Presence of pannus-like tissue on osteoarthritic cartilage and its histological character

Abstract

Objective: To investigate and characterize pannus-like tissue which is often present on osteoarthritic articular cartilage.

Design: 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.

Results: 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.

Conclusion: 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.