Elusive Differential of a Painful Unstable Total Knee Arthroplasty - Metal on Cement Disease.

Particle disease from the release of metal, cement, ceramic, or polyethylene particles is a rare condition in total knee replacement. Wear, fracture, or corrosion of the components leads to foreign body reaction in the joint, followed by pain, swelling, limited motion, difficulty in walking, functional disability, and occasional systemic disease. This paper presents two cases of metal-on-cement disease as an etiology for the implant failure wherein the metal particles were shed off from the implant, along with cement and polyethylene particles, leading to a complex foreign body reaction in the failed total knee. We have coined this phenomenon as "cementallosis." Initial symptoms and signs from implant failure in both patients were mild, intermittent mediolateral knee pain that was aggravated after walking but no pain at rest or at night. The pain was associated with a 'buckling' sensation, recurrent knee swelling, and gradually worsening knee range of motion. Clinical examination in both cases was suggestive of a well-healed anterior midline surgical scar, mild to moderate effusion, mild diffuse tenderness over the entire joint, limited functional range of motion, grade 1+ laxity throughout the range of motion, and intact distal neurovascular status. Routine blood and synovial fluid workup were inconclusive for identifying the exact etiology of the patient's symptoms. Radiographs, computed tomography (CT) scans, as well as bone scans, were negative for prosthetic joint infection, component malalignment, polyethylene wear, maltracking, or loosening of the components but showed mild to moderate effusions, synovial hypertrophy, and mild scattered periprosthetic osteolysis. Intraoperatively, there was significant synovial hypertrophy with dark pigment deposition and apparent dissociation of the femoral and tibial components from the underlying cement mantle, although the cement was well-adhered to the underlying bone. Synovial fluid and multiple tissue specimens were suggestive of complex foreign body granulomas with metal, cement, and polyethylene particles. These patients had undergone surgery by the same surgery team in the community using the same implant. These cases demonstrate the failure of a total knee arthroplasty implant at the metal-cement interface with features of adverse local tissue reactions that resemble a pseudotumor from the metal-on-metal disease in the knee joint. We have compared and contrasted the clinical presentations, laboratory, imaging, histopathological, and intraoperative study findings in these cases. Knowing what to look for will aid in early diagnosis, ordering necessary investigations, better surgery planning, reducing operative time, as well as improving outcomes and cost of care. The aim of this paper is to educate the audience about this new phenomenon as a cause of knee prosthesis failure produced by a complex pseudotumor-like foreign body reaction that involves metal, cement, and polyethylene particles.