Histological features of pseudotumor-like tissues from metal-on-metal hips

Abstract

Background: Pseudotumor-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/purposes: We 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.

Methods: Tissue 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.

Results: The 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.

Conclusions: Pseudotumor-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 relevance: Painful hips with periprosthetic masses may be caused by high wear, but if this can be ruled out, metal hypersensitivity should be considered.

Fig. 1

An enlarged fluid-filled bursa excised from the hip of a male patient during revision surgery for acetabular malpositioning 13 months after metal-on-metal hip resurfacing arthroplasty is shown. There is light gray discoloration and the wear measurement of the explanted component showed an annual femoral wear rate of 12.8 μm.

Fig. 2

Light micrograph showing typical histologic features of high wear cases, including organized fibrin (F), a diffuse, extensive infiltration of slate blue/gray macrophages, and a small aggregate of lymphocytes (arrows) (Stain, hematoxylin and eosin, original magnification ×40). This received an ALVAL score of 5 (2 for synovial lining, 2 for inflammatory infiltrate, and 1 for tissue organization).

Fig. 3

Light micrograph showing typical histologic features of cases revised for suspected metal sensitivity, including a thick, mostly acellular tidemark area lined by fibrin (F) and thick, dense aggregates of lymphocytes at the rear of the tissue (arrows) (Stain, hematoxylin and eosin, original magnification ×40). This received an ALVAL score of 10 (3 for synovial lining, 4 for inflammatory infiltrate, and 3 for tissue organization).

Fig. 4

Light micrograph showing dense lymphocyte aggregates behind a thick necrotic fibrous tissue layer. The tissues were from a male patient with a THA that was revised for pain after 2 years. Extensive necrosis was found at revision, but the component wear was within normal range (Stain, hematoxylin and eosin, original magnification ×40).