Page 694 - Adams and Stashak's Lameness in Horses, 7th Edition

660 Chapter 5

radiographic exam include soft tissue swelling without aspect of the tarsus, it is important to utilize a normal
bony change, fractures, and developmental disorders. range of motion with flexion and extension in an attempt
VetBooks.ir graphic examination of tarsus is bone spavin. This surfaces of the articular cartilage of the joint. This tech-
to evaluate the weight‐bearing and non‐weight‐bearing
The most common clinical condition requiring radio-
nique can also be utilized when evaluating the joint for
arthritic condition of the DT joints manifests a variety
of radiographic changes including osteophytes at the OC and the position and mobility of osteochondral
joint margins of the DT joints, loss of joint space, and fragments predominantly in the dorsal and plantar
the presence of sclerotic tarsal bones, particularly the aspect of the joint. Structures in close proximity that
central tarsal bone. However, joint space narrowing have similar sonographic density can be difficult to sep-
associated with the distal joints caused by bone spavin arate. Detailed descriptions of the US examination of
can be difficult to detect and are best demonstrated with the tarsus exist. 32,35,59,116,140,148
radiographic projections that center the beam on the
lower tarsal joints.
Another common clinical condition requiring radio- Scintigraphic Examination of the Tarsus
graphic examination of the tarsus is OC of the TC joint. Hindlimb lameness that cannot be conclusively
The most common sites for OC in decreasing frequency diagnosed with radiographic and ultrasonographic
of occurrence are the distal intermediate ridge of the examinations may be candidates for scintigra-
tibia (DIRT), the lateral trochlear ridge (LTR), the medial phy. 44,49,59,102,103,119,137 The bone scan technique can
malleolus (MM), the medial trochlear ridge (MTR), and allow detection of subtle bone changes undetected
the lateral malleolus (LM). OC of the TC joint most by other diagnostic methods. DT joint pain is often
commonly manifests as osteochondral fragmentation, associated with increased radiopharmaceutical
but subchondral lucencies and irregularity can also occur. uptake (IRU) in the DT joints compared with that
seen in normal horses. Any acute onset of lameness
Ultrasonography of the Tarsus thought due to a tarsal fracture but without radio-
graphic evidence of a fracture is also a candidate for
Many of the structures of interest in the tarsus are a bone scan. Increased radionuclide uptake does not
superficial and lie just under the skin and subcutaneous always equate with clinical significance, emphasiz-
tissue, and therefore US provides an excellent means ing that interpretation of nuclear scintigraphic
imaging these soft tissue structures (Figure 5.63). A images without reference to the clinical examination
high‐frequency (10–18 MHz) linear probe with variable and other imaging results can be potentially mislead-
focal zones is ideal and can be enhanced when a stand- ing (Figure 5.64).
off works best. A scanning depth of 4–6 cm or less is
appropriate for most structures. The sonographic exam-
ination of the tarsus should be methodically examined Computed Tomography of the Tarsus
from the dorsal (extensor surface), medial, lateral, and CT in the horse is indicated when other bone imaging
plantar (flexor surface) aspects of the joint. These technologies are inconclusive or when there is a fracture
146
areas should initially be examined with the animal that needs more characterization. CT can provide infor-
weight‐bearing, and because diagnostic US has the mation about a bony lesion not available with other
added benefit of providing real‐time information, these imaging techniques. 109,115 Occasionally CT can be useful
structures should also be examined throughout their when other imaging techniques demonstrate tarsal
range of motion. When evaluating the dorsal and plantar lesions and there is a need for better interpretation (like

A B
Figure 5.63. Ultrasonographic images of the normal gastrocnemius attachment to the tuber calcis (A) and the articular surface of the
lateral trochlear ridge of the talus (B).