Figure 2.

Knee cartilage showing increased hypertrophy and mineralization. Knee cartilage with higher Mankin scores shows increased hypertrophy (increase in collagen X staining; fast blue) and mineralization (arrowheads). Histologic assessment of the knee was performed on cartilage plugs from the medial femoral condyle, and a modified Mankin scoring system was used to assess the severity of changes in osteoarthritis (OA) articular cartilage. The Mankin grades (range 0 to 14 points) for mild (1), moderate (2), and severe (3) OA were 2 to 5, 6 to 9, and 10 to 14 points, respectively. To assess hypertrophic differentiation, collagen X staining was performed on paraffin sections after hyaluronidase (Sigma, Taufkirchen, Germany) digestion with collagen X antibody (ab58632; Abcam, Cambridge, UK) using the Vectastain ABC Elite Kit (Vector Laboratories, Peterborough, UK) and fast blue as a chromogen. To assess mineralization, the articular cartilage was analyzed using digital contact radiography (DCR), performed using a digital mammography imaging technique (Hologic, Waltham, MA, USA) operating at 25 kV in manual mode, usually at 3.8 mA, and with a film focus distance of 8 cm. See [54]. Photographs kindly provided by Martin Fuerst, University Medical Center Hamburg-Eppendorf.