Review Question - QID 5803

Figure A demonstrates the typical perivascular and diffuse infiltrates of T- and B-lymphocytes characteristic of metal-on-metal-related delayed type hypersensitivity (DTH).

The EFFECTOR cell of DTH is the T-CELL. The MOST COMMON cell is the MACROPHAGE, as most DTH-participating cells are macrophages and only 5% of cells present are lymphocytes. Histological examination of the pseudocapsule will reveal BOTH T- and B-lymphocytes. Besides perivascular and diffuse lymphocytic infiltrates, there are also secondary lymphoid follicles suggestive of a hypersensitivity reaction. Released soluble metal (from metal degradation) can activate the immune system by forming complexes with native proteins, creating antigens/allergens. Polymeric wear debris is not known to be a major source of allergic-type immune response.

Jacobs et al. reviewed MOM bearing surfaces. They state that the incidence of metal hypersensitivity (type IV delayed-type hypersensitivity) is 25% in patients with well and poorly functioning implants (twice the general population) and 50-60% in patients with failed implants awaiting revision. The authors note that metal sensitizers include nickel (most common), followed by cobalt and chromium. Metal antigen–sensitized T-cell DTH (T-DTH) lymphocytes release cytokines that recruit and activate macrophages, monocytes, neutrophils, and other inflammatory cells. Activated macrophages activate more T cells, which in turn activates more macrophages, which activates more T cells, and so on.

Figures:
Figure A shows perivascular and diffuse lymphocytic infiltrates in the joint pseudocapsule from a MOM total hip.

Incorrect Answers:
Answer 1: There is a paucity of particle-laden histiocytes (compared with conventional metal-on-polyethylene articulations) because of low wear rates and lesser wear particle volume.
Answers 2 and 3: Both T- and B-lymphocytes are seen.
Answer 5: Particle-laden macrophages are typical of metal-on-polyethylene bearing surfaces.