A new image analysis system was employed to quantify the main histological parameters reflecting osteoarthritic features, at the cartilage and bone levels, in the meniscectomized guinea pig model of osteoarthritis (OA).
Meniscectomized (MNX) and sham-operated (SH) guinea pigs were studied 1 and 3 months after partial meniscectomy at the medial side of the left knee (n=10 to 12 animals/group). The left proximal tibias were included in methylmethacrylate. Sections were cut and stained with safranin O or Goldner trichrome. Parameters were quantified using special programs of a Biocom image analyser. The following parameters were evaluated at the medial side of the tibia: cartilage thickness (CT); fibrillation index (FI); proteoglycan content ratio based on safranin O staining intensities (PC); chondrocyte density (CD); bone volume (BV) and subchondral bone plate thickness (SBPT). The degree of user interaction varied from manually tracing objects to almost complete computer automation.
Meniscectomy resulted in significant variations of these reproducible histomorphometric parameters both after 1 month (FI: +522%, P<0.01) and 3 months (FI: +162%, P<0.001; PC: -36.7%, P<0.001; CD: -31.8%, P<0.001; SBPT: +8.7%, P<0.05) post-operation (results expressed as percentage variation of MNX vs SH). The linear correlation analysis including data from SH and/or MNX animals at the two grouped time points revealed significant r values, in particular between cartilage (CT) and subchondral bone parameters (SBPT) (r=-0.41, P<0.01).
Contrary to scoring evaluation, this system allowed to show the time-dependent impact of the pathology with an early fibrillation of the medial tibial cartilage appearing as soon as 1 month post-surgery, and the close relationship between bone and cartilage parameters during the progression of OA.