RT Journal Article SR Electronic T1 Bidirectional erosion of cartilage in the rheumatoid knee joint. JF Annals of the Rheumatic Diseases JO Ann Rheum Dis FD BMJ Publishing Group Ltd and European League Against Rheumatism SP 676 OP 681 DO 10.1136/ard.44.10.676 VO 44 IS 10 A1 M Bromley A1 H Bertfield A1 J M Evanson A1 D E Woolley YR 1985 UL http://ard.bmj.com/content/44/10/676.abstract AB Specimens of cartilage with contiguous bone and overlying synovial pannus were obtained from 22 rheumatoid knee joints and examined histologically using specific histochemical staining techniques. All showed significant erosions of cartilage by synovial cells, but seven specimens also showed substantial cartilage erosion by cells from the subchondral bone region. This bidirectional attack on rheumatoid knee cartilage did not represent an 'underpinning' of cartilage by synovial pannus, as judged by serial sectioning and the identification of specific cells. Whereas cartilage-pannus junctions had mainly macrophagic or fibroblastic cells, cartilage-bone lesions were usually characterised by chondroclasts and blood vessels. Lymphocytes were generally absent from all sites of cartilage erosion. The bidirectional attack on articular knee cartilage suggests that changes have occurred within the cartilage that make it vulnerable to cellular invasion and erosion. Such changes might reflect a deficiency in 'anti-invasion factors', or the exposure of hidden epitopes and subsequent immunogenicity, or a combination of both.