History
A 10-year-old 34-kg (75-lb) castrated male Australian Shepherd–type dog was evaluated for non–weight-bear-ing lameness on the left forelimb following rough play with another dog. There was no history of lameness on the limb and no history of prior medical problems. On physical examination, soft tissue swelling was detected over the proximal portions of the radius and ulna, and palpation of the area elicited signs of pain. Radiographic views of the left elbow joint were obtained (Figure 1).
Lateral (A) and craniocaudal (B) radiographic views of the left elbow joint of a 10-year-old dog with acute non–weight-bearing lameness of the left forelimb.
Citation: Journal of the American Veterinary Medical Association 231, 10; 10.2460/javma.231.10.1497
Lateral (A) and craniocaudal (B) radiographic views of the left elbow joint of a 10-year-old dog with acute non–weight-bearing lameness of the left forelimb.
Citation: Journal of the American Veterinary Medical Association 231, 10; 10.2460/javma.231.10.1497
Lateral (A) and craniocaudal (B) radiographic views of the left elbow joint of a 10-year-old dog with acute non–weight-bearing lameness of the left forelimb.
Citation: Journal of the American Veterinary Medical Association 231, 10; 10.2460/javma.231.10.1497
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
An oblique fracture of the proximal portion of the ulna extends from the medial coronoid process through the caudolateral portion of the cortex. There is an ill-defined area of osteolysis with adjacent sclerosis surrounding the fracture site (Figure 2). The osteolytic process is eccentrically located, involving the medullary cavity and caudal portion of the cortex of the ulna. The lesion does not extend into the radius or cross the joint surface. The fracture margins lack sharp demarcation and have rounded, blunt edges. No proliferative new bone production is evident in this area. A pathologic fracture was suspected. Differential diagnoses for a pathologic fracture with an area of osteolysis in the proximal portion of the ulna include primary bone tumor (eg, osteosarcoma), metastatic neoplasia (eg, carcinoma), lymphoma, fungal or bacterial osteomyelitis, or bone cyst.
Same lateral and craniocaudal radiographic views as in Figure 1. Notice the oblong osteolytic area (black arrows) that is perpendicular to the fracture sitein the proximal portion of the ulna. The lytic region is attributed to cortical boneloss from osteosarcoma.
Citation: Journal of the American Veterinary Medical Association 231, 10; 10.2460/javma.231.10.1497
Same lateral and craniocaudal radiographic views as in Figure 1. Notice the oblong osteolytic area (black arrows) that is perpendicular to the fracture sitein the proximal portion of the ulna. The lytic region is attributed to cortical boneloss from osteosarcoma.
Citation: Journal of the American Veterinary Medical Association 231, 10; 10.2460/javma.231.10.1497
Same lateral and craniocaudal radiographic views as in Figure 1. Notice the oblong osteolytic area (black arrows) that is perpendicular to the fracture sitein the proximal portion of the ulna. The lytic region is attributed to cortical boneloss from osteosarcoma.
Citation: Journal of the American Veterinary Medical Association 231, 10; 10.2460/javma.231.10.1497
Comments
Thoracic radiography did not reveal evidence of pulmonary metastasis. The fracture site was surgically explored to confirm the diagnosis of pathologic fracture and rule out any possibility of anatomic reconstruction. Cortical bone loss and soft tissue proliferation within the fracture site made anatomic reconstruction impossible. After consultation with the owners, the forelimb was amputated at the shoulder joint because a primary bone tumor such as osteosarcoma became the primary differential diagnosis. Histologic examination of the lesion confirmed the diagnosis of osteosarcoma. On follow-up examination 4.5 months after surgery, the owner reported that the dog had no appreciable problems, although repeated thoracic radiography was not performed.
Osteosarcoma is the most common primary bone neoplasm in dogs. The tumor usually originates in the metaphyses, with the most common sites being the proximal portion of the humerus, the distal portions of the radius and femur, and the proximal and distal portions of the tibia.1 It is difficult to determine the extent of infiltration by osteosarcoma on the basis of radiographic margins because it takes > 50% loss of mineralization before bone lysis is apparent radiographically.2 Imaging modalities such as magnetic resonance imaging or computed tomography may provide a more accurate assessment of the infiltrative extent of bone tumors; however, access and financial restraints make this difficult for most owners. Typically, dogs will have a history of lameness and soft tissue swelling caused by microfracutres in the weakened bone prior to a pathologic fracture occurring; however, no prior lameness was evident in the dog of this report. Appendicular osteosarcoma has a metastatic rate of 98%, with the lungs being the most common site of metastasis.3 At the time of examination, < 5% of affected dogs have radiographically detectable thoracic metastases; however, 90% die or are euthanatized within 1 year of diagnosis because of complications associated with pulmonary metastasis when amputation is the only treatment.4 A recent study5 evaluating 228 dogs with appendicular osteosarcoma found that only 4% had metastasis to regional lymph nodes at the time of limb amputation. If present, lymph node metastasis is a negative prognostic indicator for both disease-free interval and survival time.5 Amputation for palliation of pain is the most commonly performed treatment; however, adjunctive chemotherapy, radiation, or limb-sparing techniques should be considered.
- 1.↑
Thrall DE. Bone tumors versus bone infections. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 4th ed. Philadelphia: WB Saunders Co, 2002;179–182.
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Moore AS, Ogilvie GK. Tumors of bone. Managing the canine cancer patient. Yardley, Pa: Veterinary Learning Systems, 2006;565–589.
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Spodnick GJ, Berg J & Rand WM, et al. Prognosis for dogs with appendicular osteosarcoma treated by amputation alone: 162 cases (1978–1988). J Am Vet Med Assoc 1992;200:995–999.
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Dernell WS, Straw RC, Withrow SJ. Tumors of the skeletal system. In: Withrow SJ, MacEven EG, eds. Small animal clinical oncology. 3rd ed. Philadelphia: WB Saunders Co, 2001;378–380.
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Hillers KR, Dernell WS & Lafferty MG, et al. Incidence and prognostic importance of lymph node metastases in dogs with appendicular osteosarcoma: 228 cases (1986–2003). J Am Vet Med Assoc 2005;226:1364–1367.
