joints/DT
Joint Pain Etiology
DT OA has been recognized as a cause of hindlimb OA of the DT joint (bone spavin) typically involves
lameness for centuries. It is frequently called bone or the TMT and DIT joints but occasionally may extend
jack spavin or occult or blind spavin in the absence of into the PIT and TC joint. DT OA is common in a wide
radiographic abnormalities. Chronic cases often develop variety of disciplines probably because these events
an enlargement over the medial or dorsomedial aspects cause increased torsional and shear forces on the DT
of the DT joints. In addition, the term juvenile spavin joints. Many feel that excessive compression and rota-
has been used to describe the development of DT OA in tion of the DT joints during training and competing cre-
horses less than 3 years old typically before the animal ate abnormal tension on the intertarsal ligaments and