• Pat Campbell, Edward Ebramzadeh, Scott Nelson, Karren Takamura, Koen De Smet, and Harlan C Amstutz.
• J Vernon Luck Sr MD Orthopaedic Research Center, Orthopaedic Hospital/UCLA, 2400 S Flower Street, Los Angeles, CA 90007, USA. campbell@laoh.ucla.edu
• Clin. Orthop. Relat. Res. 2010 Sep 1; 468 (9): 2321-7.

BackgroundPseudotumor-like periprosthetic tissue reactions around metal-on-metal (M-M) hip replacements can cause pain and lead to revision surgery. The cause of these reactions is not well understood but could be due to excessive wear, or metal hypersensitivity or an as-yet unknown cause. The tissue features may help distinguish reactions to high wear from those with suspected metal hypersensitivity.Questions/PurposesWe therefore examined the synovial lining integrity, inflammatory cell infiltrates, tissue organization, necrosis and metal wear particles of pseudotumor-like tissues from M-M hips revised for suspected high wear related and suspected metal hypersensitivity causes.MethodsTissue samples from 32 revised hip replacements with pseudotumor-like reactions were studied. A 10-point histological score was used to rank the degree of aseptic lymphocytic vasculitis-associated lesions (ALVAL) by examination of synovial lining integrity, inflammatory cell infiltrates, and tissue organization. Lymphocytes, macrophages, plasma cells, giant cells, necrosis and metal wear particles were semiquantitatively rated. Implant wear was measured with a coordinate measuring machine. The cases were divided into those suspected of having high wear and those suspected of having metal hypersensitivity based on clinical, radiographic and retrieval findings. The Mann-Whitney test was used to compare the histological features in these two groups.ResultsThe tissues from patients revised for suspected high wear had a lower ALVAL score, fewer lymphocytes, but more macrophages and metal particles than those tissues from hips revised for pain and suspected metal hypersensitivity. The highest ALVAL scores occurred in patients who were revised for pain and suspected metal hypersensitivity. Component wear was lower in that group.ConclusionsPseudotumor-like reactions can be caused by high wear, but may also occur around implants with low wear, likely because of a metal hypersensitivity reaction. Histologic features including synovial integrity, inflammatory cell infiltrates, tissue organization, and metal particles may help differentiate these causes.Clinical RelevancePainful hips with periprosthetic masses may be caused by high wear, but if this can be ruled out, metal hypersensitivity should be considered.

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