Lame flat-coated retriever A 10 year old male flat-coated retriever had a palpable mass that was located in the caudal aspect of the left pelvic limb at the level of the stifle joint. The dog failed to bear weight on the affected pelvic limb during the past weeks. Radiographs were made of the limb. Caudocranial and lateral view Radiographic changes A destructive lesion was identified in the proximal tibia cranially and in the distal femur just proximal to the trochlear groove. In addition, a small destructive lesion was present in the distal patella. The bony lesions did not have any associated periosteal new bone or a prominent reactive border of new bone tissue. An 8-10 cm in diameter soft tissue mass was seen in the soft tissues just caudal and lateral to the stifle joint. A smaller soft tissue mass was identified within the joint capsule cranially just ventral to the patella. The popliteal lymph node was identified caudally. Caudocranial and lateral view with the destructive bony lesions identified Radiographic diagnosis The identification of multiple destructive bony lesions near a joint plus periarticular soft tissue masses is typical for a synovial cell sarcoma or histiocytic sarcoma. Both the elbow and stifle joints are commonly affected. Metastatic tumor to bone from another primary tumor is also possible. The lack of any bony response around the destuctive lesions makes hematogenous osteomyelitis less likely especially in a dog of this age. The diagnosis on examination of the tissue obtained by biopsy was that of a histiocytic sarcoma.
