Extramedullary Relapse of Multiple Myeloma After Total Knee Arthroplasty: Implications for Orthopaedic Surgeons-A Case Report and Literature Review.

Multiple myeloma (MM) is a hematologic B-cell malignancy characterized by clonal plasma cell proliferation in the bone marrow. Extramedullary disease is a more aggressive form of MM, in which monoclonal cells proliferate outside the bone marrow, forming plasmacytomas. This case highlights a 56-year-old male presenting with an extramedullary recurrence of MM in the soft tissue surrounding the incision site of his total knee arthroplasty. Fortunately, following radiation and chemotherapy, his most recent evaluation demonstrated complete resolution of the nodules within the radiation field. As orthopaedic surgeons, this case serves as an important reminder to remain vigilant about prior malignancies that may complicate perioperative management.