Page 297 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

272 CHAPTER 1

VetBooks.ir Differential diagnosis articular facet and the abaxial mammillary process
should be higher than the joint space; an osteophyte,
Other conditions that can cause back pain are
impingement of the DSPs, spondylosis, non-
the mammillary process (Fig. 1.516).
displaced fractures and ligamentous or muscular indicating OA, will make the joint area higher than
pathology. Radiographic imaging of the thoracic facet joints
is easier than in the lumbar area, thanks to the
Diagnosis overlying lung. The normal joint space appears as a
The conventional imaging modalities of radiography radiolucent oblique line sloping from cranial to cau-
(see Fig. 1.484), ultrasonography (see Fig. 1.487), dal at an angle of approximately 45° to the vertebral
and scintigraphy (see Fig. 1.509) can all assist the bodies. On high-quality radiographs, sclerosis of the
diagnosis of dorsal intervertebral facet joint OA. articular facets, subchondral lucencies and periar-
These joints are most easily observed on ultrasound, ticular bone proliferation obscuring the joint space
using a 3–4 MHz curvilinear probe in a parasagit- can be detected (Fig. 1.517). There may be concur-
tal position. The joints are large and horizontally rent impinging DSPs visible on laterolateral radio-
orientated in the lumbar region, making these the graphs, which have a worsening negative effect on
easiest to image in a transverse position. In the tho- the clinical signs and prognosis. Scintigraphy does
racic region they are much smaller and diagonally demonstrate increased bone activity in a propor-
orientated, making a longitudinal orientation more tion of horses. While this undoubtedly increases the
helpful. Osteophytes on the axial aspect of the joint chances that the OA is clinically significant, there is
space indicate OA. In the lumbar area, the cra- still considerable scope for false negatives and error
nial articular facet is more dorsal than the caudal when used in isolation.

1.516
T18

Fig. 1.516 Transverse parasagittal
ultrasound images of arthritic lumbar
facet joints at T18/L1 using a 4 MHz
curvilinear probe. Osteophytes have
formed on the joint (arrow), making
this higher than the abaxial edge of the
mammillary process of T18 (arrowhead).
Compare with normal in 1.487.

1.517

Fig. 1.517 Ventrolateral 20° to
dorsolateral oblique radiograph of
the caudal thoracic region of a horse
with facet joint disease. Sclerosis
of the articular facets, subchondral
lucencies and periarticular bone
proliferation obscuring the joint space
can be detected (arrows). Compare with
normal in 1.484.