Pleomorphic sarcoma secondary to proximal femoral epiphysiolysis with bone infarction over 4 years after cementless total hip replacement in a dog.

Objective: To report a capital physeal fracture as the result of a bone infarction with subsequent neoplastic transformation 4 years following total hip replacement.

Study design: Case report.

Animals: Five-year-old female spayed golden retriever.

Methods: The dog was initially presented for evaluation of a 2 week history of spontaneous right hind-limb lameness. Pelvic radiographs demonstrated a displaced capital epiphysis and proximal femur changes consistent with a bone infarction. A cementless total hip replacement was performed, and limb function returned to normal until 51 months after surgery. A radiolucency adjacent to the femoral stem at the greater trochanter, partial calcar resorption, and stable implants were present on pelvic radiographs acquired 52 months after surgery. Surgical exploration of the surgical site for tissue collection for histopathology and bacteria culture was performed 58 months following surgery. No bacterial growth occurred and histologic findings were nonspecific. A right hind-limb amputation was performed 61 months after total hip replacement due to the dog's progression to a non-weight-bearing lameness, Additional tissue samples were taken from the femur for histopathologic examination.

Results: Histopathologic examination was consistent with a pleomorphic sarcoma. No metallic or polyethylene particulate debris was present. Nine months after surgery there was evidence of regional and distant spread of the neoplasia.

Conclusion: In similar cases, submitting the femoral head for histopathologic examination should be considered at the time of the hip replacement surgery. If bone infarction is diagnosed as a causative agent, given the possibility of malignant transformation, long-term serial radiographic monitoring should be given serious consideration.