Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

578 Small Animal Radiolo g y and Ultrasono graphy
and neck that usually is poorly defined. Later, joint space widening followed by a subchondral
radiolucency within the femoral head is seen. Collapse of the cranial dorsal articular
surface with a flattened femoral head and secondary degenerative joint disease ultimately
will occur (Figs. 4-130 to 4-132). The spontaneous disease frequently is bilateral, but the
lesions may not be radiographically apparent at the same time.
A variant of osteonecrosis, which has been described in cats, manifests as unilateral or
bilateral aseptic necrosis and remodeling of the femoral necks (Fig. 4-133). 595-597 Also usually
noted are capital physeal fractures.
Intracapsular femoral neck and capital physeal fractures may result in loss of the majority
or all of the blood supply to the femoral neck or head. Subsequent revascularization will result
in a loss of bone from the intracapsular and extracapsular portions of the femoral neck. Very
little bone production is evident radiographically, because the necrotic bone is reabsorbed
gradually and replaced. This reestablishes the femoral architecture. If a capital epiphyseal fracture
is not reduced surgically, the capital epiphyseal fragment may remain intact within the
acetabulum, with neither bony absorption nor proliferation. Bony proliferation will be
observed on the femoral neck. Secondary degenerative joint disease may result in either case.
Osteonecrosis of the Humeral Head. Osteonecrosis of the proximal humeral head is a
rare finding in small dogs. Radiographically the humeral head collapses and becomes flattened,
and secondary degenerative joint disease results. The scapular glenoid cavity remodels
to conform to the altered shape of the humeral head. 598
Miscellaneous Coxofemoral Conditions. Other coxofemoral conditions that have been
described include luxation, septic arthritis, fracture (including stress fractures), and
invasive synovial hypertrophy. 599-602 Synovial hypertrophy radiographically appears as a
lytic lesion (Fig. 4-134).
Metabolic, Nutritional, and Idiopathic Disorders
Hemophilia. Soft-tissue swelling may be the only evidence of an acute hemophilic
arthropathy. Chronic hemarthrosis will result in secondary degenerative joint disease.
Periarticular periosteal proliferation eventually will develop along with subchondral sclerosis.
The shoulders and elbows are involved more often than are the hips and stifles. In a
study of a group of hemophilic dogs, a narrowed joint space and subchondral cysts were
reported. 428 All dogs were affected by 1 year, with 65% showing evidence of joint disease
by 6 months of age.
Fig. 4-130 An 8-month-old male Miniature Pinscher with
right rear limb muscle atrophy and weakness of 6 weeks duration.
There is mild subluxation of the right coxofemoral joint.
There is increased density involving the femoral neck and proximal
femoral metaphysis, with slight irregularity at the junction
between the femoral head and neck (arrows). Diagnosis:
Osteonecrosis of the right femoral head. These changes are early
in the disease course. The left coxofemoral joint is normal at this
time.