Morphological and biomechanical studies of rheumatoid pannus and cartilage.

Invasive pannus or granulation tissue was observed in 0.2 mm thick slices of cartilage and adjacent subchondral bone taken from fresh metatarsal and metacarpal heads removed surgically from patients with rheumatoid arthritis. Application of stress to the slices showed "tracking" of pannus or invasive tissue between lacunae and through breaches in the subchondral plate. Softened regions in the cartilage matrix became creased and were easily distinguished from regions of normal consistency. The pannus-matrix interface was not disrupted by stresses as high as 30 g/mm2.