Page 711 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 677

release of biochemical/inflammatory and physical debris
into the joint. Continual shedding of biochemical and
VetBooks.ir synovial effusion or thickening of the fibrous joint cap-
physical substances into the joint can lead to chronic
sule of the joint. In sites other than the DIRT, the OCD
lesions often remain loosely attached in their bone of
origin, but the debris that is released into the joint from
beneath the flap results in synovitis or joint inflamma-
tion. Occasionally an OCD fragment is made entirely of
cartilage and cannot be identified on radiographs. The
radiolucent defect left in the parent bone may be all that
is apparent in many cases. If the OC and cartilage flap is Figure 5.77. Osteochondrosis lesions can also be accurately
more chronic, then the cartilage flap may begin to ossify identified on ultrasound examination as an irregularity to the
and be radiographically apparent. In contrast, some subchondral surface, as thickening of the articular cartilage, and
older horses are diagnosed with OCD incidentally with- occasionally as a calcifying flap separating from the subchondral
out apparent clinical signs. surface (arrows) as demonstrated in this transverse ultrasound
The radiographic abnormalities associated with OC/ image of the lateral trochlear ridge.
OCD include fragmentation; irregular, flattened contour
of the subchondral bone surface, with or without sub- risk of maturing or increasing in size. The earlier the OC
chondral radiolucencies and/or sclerosis; and occasion- is removed, the more likely the effusion and joint cap-
ally secondary OA. DIRT lesions are best visualized on sule swelling will resolve, although not all horses with
the DM‐PlLO projection. Lesions of the trochlear ridges OC of the tarsus require surgery. Horses with small
may be evaluated on the DM‐PlLO (lateral ridge), DL‐ lesions, with minimal effusion, and without lameness
PlMO (medial ridge), or LM projections. OC of the may not require surgery particularly if they are pleasure
MTR is rare and must be differentiated from the normal horses or light use horses. However, loose flaps and
variably sized protuberance of this ridge, where normal large areas of abnormal cartilage and subchondral bone
spurs and fragments can occasionally be seen. 23,27 Free can lead to persistent inflammation in the joint and over
fragments seen in the dorsal aspect of the joint can origi- time may lead to the development of OA. If significant
nate from the trochlear ridges (usually at the distal degenerative changes of the articular cartilage are identi-
aspect of the LTR) but can also originate from the DIRT fied at surgery, the prognosis for the return to soundness
area. OC/OCD of the MM is best demonstrated with is less favorable.
137
a DPl or DL‐PlMO projection and must be differenti- Treatment of choice for OCDs of the TC joint is
ated from avulsion fractures of the CLs. Flexed projec- arthroscopic removal of the fragment and debridement
tions may be useful to demonstrate loose fragments in of the damaged cartilage and subchondral bone. The
the plantar recesses of the TC joint or OC lesions in the removal of the OCD lesion surface (unstable articular
proximal trochlear ridge. 17,104 surface) stops the inflammatory process within the par-
Radiography often underestimates the extent of the ent bone and eliminates the shedding of debris into the
cartilage and bone damage that is later identified at sur- joint. If surgical removal of the fragment(s) and debride-
gery, particularly for LTR lesions. The TC joint can ment of the parent bone occurs before permanent dam-
manifest radiographically silent lesions (lesions iden- age to the articular cartilage occurs, the prognosis is
tified at surgery where no abnormality was seen on excellent for resolution of the synovial effusion and res-
radiographs) more commonly than in other joints. toration of normality to the joint. 92,94 Fortunately OCD
Occasionally, purely cartilaginous loose bodies that are of the TC joint often occurs at sites that are easily accessible/
not seen radiographically can be well identified using amenable to surgical removal and debridement.
arthroscopy. 17 Osteochondral fragmentation of the distal aspect of the
The use of diagnostic US should be considered in the MTR is not often a surgical problem as it is usually
evaluation of tarsal OC to complement radiography. within the synovial attachment of the TC joint capsule.
Diagnostic US can be a very useful tool to help evaluate Because the OC lesion is embedded within the synovium,
the thickness of the articular cartilage and the surface of it does not shed debris within the joint and rarely
the subchondral bone plate (Figure 5.77). It can also becomes a clinical problem.
help provide valuable information about the joint envi- The clinical significance of DIRT lesions and the
ronment (synovial membrane, synovial fluid, articular effect they have on performance have often been ques-
cartilage, and subchondral surface) in any horse with tioned. There appears to be little apparent influence on
10
joint effusion. Diagnostic US can be particularly useful performance of the young Thoroughbred racehorse.
in cases where OC is suspected, but the radiographs are Comparisons between the racing performance of horses
inconclusive. This examination of the joint can be quite with TC OC treated conservatively and those without
useful to help determine the primary site of OC and to TC OC were unable to demonstrate any significant dif-
assess the size and the extent of the lesion before ferences in the lifetime racing performance. More sub-
22
surgery. jective influence on performance may exist in more
Resolution of the effusion generally requires surgery mature performance horses. Historically, DIRT lesions
and the removal of the abnormal tissue. In the tarsus, that were found in sport horses on prepurchase or on
surgery can be considered early after the recognition of routine radiographic examination of the tarsus were left
the OC assuming the foal is older than 7 months of age. in situ provided they were not creating effusion or lame-
Unlike stifle lesions, OC lesions in the tarsus are not at ness. However, it is not uncommon to have these horses