PRESENTATION: 8 year old FS Greyhound presented with left hind limb lameness associated with a probable tumor in the left distal tibia.
HISTORY: The radiographic appearance of the lesion was consistent with a bony tumor and fungal serology was negative. A bone scan revealed a possible metastatic lesion in the right hind limb, therefore amputation of the left hind limb was not ideal.
PHYSICAL EXAMINATION: No abnormalities were noted apart from the left hind limb lameness.
DIAGNOSIS: Possible metastatic appendicular osteosarcoma. Preoperative blood work was essentially normal. Thoracic radiographs were not indicative of pulmonary metastasis.
TREATMENT: Limb-sparing surgery was performed to remove the affected distal tibia en bloc and place a cortical bone allograft stabilized with a bone plate. Samarium therapy was performed 1 month postoperatively due to the possible metastatic bone lesion in the right distal tibia.
OUTCOME: Marked bone marrow suppression developed post-Samarium treatment therefore systemic chemotherapy with cisplatin was postponed until it resolved. Bony resorption of 50% of the cortical graft was evident on 10 week postoperative films. This did not resolve by 5 months postoperatively, therefore a cancellous bone graft was placed at the tibial non-union site. Pulmonary metastasis and hypertrophic pulmonary osteopathy developed 1 year postoperatively. The patient's life span from the time of surgery was 15 months.
DISCUSSION: The ideal candidates for limb-sparing surgery are patients with OSA of the distal radius that affects less than 50% of the bone.
Samarium is an intravenous radioisotope with selective bony uptake. Its primary side effect is pancytopenia. The bone marrow suppression in this case deleteriously affected healing of the bone allograft, and treatment should be delayed until graft healing is complete.
Amputation and cisplatin chemotherapy provides survival of 50% to 1 year, 25% to 2 years and 10% to 3 years. Amputation was not performed in this patient since there was a possible metastatic lesion in the contralateral hindlimb that would have rendered her non-ambulatory if it progressed and became painful.
