CHARACTERIZATION OF TISSUES FROM METAL-METAL THRS

Abstract

A recent study of tissues from 14 modern metal-on-metal (MM) total hips reported an intense diffuse and perivascular (p.v.) lymphocytic infiltrate, suggestive of hypersensitivity (Willert et al. Osteologie 2000; 9:2–16). This study evaluated the histopathology of tissues from modern MMs using cases obtained at revision or autopsy.

Materials and methods: 35 MM THRs or surface replacements (SRs) that failed due to dislocation, aseptic loosening, and pain or obtained at autopsy (n = 4) were used. H& E stained sections were rated semiquantitatively. Selected cases were studied by immunohistochemistry for macrophage (CD68) and lymphocyte markers (CD3, 4, 20). Wear was measured with a coordinate measuring machine.

Results: Generally, the THRs without metallosis showed minimal visible wear particles, consistent with their low measured wear (av. total wear depth was 8.25 ± 6.7 um at av. 30 mos). Although SRs had an av. linear wear depth of 46 ± 48 microns at av. 23 mos, the metal rating was also low (av. 0.8), except in 1 case with HA 3rd body induced high wear and subsequent osteolysis. Lymphocytic aggregates were not a common feature but B type cells were extensive in 1 case (THR revised for pain after 36 months) moderate in 1 autopsy SR (with CoCr metallosis due to run-in wear of an out of round component) and minimal in 4 of the SRs.

Discussion and conclusions: Extensive diffuse or p.v. lymphocytes were not a consistent finding in these 35 cases. These features were not seen in well-functioning autopsy retrieved cases with low wear rates, nor in the SR with osteolysis and the highest amount of component wear. Until the long-term local and systemic effects of metal wear products, including hypersensitivity are better understood, continued histopathological assessment of periprosthetic tissues from MM total hips is recommended.