Abstract
In December 2000, the Inter-Op acetabular component (Sulzer Orthopedics Inc., TX) was recalled. Contamination by an oil-based residue that was inadvertently left in the porous coating following a change in manufacturing processes was suspected to have resulted in lack of fixation. The aim of this study was to characterize the histopathology of the these failures for consistency with this hypothesis.
Materials and methods: Four hundred and fifty cups were submitted for gross and histopathological examination. H& E stained paraffin sections of tissue taken from the socket, membranes and/or capsules from the first 100 cases were reviewed histologically using a new rating scheme which accounts for the presence and extent of inflammatory cells, wear particles, and uncharacteristic tissue features. Immunohistochemical staining was performed on paraffin sections for IL1b, IL6 and TNFa (N=10) and for lymphocytes (CD3, CD4, CD20; N=8), and lipid stains were applied to selected frozen sections.
Results: Cases were revised after ave. 6 months for pain and lack of fixation. Grossly the components had minimal attached tissue, if any. Histologically, the most common finding was extensive chronic inflammation (mostly lymphocytic), although many also had abundant acute inflammation (neutrophils and early granulation tissue). Lymphocytes were mostly common T and helper T cells. Eosinophils (cells associated with intense allergic reactions) were rare. Other uncharacteristic findings included histiocyte-rich granulomas, peculiar metal-like dust associated with silicate-like structures, vacuolated cells and unusual tissue spaces (20 – 50 mm in diameter) some of which were positive with lipid stains. Tissues stained strongly positive for IL-1b and IL-6 but only weakly for TNFa. A similar inflammatory response was noted to have spread into the capsular tissues.
Conclusion: Given the absence of conclusive bacterial cultures in the majority of cases, the histopathology seems consistent with an oil-based contaminant mixed with debris generated from the machines used at the manufacturing plant.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
