Page 766 - Adams and Stashak's Lameness in Horses, 7th Edition

732 Chapter 5

pieces of articular cartilage that may or may not be
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detached from the subchondral bone. Articular carti-
VetBooks.ir can be involved. 9,29
lage fibrillation, erosion, or subchondral bone lysis also
Walmsley has classified the types of articular carti-
lage lesions using human classification systems and in
particular uses the Outerbridge classification for report-
ing. The Outerbridge system grades the lesions on a
scale of 1–4: grade 1 includes softening and swelling of
the articular cartilage, grade 2 includes partial‐thick-
ness defects with fissures on the surface that do not
extend to the subchondral bone and/or do not exceed
1.5 cm in diameter, grade 3 includes fissuring to the sub-
chondral bone and/or a lesion that exceeds 1.5 cm in
diameter, and grade 4 includes those with exposed sub-
chondral bone.
Schneider et al. reported that 6 of 7 horses with focal
Figure 5.133. Subchondral lysis of the medial femoral condyle disease returned to intended use, whereas only 1 of 4
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(arrows) was present on the lateromedial radiographic image of this with generalized condylar damage recovered. Lewis
foal’s stifle. Arthroscopic examination revealed severe articular stated that only 6 of 20 horses returned to intended
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cartilage and subchondral bone degeneration. use. Walmsley et al. found that in horses with
Outerbridge grades 1 and 2, 78% returned to their
intended use, compared with 63% of those with
horse. Adult horses with medial femoral condyle lesions Outerbridge grades 3 and 4. In the study by Cohen et al.,
may or may not have effusion, are usually positive to 60% of horses improved, of which 46% became sound
hindlimb flexion, and respond to intra‐articular analge- and 37% returned to intended use. In general, however,
sia. Although these horses may not respond 100%, any- the severity of articular cartilage lesions was an incon-
thing over 50% improvement is often considered sistent indicator of prognosis (Figure 5.134). 9,30
significant. 29,52 There is no consensus on how best to treat these
Radiographs are commonly unremarkable or only cases. In horses with fibrillation, the fibrillated tags of
show mild OA changes in these horses. Flattening and tissue should be debrided. For those with partial‐thickness
sclerosis of the medial femoral condyle are subtle radio- cracks and erosions, only superficial debridement should
graphic abnormalities that may suggest osteochondral be performed. Some surgeons have proposed using radi-
lesions. However, although flattening is a common ofrequency probes to shrink the involved areas of carti-
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finding, its clinical significance on performance is lim- lage to cause them to recede and theoretically alleviate
ited. Ultrasound is essential to best characterize lesions, loading on the area. This procedure is untested, and in
5
especially to the soft tissue structures such as menisci, human medicine is contentious, because the radiofre-
meniscal ligaments, articular cartilage, and periarticular quency procedure has been shown to cause chondrocyte
tissues. CT with and without contrast can be helpful to death. Lesions with subchondral bone lysis can be lightly
characterize lesions, and MRI is growing in use, allow- debrided. Some cases of full‐thickness erosion have vis-
ing for visualization of most all tissues. Correlation of ible evidence of subchondral bone necrosis that require
imaging findings to disease site, severity, and prognosis debridement. Some surgeons advocate the use of micro-
is contentious. fracture to augment healing; however, in the medial
For horses with equivocal imaging results that block femoral condyle, this procedure could lead to the devel-
to the femorotibial joints, who may or may not have opment of SCL. For the micropick procedure, care must
responded to medication, arthroscopic visualization can be taken to remove all calcified cartilage as failure to do
be beneficial to further characterize the lesions. A stand- so can result in poor healing. The use of mesenchymal
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ing needle scope procedure has been reported and found stem cells along with the microfracture procedure has
useful for characterizing site and severity of lesions. been found to be useful. 16,32
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Therapeutic procedures are often limited with this It is currently unknown why medial femoral condyle
approach, although it can be helpful in determining the lesions occur. Although some think that they may be
need for further conservative versus surgical therapy. developmental in nature, acute trauma and/or chronic
repetitive trauma cannot be ruled out. There is also con-
Treatment cern that flattening or dimpling of the subchondral bone
may predispose these horses to this injury. Contino
Arthroscopic surgery in foals should be preceded by showed that these lesions are common in young Quarter
obtaining a synovial fluid sample for culture and sensi- horses, but there has been no correlation in clinical
5
tivity. Debrided bone also may be submitted. Care studies. Scott et al. found that horses with flattening or
5
should be taken during debridement because the normal mild lysis are likely to have articular cartilage lesions
subchondral bone of foals is soft and easily removed. that require debridement. Of those horses, 7 of 9 with
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Therefore, it is difficult to assess the extent of damage. focal lesions were sound postsurgery compared with
Arthroscopic findings in adults usually include focal 2 of 6 with generalized lesions. Care must be taken,
or generalized articular cartilage lesions (Figure 5.134). however, because overly aggressive debridement and
Focal lesions are usually dimples, wrinkles, or folded microfracture may lead to secondary SCL formation.