Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

552 Small Animal Radiolo g y and Ultrasono graphy
Fig. 4-100 A 4-year-old male
mixed breed dog had a right rear
limb lameness for 5 months. Soft-tissue
swelling is noted in the stifle
joint (open arrows). There are areas
of irregular bony proliferation on
the proximal and distal margins of
the patella and on the proximal
aspect of the distal femoral articular
surface (closed arrows). Diagnosis:
Mild degenerative joint disease. This
was secondary to rupture of the cranial
cruciate ligament.
Primary degenerative joint disease results from apparently normal wear and tear. No
specific or predisposing cause can be identified. Secondary degenerative joint disease
results from a specific or predisposing condition or event such as those listed below.
●
Trauma (injury to adjacent bone, ligament, tendon, articular cartilage, joint capsule)
●
Conformational or developmental abnormality (abnormal stress or use of the limb
that results from congenital, inherited, or acquired limb deformities)
●
Metabolic, nutritional, and idiopathic disorders (e.g., hemophilia, mucopolysaccharidosis,
hypervitaminosis A, hyperparathyroidism, or congenital hypothyroidism)
●
Neoplastic arthropathy (tumors arising from the periarticular soft tissues)
●
Infectious arthritis (bacterial, mycotic, viral, protozoal, and mycoplasmal arthritis)
●
Immune-mediated arthritis (erosive and nonerosive)
●
Crystal-induced arthritis (includes gout and pseudogout, or calcium pyrophosphate
dihydrate [CPPD] deposition disease)
●
Villonodular synovitis
D E G E N E R AT I V E J O I N T D I S E A S E
Degenerative joint disease, also known as osteoarthritis and osteoarthrosis, is a common
arthropathy with many diverse causes. The radiographic features of degenerative joint disease
are similar regardless of the underlying etiology (Figs. 4-100 and 4-101). 425-429 Softtissue
swelling usually is minimal. Periarticular periosteal proliferation occurs at the sites
of joint capsule and ligamentous attachment and at the margins of the articular cartilage.
This proliferation usually is smooth and uniformly mineralized with well-defined margins.
The subchondral bone may become thinned, thickened, dense, or irregular. Intraarticular
or periarticular bony densities may be seen. These densities may be due to avulsion fractures,
joint capsule or tendinous mineralizations, or mineralization of detached articular
cartilage fragments, known as joint mice or synovial osteochondromatosis. 431,436-467
Narrowing of the joint space and subchondral bone cysts may be observed. Malalignment
of articular surfaces or joint subluxation may be seen with some specific conditions; however,
weight-bearing or stress radiographs may be required to demonstrate joint instability
(Fig. 4-102). 11 In most cases, the radiographic findings are less extensive than those
observed at surgery or necropsy. The more severe the radiographic findings, the poorer the
prognosis despite the correction of any underlying disease. With severe degenerative
changes, the underlying cause may be obscured. The progression of the radiographic
changes usually is slow, with little difference observed over several months.
Primary degenerative joint disease, resulting from normal wear and tear on a joint, is
uncommon in small animals but may be observed as an incidental finding. It typically