Page 712 - Adams and Stashak's Lameness in Horses, 7th Edition

678 Chapter 5

develop synovitis and lameness later in their career. To
appropriately manage these horses, the fragments should
VetBooks.ir ent with OA is often found at time of surgery, and some
be removed arthroscopically. Cartilage damage consist-
of these horses can be difficult to keep sound because of
persistent low‐grade lameness. It has previously been
suggested that older show jumpers may dislodge inter-
mediate ridge fragments resulting in acute lameness.
Based on these experiences, it may be advisable to
remove potentially mobile fragments in the TC joint
because of the potential for horses to develop OA as
mature performance horses.
In young horses the prognosis for athletic activity
after surgical removal is good. TC effusion resolved after
surgery in 89% of racehorses and 74% of nonracehorses.
Effusion appears to be less likely to resolve if the lesions
were on the LTR or MM. However, there appears to be
no correlation between resolution of effusion and ath-
letic performance. Lesion location and unilateral vs.
bilateral lesions had no effect on ability to start. Although
the trend was present in all groups, only 2‐year‐old
Standardbreds were significantly less likely to start a race
when multiple sites within the TC joint were affected. 12

Proximal Intertarsal Joint Synovitis and OA
Loose fragments, usually shed from the intermediate
ridge of the distal tibia, can become lodged in the dorsal
pouch or dorsal joint capsule of the PIT joint. Although
rarely of clinical significance, these fragments can be
removed arthroscopically through the TC joint if consid-
136
ered necessary. Because of their limited clinical signifi- Figure 5.78. Loose fragments (arrows) usually shed from an
cance and the relative difficulty of finding and removing OCD lesion on the distal intermediate ridge of the tibia can become
the fragments, it has been recommended that they be lodged in the dorsal pouch or dorsal joint capsule of the PIT joint.
removed only if this can be easily accomplished during Although rarely of clinical significance, these fragments can be
surgery for the primary lesion of the TC joint (Figure 5.78). removed arthroscopically through the TC joint.
Synovitis/osteoarthritis of the PIT joint is usually due to
progression of DT OA but can also occur from external
trauma. Radiographic signs of PIT OA are very similar to developmental failure of endochondral ossification, (2)
those of the distal joints and are usually more prevalent acquired and caused by some form of cartilage injury
on the medial aspect of the tarsus (Figure 5.79). and subchondral bone trauma and (3) due to an infec-
tious cause. SCLs occur in younger animals and are
thought to be related to OC lesions that occur at sites of
Subchondral Cystic Lesions (SCLs) major weight‐bearing. Compressive loads on an OC
98
SCLs are typically seen in young horses but can occur lesion can lead to a further weakening of the subchon-
in any aged animal. 55,69,71, 98 Not all horses with SCL are dral bone and formation of SCLs. Mature animals can
lame and many can be clinically quiescent. Cystic struc- develop SCLs potentially from some form of mechanical
tures associated with the tarsus have occurred in the trauma. A supraphysiological load on a normal articular
MTR or LTR of the talus, the intertrochlear groove, the surface may initiate sufficient bone injury that can lead
MM or LM, DIRT, distal aspect of the tibia, calcaneus, to the creation of an SCL. The hydraulic theory assumes
CT, T3, and proximal MT3 (rare). SCLs are character- the formation of SCLs is caused by joint fluid being
ized by radiolucent areas of bone (from several millim- forced into a cartilage defect. Infection is known to
eters up to and even larger than 3 cm) and are often cause SCLs in many locations in young animals.
accompanied by a thin, but well‐demarcated, sclerotic The standard radiographic examination of the tarsus
rim (Figure 5.80). The cysts can be uni‐ or multi‐locu- may not adequately demonstrate SCLs because of their
lated and may or may not communicate with the joint. small size and position within a complex joint.
Lesions that are close to or involve the articular surface Nonstandard radiographic views may be necessary to
are more likely to cause lameness. Lameness associated document these lesions. When visible, an SCL appears as
with SCL is believed to be the result of synovitis and a discreet radiolucency varying in size and shape but
increased intracystic or intraosseous pressures leading often surrounded by a sclerotic border. Advanced diag-
to subchondral bone pain. However, it is unclear why nostic imaging modalities such as CT and/or MRI that
some SCLs are asymptomatic. represent the limb in cross section are ideal to document
There are three predominant hypotheses about the their location but not always practical as they require gen-
possible etiology for SCLs in the tarsus: (1) related to a eral anesthesia. Scintigraphic examination can be helpful