To investigate and characterize pannus-like tissue which is often present on osteoarthritic articular cartilage.
Cartilage specimens from 15 knee and five hip joints of patients with osteoarthritis (OA) undergoing arthroplasty were stained for HE and Safranin-O. They were also immunostained by antitype I collagen, type II collagen, CD68, IL-1beta and MMP3 antibodies.
Ninety percent of joints have pannus-like tissue on the articular surface, preferentially in a marginal area. The articular cartilage was divided into three regions according to the location: the marginal zone, the intermediate zone and the paraeburnated zone. Pannuslike tissue in OA knee joint occurred 45.9%, 27.5% and 11.1% of the surface of each region respectively. Histologically, pannus-like tissue could be classified into the vascular type and the fibrous type. Extracellular matrix of both types of tissues were negative for Safranin-O and type II collagen, but positive for type I collagen. IL-1beta and MMP3 expressing cells are predominant in pannus-like tissue, whereas CD68 positive cells were infiltrated in only a few samples. Vascular type tissue kept continuity with bone marrow suggesting mesenchymal origin.
Pannus-like tissue exists in advanced OA cartilage, preferentially in the marginal zone. It expressed IL-1beta and MMP3, which strongly suggests that it contributes to cartilage degradation.