Periprosthetic thyroid metastasis after total knee arthroplasty: a report of two cases and review of the literature.

Total knee arthroplasty (TKA) is an attractive option for relief of pain secondary to degenerative joint disease. Overall, knee replacement surgery typically results in excellent outcomes. Nevertheless, failure caused by malalignment, infection, wear, and osteolysis is known to occur. Pain after TKA may be secondary to numerous etiologic factors-most commonly, loosening, fracture, infection, and malposition of components. This case report presents two patients who developed pain after TKA that was caused by periprosthetic thyroid metastasis and who subsequently sustained a fracture below the tibial component. Clinical and radiographic examinations, as well as surgical follow-up, are presented to underscore the need for a focused history and physical examination in the initial evaluation of a patient with a painful TKA.