Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

Chapter Four The Appendicular Skeleton 581
Mucopolysaccharidosis. Bilateral subluxation of the coxofemoral joints with valgus
deformity of the femoral heads and shallow acetabula has been described in association
with mucopolysaccharidosis VI in cats. Other skeletal deformities may include epiphyseal
dysplasia, fusion of cervical vertebrae, flaring of the ribs at the costochondral junctions,
osteoarthrosis of the vertebral articulations, and sternal deformities. 603-605 These findings
are an aid in distinguishing this disease from other causes of secondary degenerative joint
disease. Mucopolysaccharidosis I also has been described, and it appears similar to
mucopolysaccharidosis VI, except that epiphyseal dysplasia of long bones is not seen. 606
Mucopolysaccharidosis II (Hunter’s disease) has been reported in a Labrador Retriever. 607
Hypervitaminosis A. Ankylosis of joints associated with extensive periarticular softtissue
mineralization has been associated with hypervitaminosis A in cats. 338,339,608 Lesions
occur at points of ligamentous and tendinous attachment to the bone, especially in the
periarticular areas (see Fig. 4-82). Periarticular osteophytes are observed most often
around the elbow and shoulder, while involvement of the stifle, hip, and carpal and tarsal
joints is rare. The periarticular osteophytes are smooth and evenly mineralized and tend to
coalesce and bridge the affected joint. The dietary history and presence of lesions in the
vertebral column will help to confirm the diagnosis.
Hypothyroidism. Congenital hypothyroidism has been described in dogs and cats.
Although the retarded bone development that has been observed could result in limb deformity
and subsequent secondary degenerative joint disease, this has not been described.
Hyperparathyroidism. Hyperparathyroidism, either primary or secondary, may produce
secondary degenerative joint disease as a result of limb deformity. Degenerative joint
disease has not been reported as a direct result of hyperparathyroidism.
Neoplastic Arthropathy. Although rare, tumors may originate from the periarticular
soft tissues and invade the joint. Synovial sarcoma is the most common tumor of this type,
although chondrosarcoma, fibrosarcoma, lymphosarcoma, undifferentiated sarcomas, and
others are observed. 219-223 The stifle or elbow is involved more frequently, although any
joint may be affected. Soft-tissue swelling will be identified in all cases. This frequently
extends beyond the anatomical limits of the joint. Soft-tissue mineralization is uncommon.
A small amount of periosteal proliferation may be present at the margins of the lesion. The
predominant radiographic finding usually is destruction of the bones of the affected joint.
Bony destruction begins at the sites of periosteal and ligamentous attachment, but eventually
the subchondral bone will be involved also.
Because joint neoplasms occur in older dogs, they may be superimposed on preexisting
degenerative joint disease and some difficulty may be encountered in recognizing the
presence of a tumor. The irregularly shaped, localized soft-tissue swelling and bony
destruction should not be overlooked if the joint is evaluated carefully, despite the presence
of degenerative joint disease (see Figs. 4-60 and 4-61).
Infectious Arthritis. Joint infection is uncommon in dogs and cats. It may result from
hematogenous spread to the synovial membrane or synovial fluid or direct joint penetration
from a contiguous soft-tissue or bone infection, external wound, surgical procedure,
or intraarticular injection. 609-614 Bacterial infection is encountered most often, although
fungal, viral, mycoplasmal, and protozoal infections have been described. 615-633
Infectious arthritis is characterized radiographically by soft-tissue swelling, subchondral
bone destruction and sclerosis, and periarticular periosteal proliferation (see Figs.
4-73 and 4-76). The radiographic changes are minimal early in the disease, usually limited
to soft-tissue swelling. By the time bony changes become evident there will be considerable
cartilage destruction. The soft-tissue swelling with infectious arthritis is usually more
extensive than that seen with other joint diseases. Poorly defined or faintly mineralized
bony proliferation may be observed at the points of ligamentous or joint capsule attachment.
Subchondral bone destruction and sclerosis will occur later in the disease and indicates
extensive destruction of articular cartilage (Fig. 4-135). Although the radiographic
changes observed with infectious arthritis are similar to those of secondary degenerative
joint disease or some immune joint diseases, the radiographic changes generally are more
severe and extensive in infectious arthritis when compared with other arthritides.