[Case report of extensive metallosis in extra-articular tissues after unicompartmental knee joint replacement]

The authors present a case of extensive metallosis of the knee joint resulting from the secondary abrasive wear of components of a unicompartmental alloplasty. Eight years after medial condyle replacement, an eighty-year-old patient presented with a break of the femoral component. This resulted in a rapid wear of tibial polyethylene and the development of secondary friction between two metal surfaces. The generation of a large number of metal particles produced an increase in the actual metal surface. This extensive articular metallosis affected not only intra-articular but also extraarticular tissues and the subchondral bone. Histological examination confirmed the presence of a large amount of opaque pigment in histiocytes. The condition was treated by total knee arthroplasty with resection of the posterior cruciate ligament (stabilizing plateau). The authors discuss the causes of metallosis development and its various types; they draw attention to the scarcity of literature data on this condition. Metallosis is a combined chemical and toxic reaction which, if the contact surface of a metal implant is large, may cause extensive damage to the surrounding tissue, the bone included.