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

Abstract

Purpose: To ascertain whether molecularsubcategories of disease progression exist withinestablished histological grades of articular cartilage(AC). Methods: Based on H&E and safranin-O stainingof AC sections obtained from 18 knee arthroplastysurgeries, 30 samples ranging from Mankin ScoringSystem grade 1 through 5 were identified. Immuno-histochemical (IHC) analysis for collagen type II andaggrecan was performed on serial sections of theparaffin-embedded AC samples. Six AC samples fromeach of the five Mankin Scoring System grades wereexamined. Results: Significant IHC differences incollagen type II and aggrecan deposition were seenwithin AC samples from all five histological grades. Therange of IHC differences in collagen type II andaggrecan increased with increasing histological grade. Achange in the pattern of collagen type II deposition wasobserved in MG-3 AC that was consistent with a switchin collagen type II metabolism. Conclusions: IHCstaining of collagen type II and aggrecan can identifydifferences within histological grades of AC that areconsistent with the existence of molecular subcategories.These differences were detectable even within the lowesthistological grades; therefore the use of IHC staining canfurther enhance and refine the scoring of ACdeterioration in early osteoarthritis (OA). Furthermore,the changes seen in the deposition pattern for bothaggrecan and collagen type II suggest that they could beused to monitor key molecular events in OAprogression. These findings also underscore the need forthe development of IHC scoring criteria.