Our aim was to investigate the molecular features of progressive severities of cartilage damage, within the phenotype of Anteromedial Gonarthrosis (AMG).

Ten medial tibial plateau specimens were collected from patients undergoing unicompartmental knee replacements. The cartilage within the area of macroscopic damage was divided into equal thirds: T1(most damaged), to T3 (least damaged). The area of macroscopically undamaged cartilage was taken as a 4th sample, N. The specimens were prepared for histological (Safranin-O and H& E staining) and immunohistochemical analysis (Type I and II Collagen, proliferation and apoptosis). Immunoassays were undertaken for Collagens I and II and GAG content. Real time PCR compared gene expression between areas T and N.

There was a decrease in OARSI grade across the four areas, with progressively less fibrillation between areas T1, T2 and T3. Area N had an OARSI grade of 0 (normal). The GAG immunoassay showed decreased levels with increasing severity of cartilage damage (p< 0.0001). There was no significant difference in the Collagen II content or gene expression between areas. The Collagen I immunohistochemistry showed increased staining within chondrocyte pericellular areas in the undamaged region (N) and immunoassays showed that the Collagen I content of this macroscopically and histologically normal cartilage, was significantly higher than the damaged areas (p< 0.0001). Furthermore, real time PCR showed a significant increase in Collagen I expression in the macroscopically normal areas compared to the damaged areas (p=0.04).

In AMG there are distinct areas, demonstrating progressive cartilage loss. We conclude that in this phenotype the Collagen I increase, in areas of macroscopically and histologically normal cartilage, may represent very early changes of the cartilage matrix within the osteoarthritic disease process. This may be able to be used as an assay of early disease and as a therapeutic target for disease modification or treatment.

The aim of this study was to investigate the molecular features of progressive severities of cartilage damage, within the phenotype of Anteromedial Osteoarthritis of the Knee (AMOA).

Ten medial tibial plateau specimens were collected from patients undergoing unicompartmental knee replacements. The cartilage within the area of macroscopic damage was divided into equal thirds: T1(most damaged), to T3 (least damaged). The area of macroscopically undamaged cartilage was taken as a 4th sample, N. The specimens were prepared for histological (Safranin-O and H& E staining) and immunohistochemical analysis (Type I and II Collagen). Immunoassays were undertaken for Collagens I and II and GAG content. Real time PCR compared gene expression between areas T and N.

There was a decrease in OARSI grade across the four areas, with progressively less fibrillation between areas T1, T2 and T3. Area N had an OARSI grade of 0 (normal).

The GAG immunoassay showed decreased levels with increasing severity of cartilage damage (ANOVA P< 0.0001). There was no significant difference in the Collagen II content or gene expression between areas. The Collagen I immunohistochemistry showed increased staining within chondrocyte territorial areas in the undamaged region (N) and immunoassays showed that the Collagen I content of this macroscopically and histologically normal cartilage, was significantly higher than the damaged areas (ANOVA P< 0.0001). Furthermore, real time PCR showed that there was a significant increase in Collagen I expression in the macroscopically normal areas (p=0.04).

In AMOA there are distinct areas, demonstrating progressive cartilage loss. We conclude that in this phenotype the Collagen I increase, in areas of macroscopically and histologically normal cartilage, may represent very early changes of the cartilage matrix within the osteoarthritic disease process. This may be able to be used as an assay of early disease and as a therapeutic target for disease modification or treatment.

Collagen type type II destruction was studied after induction of experimental OA by ACL-transection in the rat. Damage was investigated by analysis of type II collagen neoepitope expression. Cleavage of type II collagen by collagenases (MMP’s) was detected by the Col2-3/4C-short antibody and collagen denaturation by Col2-3/4m. Rats were sacrificed after 2, 7, 14, 28 and 70 days. Immunostaining was performed using the Col2-3/4C (Collagenase-cleavage site) or the Col2-3/4m antibody (denatured type II collagen).

The first changes after the ACL-transsection were chondrocyte death at the margins of the articular cartilage of both tibia and femur. At day seven a pannus-like tissue protruded from the synovial tissue over the dead cartilage. Underneath the pannus-like tissue a marked staining for the collagenase-cleavage site was observed. The dead cartilage was replaced by fibrocartilage within 4 weeks after which the staining for the collagenase cleavage neoepitope had completely disappeared.

In contrast with the peripheral cartilage, in the central part of the medial tibia and femur dead chondrocytes were found on week 2 until the last time point examined, which was not replaced by fibrocartilage in this timespan. In these areas, loss of proteoglycans, fibrillation of superficial cartilage and staining for denatured type II collagen was found. Both cartilage damage and staining for denatured collagen increased with time. Only light collagenase cleavage site staining was observed on all time points in this central location.

OA in rats after ACL-transsection can be divided in two stages. An early phase lasting about 4 weeks, in which chondrocyte remodelling of the dead cartilage follows death at the cartilage margins. In this phase marked degradation of type II collagen by collagenases occurs. The second phase, characterised by cartilage damage in the central tibia and femur, shows increased staining for denatured type II collagen but little staining for the collagenase cleavage neoepitope.