Review Question - QID 631

In metal-on-metal articulations, it is thought that particulate wear debris stimulates lymphocytic invasion due to nanometer sized wear particles combining with native proteins to form haptens. These haptens then stimulate an immune response similar to a delayed type 4 hypersensitivity reaction via stimulation and activation of T-cells (lymphocytes).

Metal-on-metal prostheses generate less volumetric wear than metal-on-poly prostheses, and produce smaller, nanometer-sized wear particles. Two types of adverse reactions have been noted in failed metal-on-metal articulations: 1) perivascular infiltrate of lymphocytes indicative of a delayed-type hypersensitivity response to metal wear products and 2) an aseptic, lymphocyte-dominated, vasculitis-associated lesion (ALVAL). The histopathology of pseudotumors or adverse local tissue reactions has been shown to be consistent with ALVAL.

Heisel et al. reviews the alternative bearing choices for total hip arthroplasty. Ceramic and metal-on-metal bearings have demonstrated reduced wear rates compared to metal-on-poly articulations. However, long term clinical results have yet to determine any clinical improvement.

Davies et al. evaluated periprosthetic tissue samples from 25 metal-on-metal total hip replacements and compared them to samples from metal-on-poly total hips and osteoarthritic hips. A unique lymphocytic infiltrate was demonstrated in the metal-on-metal hips. The body's immune response to metallic debris is different than its response to osteoarthritis and polyethylene debris.

Plummer et. al demonstrates that ALVAL lesion severity doesn't necessarily correlate with metal ion levels (what we would assume would be higher wear). There does seem to be a predominance of monocytes in the synovial fluid however in those with ALVAL lesions -- again maybe the downstream effectors of the lymphocytic activation if the type 4 reaction is true.

Illustration A demonstrates the annual linear wear rate of different material combinations used in total hip arthropalsty.

Incorrect Answers:
Answer 1: Neutrophils are typically stimulated as part of the response to infection not particulate wear debris.
Answer 2 & 3: Macrophage, fibroblasts and giant cells are released in response to the particulate wear debris created from metal-on-polyethylene articulations not metal-on-metal articulations. They may be subsequently recruited by lymphocytes in delayed hypersensitivity reactions but they are not believed to be the initial activators of the response like lymphocytes are.
Answer 4: Eosinophilic granuloma formation results from the clonal proliferation of Langerhans-type histiocytes and is not related to wear debris.