Page 482 - Adams and Stashak's Lameness in Horses, 7th Edition

448 Chapter 4

to assess most horses with navicular disease/ syndr
ome. 20,39,41,43,44,78,100,101 The different sequences permit
VetBooks.ir within the digit in near anatomic detail. The MRI tech-
accurate evaluation of soft tissues, cartilage, and bone
nique can be performed in both the standing (low‐field)
and recumbent (high‐field) patient, but better‐quality
images are thought to be obtained with high‐field units.
The ability to image and appreciate pathologic changes
to articular cartilage and subtle soft tissue and bone
abnormalities is thought to be superior with high‐field
vs. low‐field MRI. 3
Numerous pathologic entities have been identified
with MRI in horses with navicular disease/syndrome,
and many horses appear to have multiple abnormalities
present within the same foot. 38,39,44,78,101 The most com-
mon abnormalities found on MRI involve the navicular
bone, CSL, DSIL, DDFT, navicular bursa, CL of the DIP
joint, and the DIP joint. 38,39,42,44,78,100,101 Several studies
have documented that the DDFT and podotrochlear
apparatus can be abnormal in horses with foot pain
Figure 4.12. An avulsion fracture from the distal border of the (Figure 4.13). 39,43,44,78,100,101 Injury to the DDFT, with a
navicular bone (arrow) can be seen on this lateral radiograph.
reported prevalence of 30%–64% in horses with foot
lameness, is thought to be the most common soft tissue
horses found an overall poor agreement between IRU injury causing lameness in the horse’s foot. However,
106
and a positive diagnosis for lameness and poor perfor- the frequency of occurrence of other soft tissue lesions
mance. For these reasons, and the economics of per- such as those of the CSLs and the CL of the DIP joint
93
forming multiple advanced imaging techniques on the differs among studies. 39,43,44,100,101 This may represent dif-
same horse, MRI is usually performed instead of scintig- ferences in the population of horses of the different
raphy in most horses with foot‐related lameness. studies or possibly differences in the interpretation of
the MRI. From a clinical viewpoint, one difficulty with
interpreting the results of MRI is determining what the
Computed Tomography (CT)
primary abnormality may be when multiple lesions are
CT is thought to be the best modality to detect and found. However, this may be less important if we now
assess pathology within the cortex and trabeculae of the assume that multiple abnormalities within the foot most
navicular bone. 91,96,118 Many osseous changes seen on CT likely contribute to the overall pain in horses with navicular
are not radiographically evident, such as shape changes disease/syndrome. See Chapter 3 for further information
within the bone, distal border fragments, and intramedul- on MRI.
lary changes. 96,118 Soft tissue abnormalities within the foot
may be detected with CT, but in general, CT is best at
detecting abnormalities within bone and MRI is preferred Treatment
to assess soft tissue lesions. However, contrast‐enhanced Multiple factors are involved when deciding on a
131
CT has been shown to improve the imaging of soft tissue treatment protocol for horses with navicular disease/
structures within the foot and may be an alternative to syndrome. In most cases the treatment must be tailor‐
using MRI. 89,91,125 Studies have suggested that the frequency made for each individual horse based on the severity of
of soft tissue injury identification with CT and MRI may lameness, intended use of the horse, wishes of the owner,
be similar, 19,125 and using contrast‐enhanced CT has been results of diagnostics (or lack of diagnostics such as
shown to compare favorably to MRI for identification of MRI), hoof conformation, previous treatments, and
DDFT lesions within the foot. 90,92 Additional advantages most likely diagnosis.
to using CT include decreased anesthesia time since CT Realistically, horses with advanced radiographic
scans are very fast. The use of CT could facilitate an earlier abnormalities in the navicular bone will be problematic
and more accurate diagnosis of navicular bone pathology regardless of the treatments employed. Historically,
in horses but may not be able to detect the many concur- horses with minimal radiographic abnormalities of the
rent soft tissue abnormalities that are often present in navicular bone were thought to respond to therapy
horses with foot pain. However, new advances in CT better than those with radiographic abnormalities.
96
115
technology such as the equine positron emission tomography However, this generalization is debatable because horses
(PET) CT may further enhance the ability of CT to document with DDFT injuries with or without navicular bone
soft tissue pathology within the foot and elsewhere. 89,91 abnormalities tend to do poorly regardless of treat-
See Chapter 3 for further information on musculoskeletal ment. 41,96,106 In addition, developing a treatment proto-
CT imaging. col for horses without radiographic abnormalities and
without performing an MRI can be challenging because
a definitive diagnosis is difficult to make in these horses.
Magnetic Resonance Imaging (MRI)
The ability to develop a more precise treatment protocol
MRI has become increasingly available in recent is considered one of the benefits of performing an MRI
years and is currently the preferred diagnostic technique in horses with foot pain. Using MRI to create an