Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

556 Small Animal Radiolo g y and Ultrasono graphy
Fig. 4-105 A 4-year-old Cocker Spaniel was hit by a car and became
acutely lame in the right forelimb. There is a complete disruption of
the elbow with the radius and ulna displaced laterally. No fractures
are noted. Diagnosis: Lateral luxation of the right elbow.
tendon attachments; joint space collapse; or malalignment of bones are indicative of softtissue
injury (Figs. 4-106 to 4-108). Weight-bearing or stress radiographs may be required
to demonstrate the extent of the joint instability. In most cases of joint trauma, secondary
degenerative joint disease will occur despite treatment.
Complete or partial tearing of the cranial cruciate ligament is the classic model for secondary
degenerative joint disease. 441-467 Radiographically, the development of the arthritis
occurs in phases.
In the early phase (e.g., first 2 to 3 weeks), the primary change is joint capsule distention
and thickening, typified by anterior and distal displacement of the infrapatellar fat pad
as seen on the lateral projection of the stifle (see Fig. 4-100). The second phase reveals the
emergence of periarticular osteophytes on the femoral epicondyles, the trochlear ridges,
and the medial and lateral tibial plateau regions (see Fig. 4-101). During this phase the
medial collateral ligament will become thickened, so-called medial buttressing, which is best
seen in the anteroposterior or posteroanterior views (see Fig. 4-101). An enthesiophyte,
mineralization of the origin or insertion of a ligament or tendon, will develop cranial to the
tibial intercondylar eminence and is best visualized on the lateral view (see Figs. 4-100 and
4-101). This enthesiophyte is at the location where the cranial cruciate ligament and the
anterior meniscal ligaments attach. Proliferation at that site indicates stress on the ligamentous
attachments.
Most joint luxations are accompanied by ligamentous injury. Small avulsion fractures
may be evident. These fragments should be identified because they reflect the extent of the
soft-tissue injury and affect the patient’s prognosis. With coxofemoral dislocations, avulsion
fractures may occur at the fovea capitis due to ligamentum teres rupture. These fragments
and the associated soft-tissue injury can complicate reduction of the dislocation.
Chip fractures of the acetabular rim also may be observed. Preexisting joint diseases (e.g.,
hip dysplasia) should be recognized because they may complicate reduction of the
dislocation.
Sacroiliac luxations may accompany pelvic trauma. The width of the sacroiliac joint is
a poor sign of sacroiliac luxation. Alignment between the ilium and sacrum is best judged
by tracing the medial aspect of the ilium from the acetabulum cranially to the point at
which it joins the sacrum. The margins should be continuous (Fig. 4-109). Deviation or
malalignment at the junction point indicates sacroiliac luxation. Fractures of the sacrum
or ilium may be present; however, luxation without fracture is more common.