Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

488 Small Animal Radiolo g y and Ultrasono graphy
lateral or caudal and medial. In addition, the degree of proximal displacement, or overriding,
of fragments; displacement of one fragment into another, or impaction; axial
alignment, varus or valgus; and joint or physeal involvement should be noted
(Fig. 4-15).
Avulsion fractures may result in severe clinical signs by interrupting the function of the
tendons or ligaments that attach to the fracture fragments (Figs. 4-16 to 4-18).
Physeal lines, secondary ossification centers, and irregular ossification patterns may be
mistaken for fractures. Comparison radiographs of the uninjured opposite extremity may
be extremely helpful in evaluating immature patients.
Fractures in immature patients frequently involve the growth plate, or physis. The common
patterns of physeal fractures are classified according to the direction and extent of the
fracture line as described in the following list.
C L A S S I F I C AT I O N O F P H Y S E A L F R AC T U R E S
Type I: Fracture extending through the physis with epiphyseal displacement (Fig. 4-19).
Type II: Fracture extending through the physis into the metaphysis with a triangular
segment of metaphysis accompanying the displaced epiphysis (Fig. 4-20).
Type III: Fracture extending from the joint through the epiphysis, to the physis, and
then along the physis, with displacement of a portion of the epiphysis.
Type IV: Fracture extending from the joint through the epiphysis, physis, and adjacent
metaphysis (Fig. 4-21).
Type V: Impaction, or crushing, injury to physis without displacement (Fig. 4-22).
Any fracture that involves a physis may result in a growth disturbance. The probability
of a growth disturbance increases from type I to type V fractures. 67,68
The growth disturbance that results from physeal trauma varies depending upon the
trauma site, severity of the injury, and the animal’s remaining growth potential at the time
of the injury. 69-76 Lateral deviation of the foot is observed most often in association with
altered distal ulnar and radial growth (see Fig. 4-22). Subluxation of the humeroradial or
humeroulnar articulation or anconeal fracture may occur also (Figs. 4-23 and 4-24).
Because the angular deformity may be corrected more easily if diagnosed early, all animals
with known or suspected physeal trauma, especially radial or ulnar, should be examined
frequently, and radiographs of the affected and unaffected limbs should be compared.
Text continued on p. 494
Fig. 4-15 A 16-month-old female
Irish Setter that was hit by a car and
had left front leg lameness. There is a
fracture involving the proximal ulna
that extends into the joint. There is
only slight displacement of the fracture
fragments. The margins of the
fracture are smooth, and there is a
faint periosteal response on the caudal
aspect of the ulna (arrows). This
is because the fracture was 12 days
old. Diagnosis: Intraarticular transverse
fracture.