Page 745 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Proximal Limb 711

CT offers more potential to image intra‐articular soft immobile OCD fragments may separate, causing sudden
tissues within the stifle than other techniques currently clinical signs in athletes. 27
VetBooks.ir more information on the capabilities of CT and MRI. 2‐ to 3‐year‐olds in training; more than half of a series
The usual age at presentation varies from weanling to
The reader is referred to Chapter 3 for
available.
9,72
of 161 horses were 1 year of age or younger. Training
Arthroscopy remains both a diagnostic and treatment
34
tool for all of the stifle joints. Multiple different tech- may be required to cause clinical signs; presumably the
niques and approaches have been developed, and osteochondral defect becomes disrupted, causing syno-
arthroscopy remains the standard for exploration and vitis. Horses presenting after training has begun gener-
surgical treatment of all three stifle joints without sig- ally have less severe lesions than weanlings or yearlings
nificant risk of incisional complications. 65,76 Arthroscopy that present earlier, which is probably why the older
is the definitive diagnostic tool for problems isolated to group has an overall better outcome after surgery. 34,65
the FP, MFT, or LFT joints that are inapparent with Some horses have radiographic evidence of OCD with-
other types of imaging. 35,64,65,93 Needle arthroscopy in out clinical signs. The clinical significance of the lesion
the standing horse has been advocated to improve char- should be confirmed by intrasynovial analgesia, particu-
acterization of lesions although treatment of lesions larly among horses in active training or older horses
may be limited with this technique. 36 with minimal femoropatellar effusion or radiographic
change. Weanlings with femoropatellar OCD may pre-
sent with joint effusion, lameness, and no radiographic
FEMOROPATELLAR JOINT changes. Horses with OCD lesions that appear on
19
Osteochondritis Dissecans (OCD) radiographs but are not causing clinical signs at the time
should be monitored, especially during early training,
Femoropatellar osteochondritis dissecans (OCD) is a with the goal of considering treatment if they become
very common cause of stifle lameness rivaled in occur- clinically significant.
rence only by that in the tarsocrural joint. 51,63 In one
study, Thoroughbreds were the most commonly affected
of a series of 161 horses having surgery. Seventy‐eight Diagnosis
34
percent were 2 years old and younger (most were year- LM radiographs usually demonstrate a flattened
lings), twice as many males as females were affected, and defect in the proximal portion of the lateral trochlear
they were typically the better individuals in the herd. ridge of the femur where it articulates with the distal
104
Femoropatellar OCD primarily affects the lateral troch- patella (Figure 5.112 and 10.48). Ossification within the
lear ridge. 34,63,64 However, lesions may be located on the defect is variable, and loose bodies may be present. 19,34,64
medial trochlear ridge, the trochlear groove, the articu- Less commonly, deeper ossification defects or subchon-
lar surface of the patella, or in any combination. 34,65 dral cystic lesions may occur, or the defect may be so
large that the patella is unstable (Figure 5.113). 19,64,65
Caudolateral to craniomedial oblique films may provide
Clinical Signs
more information about the severity of lateral trochlear
Femoropatellar OCD usually causes visible joint effu- ridge defects, which may extend over the lateral side of
sion (Figure 5.110) and variable hindlimb lameness. In the trochlear ridge. Patellar changes may be due to pri-
some cases the lesions might be incidentally visualized mary OCD or secondary to irritation from a severe lat-
prior to lameness in horses that are imaged for sale. The eral trochlear ridge lesion, but may not be discovered
lesion is a cartilage or osteochondral defect with separa- until surgery is performed. However, severe patellar
tion, producing synovitis. Subtle effusion can be com- lesions can be observed in the LM view and typically
pared to the contralateral stifle, but at least half of contribute to a worse prognosis (Figure 5.114).
affected horses have bilateral lesions. 34,63 Synovial fluid In one study, radiographically normal areas contained
analysis is usually unremarkable. Uncommonly, horses lesions detectable only by arthroscopy in 40% of 72 FP
93
with stifle lesions may also be affected in other joints; a joints, and more than half had lesions worse than
complete physical exam noting effusion in other joints is anticipated from the radiographs. 19,93 Young foals
indicated. 34,65 Clinically silent OC lesions may be pre- normally have irregular contours of the proximal troch-
sent in other joints, and survey radiographs may be of lear ridges that should not be confused with OC
benefit to best set expectations for clients. (Figure 5.115). 1,44
The lameness may be so mild that joint effusion is the Ultrasound should be considered as an adjunct to
only presenting complaint; however, hindlimb flexion is radiographs as the trochlear surfaces of the distal femur
usually positive in horses with clinically significant are readily visualized using ultrasound. 7,11 In addition,
OCD. Others may be extremely lame, and some young- the LM extent of defects and the trochlear groove can be
sters may have difficulty rising from recumbency. imaged, whereas they may be obscured on radiographs.
Chronic hindlimb lameness in foals may cause second- The sensitivity and specificity of detection of lateral
ary forelimb flexural deformities, which could be the trochlear ridge OCD is quite good. The cartilage on
11
actual presenting complaint in some horses. The severity the lateral trochlear ridge is reported to be thicker than
of synovitis depends upon the lesion itself and the that of the medial ridge. Underscoring the value of
79
amount of inflammation caused by physical activity; exploratory arthroscopy, accuracy on the proximal
the degree of synovitis was not always comparable to medial trochlear ridge is not high for ultrasound or radi-
11
the size of lesions in one report. Uncommonly, the lat- ography. 11,67,93 Although numbers were low, lesions in
eral trochlear ridge defect can be so severe that the the midportion of the medial trochlear ridge were better
patella may luxate laterally. Conversely, previously detected by ultrasound than radiography in one study. 11