Histological scoring of articular cartilage alone provides an incomplete picture of osteoarthritic disease progression

Purpose: To ascertain whether molecular subcategories of disease progression exist within established histological grades of articular cartilage (AC). Methods: Based on H&E and safranin-O staining of AC sections obtained from 18 knee arthroplasty surgeries, 30 samples ranging from Mankin Scoring System grade 1 through 5 were identified. Immunohistochemical (IHC) analysis for collagen type II and aggrecan was performed on serial sections of the paraffin-embedded AC samples. Six AC samples from each of the five Mankin Scoring System grades were examined. Results: Significant IHC differences in collagen type II and aggrecan deposition were seen within AC samples from all five histological grades. The range of IHC differences in collagen type II and aggrecan increased with increasing histological grade. A change in the pattern of collagen type II deposition was observed in MG-3 AC that was consistent with a switch in collagen type II metabolism. Conclusions: IHC staining of collagen type II and aggrecan can identify differences within histological grades of AC that are consistent with the existence of molecular subcategories. These differences were detectable even within the lowest histological grades; therefore the use of IHC staining can further enhance and refine the scoring of AC deterioration in early osteoarthritis (OA). Furthermore, the changes seen in the deposition pattern for both aggrecan and collagen type II suggest that they could be used to monitor key molecular events in OA progression. These findings also underscore the need for the development of IHC scoring criteria.