Review Question - QID 213938

Metal on metal (MoM) articulations have the potential to produce significant soft tissue reactions known as pseudotumors, which are lymphocyte predominated.

MoM articulations gained short-lived popularity due to their decrease rate of volumetric wear and increased stability compared to traditional metal on polyethylene components secondary to larger head size. However, as clinical experience grew, we learned that MoM hips had a failure rate that was 2-3x higher. The MoM articulation also produces much smaller wear particles than the traditional metal on polyethylene designs. These small wear particles stimulate lymphocyte recruitment, which is the main reason for pseudotumor formation. Metal ion levels (cobalt and chromium) should be evaluated in patients with these articulations.

Sukur et al review particle disease and the biological mechanisms in periprosthetic osteolysis. They report that the biologic activity produced is highly dependent on the characteristic and quantity of wear particles. They conclude that a comprehensive understanding of the biologic mechanism of failure is crucial to develop new therapeutic interventions to reverse or suppress this process.

Hasegawa et al review the immune responses to metal debris following MoM THA to determine its etiology. They report that T-cells dominate the reaction produced by MoM articulations, confirming it to be a type IV hypersensitivity reaction. They conclude that metal sensitivity is not involved in the failure of MoM THA.

Incorrect Answers:
Answer 1: Macrophages are responsible for any reaction resulting from polyethylene debris.
Answer 2 and 4 Ceramic bearings have the lowest wear rates of any bearing surface and are not drive by lymphocyte response.
Answer 5: Polyethylene on polyethylene bearings are not used in total hip arthroplasty, however, if polyethylene debris was produced it would be a macrophage drive response.